Keysight Technologies 86120B User Manual

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Keysight 86120B Multi-Wavelength Meter

User’s Guide

Notices

ISM1-A

This document contains proprietary information that is protected by copyright. All rights are reserved.

No part of this document may reproduced in (including electronic storage and retrieval or translation into a foreign language) without prior agreement and written consent from Keysight Technologies Deutschland GmbH as governed by United States and international copywright laws.

Subject Matter

The material in this document is subject to change without notice.

Keysight Technologies makes no

warranty of any kind with regard to this printed material, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose.

Keysight Technologies shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material.

Warranty

This Keysight Technologies instrument product is warranted against defects in material and workmanship for a period of one year from date of shipment. During the warranty period, Keysight will, at its option, either repair or replace products that prove to be defective.

For warranty service or repair, this product must be returned to a service facility designated by Keysight. Buyer shall prepay shipping charges to Keysight and Keysight shall pay shipping charges to return the product to

Buyer. However, Buyer shall pay all shipping charges, duties, and taxes for products returned to Keysight from another country. Keysight warrants that its software and firmware designated by Keysight for use with an instrument will execute its programming instructions when properly installed on that instrument. Keysight does not warrant that the operation of the instrument, software, or firmware will be uninterrupted or error free.

Limitation of Warranty

The foregoing warranty shall not apply to defects resulting from improper or inadequate maintenance by Buyer, Buyer-supplied software or interfacing, unauthorized modification or misuse, operation outside of the environmental specifications for the product, or improper site preparation or maintenance.

No other warranty is expressed or implied. Keysight Technologies specifically disclaims the implied warranties of Merchantability and Fitness for a Particular Purpose.

Exclusive Remedies

The remedies provided herein are Buyer’s sole and exclusive remedies. Keysight Technologies shall not be liable for any direct, indirect, special, incidental, or consequential damages whether based on contract, tort, or any other legal theory.

Assistance

Product maintenance agreements and other customer assistance agreements are available for Keysight Technologies products. For any assistance contact your nearest Keysight Technologies Sales and Service Office.

Certification

Keysight Technologies certifies that this product met its published specifications at the time of shipment from the factory. Keysight Technologies further certifies that its calibration measurements are traceable to the

United States National Institute of Standards and Technology, NIST to the extent allowed by the Institutes’s calibration facility, and to the calibration facilities of other International Standards Organization members.

ISO 9001 Certification

Produced to ISO 9001 international quality system standard as part of our objective of continually increasing customer satisfaction through improved process control.

Safety Notices CAUTION

Caution denotes a hazard. It calls attention to a procedure which, if not correctly performed or adhered to, could result in damage to or destruction of the product. Do not proceed beyond a caution sign until the indicated conditions are fully understood and met.

WARNING

Warning denotes a hazard. It calls attention to a procedure which, if not correctly performed or adhered to, could result in injury or loss of life. Do not proceed beyond a warning sign until the indicated conditions are fully understood and met.

The instruction manual symbol. The product is marked with this warning symbol when it is necessary for the user to refer to the instructions in the manual.

The laser radiation symbol. This warning symbol is marked on products which have a laser output.

The AC symbol is used to indicate the required nature of the line module input power.

| The ON symbols are

used to mark the positions of the instrument power line switch.

m The OFF symbols

are used to mark the positions of the instrument power line switch.

The CE mark is a registered trademark of the European Community.

The CSA mark is a registered trademark of the Canadian Standards Association.

The C-Tick mark is a registered trademark of the Australian Spectrum Management Agency.

This text denotes the instrument is an Industrial Scientific and Medical Group 1 Class A product.

Typographical Conventions.

The following conventions are used in this book:

Key type for keys or text located on the keyboard or instrument.

Softkey type for key names that are displayed on the instrument’s screen.

Display type for words or characters displayed on the computer’s screen or instrument’s display.

User type for words or characters

that you type or enter.

Emphasis type for words or characters that emphasize some point or that are used as place holders for text that you type.

Edition 3: 86120-90B03: November 2014

Edition 2: 86120-90B03: July 2004 Edition 1:

The Keysight 86120B—At a Glance

The Keysight 86120B Multi-Wavelength Meter measures the wavelength and optical power of laser light in the 700-1650 nm wavelength range. Because the Keysight 86120B simultaneously measures multiple laser lines, you can characterize wavelength-division-multiplexed (WDM) systems and the multiple lines of Fabry-Perot lasers.

NOTE

The front-panel OPTICAL INPUT connector uses a single-mode input fiber.

What’s new with the Keysight 86120B

This book directly applies to Keysight 86120B instruments with firmware version number 2.0. When first turned on, the instrument briefly displays the firmware version. These instruments have the added capability of measuring broadband devices and chirped lasers. Refer to “Connect the fiber-optic cable to the front-panel OPTICAL INPUT connector.” on page 2-40.

Characterize laser lines easily

With the Keysight 86120B you can quickly and easily measure any of the following parameters:

• Wavelengths and powers

• Average wavelength

• Total optical power

• Laser line separation

• Laser drift (wavelength and power)

• Signal-to-noise ratios

• Coherence length

The Keysight 86120B—At a Glance

In addition to these measurements, a “power bar” is displayed that shows power changes like a traditional analog meter. You can see the power bar shown in the following figure of the Keysight 86120B’s display.

CAUTION The input circuitry of the Keysight 86120B can be damaged when total input

power levels exceed +18 dBm. To prevent input damage, this specified level must not be exceeded.

Print measurement results

You can get hardcopy results of your measurements by connecting a printer to the rear-panel PARALLEL PRINTER PORT connector.

Program the instrument for automatic measurements

The Keysight 86120B offers an extensive set of GPIB programming commands. These commands allow you to perform automated measurements on manufacturing production lines and remote sites. Chapter 4, “Programming” and Chapter 5, “Com-

mon Commands” provide all the information you’ll need to know in order to pro-

gram the Keysight 86120B.

Display wavelengths as if measured in vacuum or standard air

Although all measurements are made in air, displayed results are corrected for air dispersion to accurately show wavelength values in vacuum or in “standard air.” To ensure accurate wavelength measurements, make sure that you enter the elevation from which you will be making measurements as described in Chapter 1, “Getting

Started”.

The Keysight 86120B—At a Glance

Measurement accuracy—it’s up to you!

Fiber-optic connectors are easily damaged when connected to dirty or damaged cables and accessories. The Keysight

86120B’s front-panel INPUT connector is no exception. When you use improper cleaning and handling techniques, you risk expensive instrument repairs, damaged cables, and compromised measure ments.

Before you connect any fiber-optic cable to the Keysight 86120B, refer to

“Cleaning Connections for Accurate Measurements” on page 23.

General Safety Considerations

This product has been designed and tested in accordance with IEC 61010-1 and has been supplied in a safe condition. The instruction documentation contains information and warnings which must be followed by the user to ensure safe operation and to maintain the product in a safe condition.

There is no output laser aperture

The Keysight 86120B does not have an output laser aperture. However, light less than Operator maintenance or precautions are not necessary to maintain safety. No controls, adjustments, or performance of procedures result in hazardous radiation exposure.

1 nW escapes out of the front-panel OPTIC

AL INPUT connector.

General Safety Considerations

Laser Safety Information

The laser sources contained in the product specified by this user guide are classified according to IEC 60825-1 (2007).

The laser sources comply with 21 CFR 1040.10 except for deviations pursuant to Laser Notice No. 50 dated 2007-June-24.

Table 1-1. Safety Information for Wavelength Meter

86120B

Laser type HeNe Laser

Wavelength (±0.1 nm) 632.8 nm

Max. CW output power

Beam waist diameter 9 µm

Numerical aperture 0.1

< 1 nW

Laser Class according to IEC 608251 (2007)

Max. permissible CW output power 0.39 mW

Max. CW output power is defined as the highest possible optical power that

the laser source can produce at its output connector

Class 1

General Safety Considerations

WARNING If this instrument is not used as specified, the protection provided

by the equipment could be impaired. This instrument must be used in a normal condition (in which all means for protection are intact) only.

WARNING No operator serviceable parts inside. Refer servicing to qualified

personnel. To prevent electrical shock, do not remove covers.

WARNING To prevent electrical shock, disconnect the Keysight 86120B from

mains before cleaning. Use a dry cloth or one slightly dampened with water to clean the external case parts. Do not attempt to clean internally.

WARNING This is a Safety Class 1 product (provided with protective earth).

The mains plug shall only be inserted in a socket outlet provided with a protective earth contact. Any interruption of the protective conductor inside or outside of the product is likely to make the product dangerous. Intentional interruption is prohibited.

WARNING For continued protection against fire hazard, replace line fuse only

with same type and ratings, (Fuse type F 6.3 A/250V, IEC 60127 type 5x20mm). The use of other fuses or materials is prohibited.

CAUTION This product complies with Overvoltage Category II and Pollution Degree 2.

General Safety Considerations

CAUTION VENTILATION REQUIREMENTS: When installing the product in a

cabinet, the convection into and out of the product must not be restricted. The ambient temperature (outside the cabinet) must be less than the maximum operating temperature of the product by 4

⋅C for every 100 watts dissipated in

the cabinet. If the total power dissipated in the cabinet is greater than 800 watts, then forced convection must be used.

CAUTION Always use the three-prong ac power cord supplied with this instrument.

Failure to ensure adequate earth grounding by not using this cord may cause instrument damage.

CAUTION Do not connect ac power until you have verified the line voltage is correct as

described in

“Line Power Requirements” on page 1-16. Damage to the equipment

could result.

CAUTION This instrument has autoranging line voltage input. Be sure the supply

voltage is within the specified range.

General Safety Considerations

Contents

The Keysight 86120B—At a Glance 3

General Safety Considerations 6

1 Getting Started

Step 1. Inspect the Shipment 15 Step 2. Connect the Line-Power Cable 16 Step 3. Connect a Printer 17 Step 4. Turn on the Keysight 86120B 18 Step 5. Enter Your Elevation 20 Step 6. Select Medium for Wavelength Values 21 Step 7. Turn Off Wavelength Limiting 22 Cleaning Connections for Accurate Measurements 23 Returning the Instrument for Service 34

2 Using the Multi-Wavelength Meter

Displaying Wavelength and Power 39 Changing the Units and Measurement Rate 49 Defining Laser-Line Peaks 52 Measuring Laser Separation 56 Measuring Modulated Lasers 60 Measuring Total Power Greater than 10 dBm 62 Calibrating Measurements 63 Printing Measurement Results 65

3 Measurements Applications

Measuring Signal-to-Noise Ratios 69 Measuring Signal-to-Noise Ratios with Averaging 73 Measuring Laser Drift 75 Measuring Coherence Length 78

4 Programming

Addressing and Initializing the Instrument 83 Making Measurements 85 Monitoring the Instrument 96 Reviewing SCPI Syntax Rules 103 Example Programs 108 Lists of Commands 123

5 Programming Commands

Common Commands 133 Measurement Instructions 146 CALCulate1 Subsystem 157 CALCulate2 Subsystem 162 CALCulate3 Subsystem 174 CONFigure Measurement Instruction 196 DISPlay Subsystem 196 FETCh Measurement Instruction 199 HCOPy Subsystem 200 MEASure Measurement Instruction 200 READ Measurement Instruction 201 SENSe Subsystem 201 STATus Subsystem 206 SYSTem Subsystem 211 TRIGger Subsystem 216 UNIT Subsystem 218

6 Performance Tests

Test 1. Absolute Wavelength Accuracy 221 Test 2. Sensitivity 222 Test 3. Polarization Dependence 223 Test 4. Optical Input Return Loss 224 Test 5. Amplitude Accuracy and Linearity 226

7 Specifications and Regulatory Information

Definition of Terms 233 Specifications 235 General Safety Information 239 Compliance with Canadian EMC Requirements 239 Notice for Germany: 239 Declaration of Conformity 240 Product Overview 241

8 Reference

Instrument Preset Conditions 244 Menu Maps 246 Error Messages 253 Connector interfaces (order separately) 259 Power Cords 260 For Assistance and Support 262

Getting Started

The instructions in this chapter show you how to install your Keysight 86120B. You should be able to finish these procedures in about ten to twenty minutes. After you’ve completed this chapter, continue with Chapter 2, “Using the Multi-Wave-

length Meter”. Refer to Chapter 7, “Specifications and Regulatory Information” for

information on operating conditions such as temperature.

CAUTION Install the instrument so that the ON/OFF switch is readily identifiable and is

easily reached by the operator. The ON/OFF switch or the detachable power cord is the instrument disconnecting device. It disconnects the mains circuits from the mains supply before other parts of the instrument. Alternately, an externally installed switch or circuit breaker (which is really identifiable and is easily reached by the operator) may be used as a disconnecting device.

CAUTION Install the instrument according to the enclosure protection provided. This

instrument does not protect against the ingress of water. This instrument protects against finger access to hazardous parts within the enclosure.

Getting Started

Step 1. Inspect the Shipment

1 Verify that all system components ordered have arrived by comparing the shipping

forms to the original purchase order. Inspect all shipping containers.

If your shipment is damaged or incomplete, save the packing materials and notify both the shipping carrier and the nearest Keysight Technologies sales and service office. Keysight Technologies will arrange for repair or replacement of damaged or incomplete shipments without waiting for a settlement from the transportation company. Notify the Keysight Technologies customer engineer of any problems.

2 Make sure that the serial number and options listed on the instrument’s rear-panel

label match the serial number and options listed on the shipping document.

Getting Started

Step 2. Connect the Line-Power Cable

WARNING This is a Safety Class 1 Product (provided with protective earth).

The mains plug shall only be inserted in a socket outlet provided with a protective earth contact. Any interruption of the protective conductor inside or outside of the instrument is likely to make the instrument dangerous. Intentional interruption is prohibited.

CAUTION Always use the three-prong AC power cord supplied with this instrument.

Failure to ensure adequate earth grounding by not using this cord may cause instrument damage.

CAUTION Do not connect ac power until you have verified the line voltage is correct as

described in the following paragraphs. Damage to the equipment could result.

CAUTION This instrument has autoranging line voltage input. Be sure the supply

voltage is within the specified range.

1 Verify that the line power meets the requirements shown in the following table.

Line Power Requirements

Voltage max. 100 / 115 / 230 / 240 V~

Frequency 50 / 60 Hz

2 Connect the line-power cord to the instrument’s rear-panel connector.

3 Connect the other end of the line-power cord to the power receptacle.

Getting Started

Step 3. Connect a Printer

Various power cables are available to connect the Keysight 86120B to ac power outlets unique to specific geographic areas. The cable appropriate for the area to which the Keysight 86120B is originally shipped is included with the unit. The cable shipped with the instrument also has a right-angle connector so that the Keysight 86120B can be used while sitting on its rear feet. You can order additional ac power cables for use in different geographic areas. Refer to “Connector interfaces

(order separately)” on page 259.

Step 3. Connect a Printer

The Keysight 86120B can print hardcopies of measurement results on a printer. The output is ASCII text. If you don’t have a printer, continue with .

• Using a standard parallel printer cable, connect the printer to the Keysight 86120B’s rear-panel PARALLEL PRINTER PORT connector.

Getting Started

Step 4. Turn on the Keysight 86120B

CAUTION The front panel LINE switch disconnects the mains circuits from the mains

supply after the EMC filters and before other parts of the instrument.

1 Press the front-panel LINE key. After approximately 20 seconds, the display should

look similar to the following figure:

The front-panel LINE switch disconnects the mains circuits from the mains supply after the EMC filters and before other parts of the instrument.

2 If the Keysight 86120B fails to turn on properly, consider the following possibilities:

• Is the line fuse good?

• Does the line socket have power?

• Is it plugged into the proper ac power source?

If the instrument still fails, return it to Keysight Technologies for repair. Refer to

“Returning the Instrument for Service” on page 34.

Getting Started

Step 4. Turn on the Keysight 86120B

Instrument firmware version

When the instrument is first turned on, the display briefly shows the instrument’s firmware version number. In the unlikely event that you have a problem with the Keysight

86120B, you may need to indicate this number when commu-

nicating with Keysight Technologies.

There is no output laser aperture

The Keysight 86120B does not have an output laser aperture. However, light less than 1

nw escapes out of the front-panel OPTICAL INPUT connector. Operator maintenance or precautions are not necessary to maintain safety. No controls, adjustments, or performance of procedures result in hazardous radia

tion exposure.

Measurement accuracy—it’s up to you!

Fiber-optic connectors are easily damaged when connected to dirty or damaged cables and accessories. The Keysight

86120B’s front-panel INPUT connector is no exception. When you use improper cleaning and handling techniques, you risk expensive instrument repairs, damaged cables, and compromised measure ments.

Before you connect any fiber-optic cable to the Keysight 86120B, refer to

“Cleaning Connections for Accurate Measurements” on page 23.

Getting Started

3.281

-------------

Step 5. Enter Your Elevation

In order for your Keysight 86120B to accurately measure wavelengths and meet its published specifications, you must enter the elevation where you will be performing your measurements.

1 Press the Setup key.

2 Press the MORE softkey.

3 Press the CAL softkey.

4 Press ELEV.

5 Use the and softkeys to enter the elevation in meters. Entries jump in 500

meter steps from 0 m to 5000 m.

The elevation value selected with the softkeys must be within 250 meters of the actual elevation.

6 Press RETURN to complete the entry.

Converting feet to meters

If you know your elevation in feet, you can convert this value to meters by using the following equation:

Getting Started

Step 6. Select Medium for Wavelength Values

Because wavelength varies with the material that the light passes through, the Keysight 86120B offers wavelength measurements in two mediums: vacuum and standard air.

1 Press the Setup key.

2 Press the MORE softkey.

3 Press the CAL softkey.

4 Make the following selection:

• Press VACUUM for wavelength readings in a vacuum.

• Press STD AIR for wavelength readings in standard air.

5 Press RETURN to complete the entry.

Definition of standard air

Standard air is defined to have the following characteristics:

Barometric pressure: 760 torr Temperature: 15⋅C Relative humidity: 0%

Getting Started

Step 7. Turn Off Wavelength Limiting

After the Preset key is pressed, the input wavelength range is limited to measuring lasers between 1200 nm and 1650 nm. You can easily expand the input range to the full 700 nm to 1650 nm range with the following steps:

1 Press the Preset key.

2 Press the Setup key.

3 Press the WL LIM softkey.

4 Press LIM OFF to remove the limits on wavelength range.

All responses in the full 700 nm to 1650 nm range are now displayed.

Getting Started

Cleaning Connections for Accurate Measurements

Today, advances in measurement capabilities make connectors and connection techniques more important than ever. Damage to the connectors on calibration and verification devices, test ports, cables, and other devices can degrade measurement accuracy and damage instruments. Replacing a damaged connector can cost thousands of dollars, not to mention lost time! This expense can be avoided by observing the simple precautions presented in this book. This book also contains a brief list of tips for caring for electrical connectors.

Choosing the Right Connector

A critical but often overlooked factor in making a good lightwave measurement is the selection of the fiber-optic connector. The differences in connector types are mainly in the mechanical assembly that holds the ferrule in position against another identical ferrule. Connectors also vary in the polish, curve, and concentricity of the core within the cladding. Mating one style of cable to another requires an adapter. Keysight Technologies offers adapters for most instruments to allow testing with many different cables. Figure 1-1 on page 24 shows the basic components of a typical connectors.

The system tolerance for reflection and insertion loss must be known when selecting a connector from the wide variety of currently available connectors. Some items to consider when selecting a connector are:

• How much insertion loss can be allowed?

• Will the connector need to make multiple connections? Some connectors are better than others, and some are very poor for making repeated connections.

• What is the reflection tolerance? Can the system take reflection degradation?

• Is an instrument-grade connector with a precision core alignment required?

• Is repeatability tolerance for reflection and loss important? Do your specifications

Getting Started

Cleaning Connections for Accurate Measurements

take repeatability uncertainty into account?

• Will a connector degrade the return loss too much, or will a fusion splice be required? For example, many DFB lasers cannot operate with reflections from connectors. Of ten as much as 90 dB isolation is needed.

Figure 1-1. Basic components of a connector.

Over the last few years, the FC/PC style connector has emerged as the most popular connector for fiber-optic applications. While not the highest performing connector, it represents a good compromise between performance, reliability, and cost. If properly maintained and cleaned, this connector can withstand many repeated connections.

However, many instrument specifications require tighter tolerances than most connectors, including the FC/PC style, can deliver. These instruments cannot tolerate connectors with the large non-concentricities of the fiber common with ceramic style ferrules. When tighter alignment is required, Keysight Technologies instruments typically use a connector such as the Diamond HMS-10, which has concentric tolerances within a few tenths of a micron. Keysight Technologies then uses a special universal adapter, which allows other cable types to mate with this precision connector. See Figure 1-2.

Getting Started

Cleaning Connections for Accurate Measurements

Figure 1-2. Universal adapters to Diamond HMS-10.

The HMS-10 encases the fiber within a soft nickel silver (Cu/Ni/Zn) center which is surrounded by a tough tungsten carbide casing, as shown in Figure 1-3.

Figure 1-3. Cross-section of the Diamond HMS-10 connector.

The nickel silver allows an active centering process that permits the glass fiber to be moved to the desired position. This process first stakes the soft nickel silver to fix the fiber in a near-center location, then uses a post-active staking to shift the fiber into the desired position within 0.2 μm. This process, plus the keyed axis, allows very precise core-to-core alignments. This connector is found on most Keysight Technologies lightwave instruments. The soft core, while allowing precise centering, is also the chief liability of the connector. The soft material is easily damaged. Care must be taken to minimize excessive scratching and wear. While minor wear is not a problem if the glass face is not affected, scratches or grit can cause the glass fiber to move out of alignment. Also, if unkeyed connectors are used, the nickel sil-

Getting Started

Cleaning Connections for Accurate Measurements

ver can be pushed onto the glass surface. Scratches, fiber movement, or glass contamination will cause loss of signal and increased reflections, resulting in poor return loss.

Inspecting Connectors

Because fiber-optic connectors are susceptible to damage that is not immediately obvious to the naked eye, poor measurements result without the user being aware. Microscopic examination and return loss measurements are the best way to ensure good measurements. Good cleaning practices can help ensure that optimum connector performance is maintained. With glass-to-glass interfaces, any degradation of a ferrule or the end of the fiber, any stray particles, or finger oil can have a significant effect on connector performance. Where many repeat connections are required, use of a connector saver or patch cable is recommended.

Figure 1-4 shows the end of a clean fiber-optic cable. The dark circle in the center of

the micrograph is the fiber’s 125 μm core and cladding which carries the light. The surrounding area is the soft nickel-silver ferrule. Figure 1-5 shows a dirty fiber end from neglect or perhaps improper cleaning. Material is smeared and ground into the end of the fiber causing light scattering and poor reflection. Not only is the precision polish lost, but this action can grind off the glass face and destroy the connector.

Figure 1-6 shows physical damage to the glass fiber end caused by either repeated

connections made without removing loose particles or using improper cleaning tools. When severe, the damage of one connector end can be transferred to another good connector endface that comes in contact with the damaged one. Periodic checks of fiber ends, and replacing connecting cables after many connections is a wise practice. The cure for these problems is disciplined connector care as described in the following list and in “Cleaning Connectors” on page 30.

Getting Started

Cleaning Connections for Accurate Measurements

Use the following guidelines to achieve the best possible performance when making measurements on a fiber-optic system:

• Never use metal or sharp objects to clean a connector and never scrape the connector.

• Avoid matching gel and oils.

Figure 1-4. Clean, problem-free fiber end and ferrule.

Figure 1-5. Dirty fiber end and ferrule from poor cleaning.

Getting Started

Cleaning Connections for Accurate Measurements

Figure 1-6. Damage from improper cleaning.

While these often work well on first insertion, they are great dirt magnets. The oil or gel grabs and holds grit that is then ground into the end of the fiber. Also, some early gels were designed for use with the FC, non-contacting connectors, using small glass spheres. When used with contacting connectors, these glass balls can scratch and pit the fiber. If an index matching gel or oil must be used, apply it to a freshly cleaned connector, make the measurement, and then immediately clean it off. Never use a gel for longer-term connections and never use it to improve a damaged connector. The gel can mask the extent of damage and continued use of a damaged fiber can transfer damage to the instrument.

• When inserting a fiber-optic cable into a connector, gently insert it in as straight a line as possible. Tipping and inserting at an angle can scrape material off the inside of the connector or even break the inside sleeve of connectors made with ceramic material.

• When inserting a fiber-optic connector into a connector, make sure that the fiber end does not touch the outside of the mating connector or adapter.

• Avoid over tightening connections.

Unlike common electrical connections, tighter is not better. The purpose of the connector is to bring two fiber ends together. Once they touch, tightening only causes a greater force to be applied to the delicate fibers. With connectors that have a convex fiber end, the end can be pushed off-axis resulting in misalignment and excessive return loss. Many measurements are actually improved by backing off the connector pressure. Also, if a piece of grit does happen to get by the cleaning procedure, the tighter connection is more likely to damage the glass. Tighten the connectors just until the two fibers touch.

• Keep connectors covered when not in use.

• Use fusion splices on the more permanent critical nodes. Choose the best connector possible. Replace connecting cables regularly. Frequently measure the return loss of

Getting Started

Cleaning Connections for Accurate Measurements

the connector to check for degradation, and clean every connector, every time.

All connectors should be treated like the high-quality lens of a good camera. The weak link in instrument and system reliability is often the inappropriate use and care of the connector. Because current connectors are so easy to use, there tends to be reduced vigilance in connector care and cleaning. It takes only one missed cleaning for a piece of grit to permanently damage the glass and ruin the connector.

Measuring insertion loss and return loss

Consistent measurements with your lightwave equipment are a good indication that you have good connections. Since return loss and insertion loss are key factors in determining optical connector performance they can be used to determine connector degradation. A smooth, polished fiber end should produce a good return-loss measurement. The quality of the polish establishes the difference between the “PC” (physical contact) and the “Super PC” connectors. Most connectors today are physical contact which make glass-to-glass connections, therefore it is critical that the area around the glass core be clean and free of scratches. Although the major area of a connector, excluding the glass, may show scratches and wear, if the glass has maintained its polished smoothness, the connector can still provide a good low level return loss connection.

If you test your cables and accessories for insertion loss and return loss upon receipt, and retain the measured data for comparison, you will be able to tell in the future if any degradation has occurred. Typical values are less than 0.5 dB of loss, and sometimes as little as 0.1 dB of loss with high performance connectors. Return loss is a measure of reflection: the less reflection the better (the larger the return loss, the smaller the reflection). The best physically contacting connectors have return losses better than 50 dB, although 30 to 40 dB is more common.

Getting Started

Cleaning Connections for Accurate Measurements

Visual inspection of fiber ends

Visual inspection of fiber ends can be helpful. Contamination or imperfections on the cable end face can be detected as well as cracks or chips in the fiber itself. Use a microscope (100X to 200X magnification) to inspect the entire end face for contamination, raised metal, or dents in the metal as well as any other imperfections. Inspect the fiber for cracks and chips. Visible imperfections not touching the fiber core may not affect performance (unless the imperfections keep the fibers from contacting).

WARNING Always remove both ends of fiber-optic cables from any

instrument, system, or device before visually inspecting the fiber ends. Disable all optical sources before disconnecting fiber-optic cables. Failure to do so may result in permanent injury to your eyes.

Cleaning Connectors

The procedures in this section provide the proper steps for cleaning fiber-optic cables and Keysight Technologies universal adapters. The initial cleaning, using the alcohol as a solvent, gently removes any grit and oil. If a caked-on layer of material is still present, (this can happen if the beryllium-copper sides of the ferrule retainer get scraped and deposited on the end of the fiber during insertion of the cable), a second cleaning should be performed. It is not uncommon for a cable or connector to require more than one cleaning.

CAUTION Keysight Technologies strongly recommends that index matching

compounds not be applied to their instruments and accessories. Some compounds, such as gels, may be difficult to remove and can contain

Getting Started

Cleaning Connections for Accurate Measurements

damaging particulates. If you think the use of such compounds is necessary, refer to the compound manufacturer for information on application and cleaning procedures.

Table 1-2. Cleaning Accessories

Item Keysight Technologies Part Number

Pure isopropyl alcohol —

Cotton swabs 8520-0023

Small foam swabs 9300-1223

Compressed dust remover (non-residue) 8500-5262

Table 1-3. Dust Caps Provided with Lightwave Instruments

Item Keysight Technologies Part Number

Laser shutter cap 08145-64521

FC/PC dust cap 08154-44102

Biconic dust cap 08154-44105

DIN dust cap 5040-9364

HMS10/dust cap 5040-9361

ST dust cap 5040-9366

To clean a non-lensed connector

CAUTION Do not use any type of foam swab to clean optical fiber ends. Foam swabs can

leave filmy deposits on fiber ends that can degrade performance.

1 Apply pure isopropyl alcohol to a clean lint-free cotton swab or lens paper.

Getting Started

Cleaning Connections for Accurate Measurements

Cotton swabs can be used as long as no cotton fibers remain on the fiber end after cleaning.

2 Clean the ferrules and other parts of the connector while avoiding the end of the fiber.

3 Apply isopropyl alcohol to a new clean lint-free cotton swab or lens paper.

4 Clean the fiber end with the swab or lens paper.

Do not scrub during this initial cleaning because grit can be caught in the swab and become a gouging element.

5 Immediately dry the fiber end with a clean, dry, lint-free cotton swab or lens paper.

6 Blow across the connector end face from a distance of 6 to 8 inches using filtered,

dry, compressed air. Aim the compressed air at a shallow angle to the fiber end face.

Nitrogen gas or compressed dust remover can also be used.

CAUTION Do not shake, tip, or invert compressed air canisters, because this releases

particles in the can into the air. Refer to instructions provided on the compressed air canister.

7 As soon as the connector is dry, connect or cover it for later use.

If the performance, after the initial cleaning, seems poor try cleaning the connector again. Often a second cleaning will restore proper performance. The second cleaning should be more arduous with a scrubbing action.

To clean an adapter

The fiber-optic input and output connectors on many Keysight Technologies instruments employ a universal adapter such as those shown in the following picture. These adapters allow you to connect the instrument to different types of fiber-optic cables.

Figure 1-7. Universal adapters.

1 Apply isopropyl alcohol to a clean foam swab.

Cotton swabs can be used as long as no cotton fibers remain after cleaning. The foam

Getting Started

Cleaning Connections for Accurate Measurements

swabs listed in this section’s introduction are small enough to fit into adapters.

Although foam swabs can leave filmy deposits, these deposits are very thin, and the risk of other contamination buildup on the inside of adapters greatly outweighs the risk of contamination by foam swabs.

2 Clean the adapter with the foam swab.

3 Dry the inside of the adapter with a clean, dry, foam swab.

4 Blow through the adapter using filtered, dry, compressed air.

Nitrogen gas or compressed dust remover can also be used. Do not shake, tip, or invert compressed air canisters, because this releases particles in the can into the air. Refer to instructions provided on the compressed air canister.

Getting Started

Returning the Instrument for Service

The instructions in this section show you how to properly return the instrument for repair or calibration. Always call the Keysight Technologies Instrument Support Center first to initiate service before returning your instrument to a service office. This ensures that the repair (or calibration) can be properly tracked and that your instrument will be returned to you as quickly as possible. Call this number regardless of where you are located. Refer to “For Assistance and Support” on page 262 for a list of service offices.

If the instrument is still under warranty or is covered by a Keysight Technologies maintenance contract, it will be repaired under the terms of the warranty or contract (the warranty is at the front of this manual). If the instrument is no longer under warranty or is not covered by a Keysight Technologies maintenance plan, Keysight Technologies will notify you of the cost of the repair after examining the unit.

When an instrument is returned to a Keysight Technologies service office for servicing, it must be adequately packaged and have a complete description of the failure symptoms attached. When describing the failure, please be as specific as possible about the nature of the problem. Include copies of additional failure information (such as the instrument failure settings, data related to instrument failure, and error messages) along with the instrument being returned.

Preparing the instrument for shipping

1 Write a complete description of the failure and attach it to the instrument. Include any

specific performance details related to the problem. The following information

Returning the Instrument for Service

should be returned with the instrument.

• Type of service required.

• Date instrument was returned for repair.

• Description of the problem:

• Whether problem is constant or intermittent.

• Whether instrument is temperature-sensitive.

• Whether instrument is vibration-sensitive.

• Instrument settings required to reproduce the problem.

• Performance data.

• Company name and return address.

• Name and phone number of technical contact person.

• Model number of returned instrument.

• Full serial number of returned instrument.

• List of any accessories returned with instrument.

2 Cover all front or rear-panel connectors that were originally covered when you first

received the instrument.

CAUTION Cover electrical connectors to protect sensitive components from

electrostatic damage. Cover optical connectors to protect them from damage due to physical contact or dust.

Getting Started

CAUTION Instrument damage can result from using packaging materials other than the

original materials. Never use styrene pellets as packaging material. They do not adequately cushion the instrument or prevent it from shifting in the carton. They may also cause instrument damage by generating static electricity.

3 Pack the instrument in the original shipping containers. Original materials are

available through any Keysight Technologies office. Or, use the following guidelines:

• Wrap the instrument in antistatic plastic to reduce the possibility of damage caused by electrostatic discharge.

• For instruments weighing less than 54 kg (120 lb), use a double-walled, corrugat-

Getting Started

Returning the Instrument for Service

ed cardboard carton of 159 kg (350 lb) test strength.

• The carton must be large enough to allow approximately 7 cm (3 inches) on all sides of the instrument for packing material, and strong enough to accommodate the weight of the instrument.

• Surround the equipment with approximately 7 cm (3 inches) of packing material, to protect the instrument and prevent it from moving in the carton. If packing foam is not available, the best alternative is S.D-240 Air Cap™ from Sealed Air Corpo ration (Commerce, California 90001). Air Cap looks like a plastic sheet filled with air bubbles. Use the pink (antistatic) Air Cap™ to reduce static electricity. Wrap ping the instrument several times in this material will protect the instrument and prevent it from moving in the carton.

4 Seal the carton with strong nylon adhesive tape.

5 Mark the carton “FRAGILE, HANDLE WITH CARE”.

6 Retain copies of all shipping papers.

Using the Multi-Wavelength Meter

In this chapter, you’ll learn how to make a variety of fast, accurate measurements. As you perform these measurements, keep in mind the following points:

• 700 nm to 1650 nm maximum input wavelength range

The range is normally limited from 1200 nm to 1650 nm. To use the full range, refer

to “Measuring lasers between 700 nm and 1200 nm” on page 44.

• +10 dBm maximum total displayed input power

• Laser linewidths assumed to be less than 10 GHz

• If you change the elevation where you will be using your Agilent 86120B, refer to

“Calibrating Measurements” on page 63.

• Press the green Preset key to return the Agilent 86120B to its default state.

CAUTION Do not exceed +18 dBm source power. The Agilent 86120B’s input circuitry

can be damaged when total input power exceeds 18 dBm. You can measure power levels that are greater by adding attenuation and entering a power offset as described in “To measure total power exceeding 10 dBm” on page 62.

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

This section gives you step-by-step instructions for measuring peak wavelength, average wavelength, peak power, and total input power. There are three display modes:

• Peak wavelength

• List-by-wavelength or power

• Average wavelength and total power

If the measured amplitudes are low, clean the front-panel OPTICAL INPUT connector.

This section includes:

Peak WL mode 40 List by WL or power modes 42 Total power and average wavelength 43 Measuring lasers between 700 nm and 1200 nm 44 Limiting the wavelength range 44 Measuring broadband devices and chirped lasers 46 Graphical display of optical power spectrum 47 Instrument states 48 Power bar 48

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

Peak WL mode

When Peak WL is pressed, the display shows the largest amplitude line in the spectrum. This is the peak wavelength mode. The word PEAK is shown on the screen. If multiple laser lines are present at the input, the number of lines located will be shown along the right side of the screen.

Display after “Peak WL” key pressed

In addition to the digital readouts, there is a power bar. It provides a convenient analog “meter movement” for tuning laser power.

Although the Peak WL mode shows one signal at a time, softkeys are provided that allow you to scroll through and display all the measured laser lines. You can scroll through the list according to the wavelengths or powers measured. The signals are displayed in order from shortest to longest wavelengths. The Agilent 86120B can measure up to 100 laser lines simultaneously.

To display peak wavelength and power

1 Connect the fiber-optic cable to the front-panel OPTICAL INPUT connector.

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

2 To display the peak wavelength and power, do one of the following:

• Press the green Preset key.

• Press Peak WL.

3 To move the cursor to view other signals, press:

• PREV WL to select next (previous) shorter wavelength.

• NEXT WL to select next longer wavelength.

• PEAK to signal with greatest power.

• PREV PK to select next lower power signal.

• NEXT PK to select next higher power signal.

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

List by WL or power modes

In the list-by-wavelength or list-by-power modes, the measurements of five laser lines can be displayed at any one time. In list by wavelength mode, the signals are displayed in order from shortest to longest wavelengths. The Agilent 86120B can

measure up to 100 laser lines simultaneously. Use the and softkeys to move the cursor through the list of signals; the list can contain up to 100 entries. Press

the SELECT key, and the display changes to peak wavelength mode with the signal at the cursor displayed.

Annotation in the upper right corner of the display indicates whether the signals are ordered according to wavelength (BY WL) or power (BY PWR). The cursor shows the currently selected laser line. As you scroll through the responses, the current position of the selection cursor is shown along the screen’s right side.

Display after “List by WL” key pressed

Also notice that power bars graphically show the relative power levels between laser lines.

To display multiple laser lines

1 Connect the fiber-optic cable to the front-panel OPTICAL INPUT connector.

2 Press the green Preset key.

3 Press List by WL to display the laser lines from the shortest wavelength to the longest

wavelength.

4 Press List by Power to display the laser lines in order of decreasing amplitudes.

Using the Multi-Wavelength Meter

avg

Piλ

i1=



i1=



--------------------

total

i1=



Displaying Wavelength and Power

Total power and average wavelength

In the third available display mode, the Agilent 86120B displays the average wavelength as shown in the following figure. The displayed power level is the total input power to the instrument. It is the sum of the powers of each laser line; it is not a measure of the average power level of the laser lines.

The following equation shows how individual wavelengths of laser lines are summed together to obtain the average wavelength value:

where,

n is the number of laser lines included in the average. Pi is the peak power of an individual laser line. Power units are in Watts (linear).

The following equation shows how individual powers of laser lines are summed together to obtain the total power value:

where,

n is the number of laser lines included in the measurement. Pi is the peak power of an individual laser line. Power units are in Watts (linear).

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

To display average wavelength and total power

• Press the Avg WL key.

Measuring lasers between 700 nm and 1200 nm

After the Preset key is pressed, the input wavelength range is limited to measuring lasers between 1200 nm and 1650 nm. This prevents the accidental display of spurious signals that may not exist. You can easily expand the input range to the full 700 nm to 1650 nm range, however you should learn how to identify spurious signals.

Spurious signals below 1200 nm may be displayed whenever low-power laser lines (power levels near the Agilent 86120B’s specified sensitivity) are present at the input. For example, a low-power laser line at 1550 nm has a second harmonic line at 775 nm. If this second harmonic is above the peak threshold level relative to the fundamental line, it is considered a peak. Its displayed power level may be greater than that of the fundamental because the amplitude correction at 775 nm is much greater (by about 15 dB) than that at 1550 nm (the interferometer is less sensitive at 775 nm).

You can also avoid displaying this second harmonic line by reducing the peak threshold below its preset value. Because the peak threshold level is used to determine which signals are to be displayed before amplitude corrections are applied, the harmonic will be eliminated. Refer to “Defining Laser-Line Peaks” on page 52.

To use the full wavelength range

1 Press the Setup key.

2 Press the WL LIM softkey.

3 Press LIM OFF to remove the limits on wavelength range. All responses in the full

700 nm to 1650 nm range are now displayed.

Limiting the wavelength range

The wavelength range of measurement can be limited with the wavelength limit function. Both start and stop wavelengths can be chosen. The units of wavelength start and stop are the same as the currently selected wavelength units. If wavelength

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

units are later changed, the start and stop wavelength units will change accordingly. Note that a start wavelength limit in nm will become a stop wavelength limit if THz

-1

or cm

is chosen. See “To change the units of measure” on page 49.

The wavelength limit can be useful when laser modulation causes spurious wavelengths to be displayed. Reducing the wavelength range to the region of interest minimizes the number of spurious wavelengths displayed. Also, the graphical display uses these start and stop wavelength values to plot the power spectrum, whether the wavelength limit function is on or off.

Preset will turn the wavelength limit on and will set the start wavelength to 1200 nm and the stop wavelength to 1650 nm.

To limit the wavelength range

1 Press the Setup key.

2 Press the WL LIM softkey.

3 Press the LIM ON softkey if it is not already highlighted.

4 Press the STARTWL softkey to adjust the start wavelength value.

5 Press the STOP WL softkey to adjust the stop wavelength value.

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

Measuring broadband devices and chirped lasers

When first turned on (or the green Preset key is pressed), the Agilent 86120B is configured to measure narrowband devices such as DFB lasers and modes of FP lasers. If you plan to measure broadband devices such as LEDs, optical filters, and chirped lasers, use the Setup menu first to reconfigure the instrument. When broadband devices are selected, the display shows the BROAD annotation on the screen.

The measurement algorithm for broadband devices determines the wavelength based upon the center-of-mass of the power spectrum. The is used to determine the value of the integration limits. Care must be taken to ensure that the integration limits are above any noise. This is especially true when measuring devices with sloping noise floors, like an EDFA amplifier. For more information on peak excursion, refer to “Defining Laser-Line Peaks” on page 52.

Instrument specifications apply when the Agilent 86120B is configured to measure narrowband devices. Specifications do not apply when the instrument is configured to measure broadband devices.

This feature applies to Agilent 86120B instruments with firmware version number

2.0. When first turned on, the instrument briefly displays the firmware version. Instruments with a firmware version number less than 2.0 do not have this fea ture.

peak excursion function

To measure broadband devices

1 Press the Setup key.

2 Press MORE twice, and then the DEVICE softkey.

3 Press the BROAD softkey.

To return to measuring narrowband devices, press NARROW.

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

Graphical display of optical power spectrum

A graphical display of optical power versus wavelength is shown from the start wavelength value to the stop wavelength value. The start wavelength value is shown in the upper left corner of the graphical display, and the stop wavelength value is shown in the upper right corner of the graphical display. The power scale is a fixed dB scale, with +10 dBm at the display top and –53 dBm at the display bottom. The power scale is not affected by the Power Offset value. In most cases, the noise floor will be visible if the total input power is greater than about –5 dBm.

The Agilent 86120B graphical display.

The Peak Threshold value is displayed as a dotted line. All peaks above this dotted line are displayed in the List by Wavelength and List by Power modes. All peaks below this line are not displayed. Adjust the Peak Threshold value with the Setup key, and the THRSHLD softkey.

The wavelength limit start and stop wavelength values are used for the graphical display even if the wavelength limit function is off.

The graphical display cannot be printed.

To see the graphical display

1 Press the List by WL or List by Power key.

2 Press the GRAPH softkey.

3 To exit the graphical display, press any softkey.

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

Instrument states

Four different instrument states can be saved and recalled at a later time. The actual instrument conditions that are saved are identical to those saved from the previous state after power is turned on. These conditions are shown in Table 8-23 on

page 8-244. If drift measurements or an application (such as signal-to-noise) is on

when an instrument state is saved, it is off when that state is recalled.

To save an instrument state

1 Press the Setup key.

2 Press the SAV/RCL softkey.

3 Press the SAVE softkey.

4 Press one of the four SAVE softkeys to save the instrument state.

To recall a state

1 Press the Setup key.

2 Press the SAV/RCL softkey.

3 Press the RECALL softkey.

4 Press one of the four RCL softkeys to recall an instrument state.

Power bar

To control the power bar

1 Press the Setup key.

2 Press MORE twice, and then PWR BAR.

3 Press BAR ON to display the power bar, and press BAR OFF to hide the power bar

display.

Using the Multi-Wavelength Meter

Changing the Units and Measurement Rate

This section includes step-by-step instructions for changing the units and measurement rate.

This section includes:

Displayed units 49 Measurement rate 50 Continuous or single measurements 51

Displayed units

As described below, it’s easy to change the wavelength and amplitude units. You can choose between the following units:

Table 2-4. Available Units

Wavelength Power

nm dBm

–

THz

To change the units of measure

1 Press Setup.

2 Press the MORE softkey.

3 Press the UNITS softkey.

μW

Using the Multi-Wavelength Meter

Changing the Units and Measurement Rate

4 Press WL and select one of the following units. Then, press RETURN to complete

your selection:

• NM for nanometers

• THZ for terahertz

• CM –1 for wave number

5 Press POWER and select one of the following units:

• DBM for decibels relative to a milliwatt

• MW for milliwatts

• UW for microwatts

Measurement rate

Under normal operation, the Agilent 86120B makes a measurement and displays the results about once every second. It is in this normal update mode that maximum accuracy and wavelength resolution are achieved. However, should a faster update be desired, for example when real-time feedback is required to tune a laser to its designated channel, the Agilent 86120B can be set to update approximately three times per second. This reduces both wavelength resolution and accuracy but can be beneficial in some applications.

When FA S T update is selected, one less digit of resolution is displayed. Also, if multiple wavelengths are present, these individual responses, with the reduced resolution, may no longer be recognized.

To change the measurement speed

1 Press the Setup key.

2 Press the MORE softkey.

3 Press the UPDATE softkey.

4 Select either NORMAL or FA S T .

Using the Multi-Wavelength Meter

Changing the Units and Measurement Rate

Continuous or single measurements

The Agilent 86120B continuously measures the input spectrum at the front-panel OPTICAL INPUT connector. Whenever measurements are being acquired, an asterisk (*) is displayed in the display’s upper right corner. When you switch between normal and fast update modes the rate that the asterisk blinks changes.

You can specify that the instrument perform a measurement only when the frontpanel Single key is pressed. This is the single-acquisition measurement mode, and it is useful for capturing and preserving data. After capturing the data, you can display it using many of the procedures included in this chapter. You can return to continuous measurement mode at any time by pressing the Cont key.

To select single measurement acquisition

• Press the Single key.

Using the Multi-Wavelength Meter

8 dBm– 2 dBm 10 dB –=()

Defining Laser-Line Peaks

The Agilent 86120B uses two rules to identify valid laser-line peaks. Understanding these rules is essential to getting the most from your measurements. For example, these rules allow you to “hide” AM modulation sidebands or locate laser lines with small amplitudes.

In order to identify a laser line, the laser-line must meet both of the following rules:

• Power must be greater than the power established by the peak threshold limit

• Power must rise and then fall by at least the peak excursion value

In addition, the input wavelength range can be limited as described in this section.

Peak threshold limit The peak threshold limit is set by subtracting the peak threshold value from the

power of the largest laser line. So, if the largest laser line is 2 dBm and the peak threshold value is 10 dB, the peak threshold limit is –8 dBm

. You can set the peak threshold value between 0 to 40

dB.

The peak threshold’s default value is 10 dB. This ensures that any modulated signals being measured are not confused with their AM sidebands. For unmodulated lasers, or Fabry-Perot lasers, it may be desirable to increase this threshold to look for responses that are more than 10 dB from the peak.

Peak threshold can be used to suppress spurious signals. For example, a laser that is amplitude modulated in the audio frequency range can cause spurious wavelengths to be displayed below and above the correct wavelength. The power of these spurious wavelengths is below that of the correct wavelength. These spurious signals can be eliminated by decreasing Peak threshold from its Preset value.

Peak excursion The peak excursion defines the rise and fall in amplitude that must take place in

order for a laser line to be recognized. The rise and fall can be out of the noise, or in the case of two closely spaced signals, out of the filter skirts of the adjacent signal. The peak excursion’s default value is 15 dB. Any laser line that rises by 15 dB and then falls by 15 dB passes the rule. You can set the peak excursion value from 1 to 30 dB.

Using the Multi-Wavelength Meter

Defining Laser-Line Peaks

Examples of valid and invalid signals

In the following figure, three laser lines are identified: responses 1, 3, and 4. Response ¡ is not identified because it is below the peak threshold. The portion of each signal that is within the peak excursion limits is shown in bold lines.

Because of the peak excursion rule, responses 4 and 5 are identified as one laser line—the minimum point between 4 and 5 does not drop to the peak excursion limit. This response has the highest power shown which is peak 4.

Whenever the peak threshold limit or peak excursion value is changed, the new limits are applied to the current displayed measurements even if the instrument is in the Single measurement mode.

The following figure shows the same laser lines as the previous figure, but the peakexcursion value has been changed from 15 to 3 dB. Four laser lines are now identified with responses Ð and ƒ identified as two distinct laser lines.

Using the Multi-Wavelength Meter

Defining Laser-Line Peaks

Limiting the input wavelength range

The Agilent 86120B’s preset condition limits the wavelength measurement range from 1200 nm to 1650 nm. You can expand the wavelength range to cover the entire 700 nm to 1650 nm range. Although wavelength range limiting reduces the number of laser lines found, its main purpose is to eliminate the identification of second harmonic distortion products as described in the following sidebar.

Distortion caused by low-power laser lines

Low-power laser lines (power level near the Agilent 86120B’s specified sensitivity) may be accompanied by second harmonic (or other) distortion. For example, a low-power laser line at 1550 nm has a second harmonic line at 775 nm. If this second harmonic is above the peak threshold level relative to the fundamental line, it is considered a peak. Its displayed power level may be greater than that of the fundamental because the amplitude correction at 775 nm is much greater (by about 15 dB) than that at 1550 nm (the interferometer is less sensitive at 775 nm).

To avoid displaying this second harmonic line, limit the input wavelength range from 1200 nm to 1650 nm.

Or, reduce the peak threshold below its preset value. Because the peak threshold level is used to determine which signals are to be displayed before amplitude corrections are applied, the harmonic will be eliminated.

To define laser-line peaks

1 Press the Setup key.

Using the Multi-Wavelength Meter

Defining Laser-Line Peaks

2 Press the THRSHLD softkey.

3 Press PX EXC, and enter the peak excursion value. Use the softkey to select the

digit that requires editing. Use the and softkeys to change the value.

The peak excursion value can range from 1 to 30 dB. The default value is 15 dB.

4 Press RETURN.

5 Press PK THLD and then enter the peak threshold value.

The peak threshold value can range from 0 to 40 dB. Setting this value to 0 dB ensures that only the peak wavelength is identified. The default value is 10 dB.

Pressing the green PRESET key changes the peak excursion and peak threshold values to their default settings. It also turns wavelength range limiting on. Turning the Agilent 86120B’s power off and then on does not change these settings.

If too many lines are identified

If the following message is displayed, too many laser lines have been identified:

E15 MAX NUMBER OF SIGNALS FOUND

The maximum number of laser lines that the instrument can measure is 100. If this message appears, decrease the peak threshold value, increase the peak excursion value, or decrease the wavelength range of operation with the WL

LIM ....START WL and STOP WL functions.

Using the Multi-Wavelength Meter

Measuring Laser Separation

It is often important to measure the wavelength and power separation between multiple laser lines. This is especially true in wavelength-division-multiplexed (WDM) systems where channel spacing must be adhered to. The Agilent 86120B can display the wavelength and amplitude of any laser line relative to another. In fact, the following types of relative measurements can be made compared to the reference:

• Relative wavelength, absolute power

• Relative power, absolute wavelength

• Relative wavelength and power

This section includes:

Channel separation 57 Measuring flatness 58

Using the Multi-Wavelength Meter

Measuring Laser Separation

Channel separation

Suppose that you want to measure separation on a system having the spectrum shown in the following figure.

The Agilent 86120B displays separation on this spectrum as shown in the following figure. Notice that the 1541.747 nm laser line is selected as the reference. It is shown in absolute units. The wavelengths and powers of the remaining responses are shown relative to this reference. For example, the first response is 2.596 nm below the reference.

To determine channel spacing, simply read the relative wavelength measurement of

the laser lines immediately preceding and following the reference. Use the , , and SELECT softkeys to change the reference laser line and read the channel spacing between each channel.

To measure channel separation

1 Press the front-panel Preset key.

Using the Multi-Wavelength Meter

Measuring Laser Separation

2 Press List by WL.

3 Press the Delta On key.

Use the Off key to turn off the measurement.

4 Select the type of separation to observe:

• Δ WL displays channel separation.

• Δ WL / Δ PWR displays both channel separation and differences in power.

5 Use the and softkeys to select the reference laser line.

6 Press SELECT.

Press SELECT at any time to select a new reference. Press RESET at any time to turn off the delta calculation.

Measuring flatness

You can use relative power measurements to measure flatness (pre-emphasis) in a WDM system. Simply select one carrier as the reference and measure the remaining carriers relative to the reference level. The power differences represent the system flatness. Press RESET to turn off the delta calculations so that all responses are shown in absolute wavelength and powers.

Using the Multi-Wavelength Meter

Measuring Laser Separation

To measure flatness

1 Press the front-panel Preset key.

2 Press List by Power.

This lists the input signals by power with the largest response listed first.

3 Press the Delta On key.

4 Select Δ PWR.

5 Use the and softkeys to select the first laser line.

6 Press SELECT.

7 Since the largest power signal is the reference, the relative power measurements for

the other responses shows system flatness.

Using the Multi-Wavelength Meter

spacing 6

10–

×10 Fλ

Measuring Modulated Lasers

Lasers modulated at low frequencies

A laser that is amplitude modulated at low frequencies (for example, modulated in the audio frequency range) can cause spurious wavelengths to be displayed below and above the correct wavelength. The power of these spurious wavelengths is below that of the correct wavelength. These spurious signals can be eliminated by decreasing the peak threshold. Refer to “Defining Laser-Line Peaks” on page 52. Even when the laser is amplitude modulated, the correct wavelength and power is displayed.

The spurious wavelengths caused by low frequency amplitude modulation will be located above and below the correct wavelength by the following wavelength spacing:

where F is the modulation frequency in Hz, and λ is the correct wavelength in nm. For example, an amplitude modulation of 10 kHz on a 1550 nm laser will produce spurious wavelengths spaced by 15 nm from the correct wavelength, and the spurious wavelengths will be at 1535 and 1565 nm.

Low frequency (10 kHz) AM modulation graph showing rounded sideband spurs.

Using the Multi-Wavelength Meter

Measuring Modulated Lasers

The graphical display is useful for locating these spurious wavelengths. Their amplitude will be below that of the correct wavelength and they will be broad, rounded peaks compared to the sharp peak of the correct wavelength. Use the Peak Threshold function to place the dotted line above the spurious peaks so they will not be displayed in the List by WL or List by Power table.

Lasers modulated at high frequencies

A laser modulated at high frequency (in the RF or microwave range) can also cause spurious wavelengths to be displayed, especially when the modulation is of a repetitive nature such as that of PRBS or SONET digital formats. In general, no spurious wavelengths will be displayed using preset instrument conditions. The preset condition includes peak excursion, peak threshold, and wavelength range limiting. However, increasing peak threshold can cause spurious wavelengths to be displayed. To control the wavelength range, refer to “” on page 44.

Even when the laser being tested is modulated with repetitive formats, the carrier’s correct wavelength and power is displayed; the wavelength and power of the spurious sidebands are incorrect.

The graphical display is useful to see the effects of high frequency modulation. Without modulation, the noise floor is typically 45 dB below the laser power. In general, high frequency modulation will raise the noise floor to about 25 dB below the laser power. The noise floor is typically flat, or white. The actual level of the noise floor depends on the type of data format and the data rate.

Directly modulated lasers

PRBS modulation graph showing raised noise floor.

Directly modulated lasers exhibit a linewidth that is broadband. To measure directly modulated lasers, refer to “Measuring broadband devices and chirped lasers” on

page 46.

Using the Multi-Wavelength Meter

Measuring Total Power Greater than 10 dBm

The maximum total power that can be measured by the Agilent 86120B is 10 dBm. However, with the addition of an external attenuator, more power can be applied. This may be necessary at the transmit end of a wavelength-division-multiplexed system where large signal levels are present. By entering an amplitude offset equal to the amount of attenuation at the instrument’s input, accurate amplitude measurements are shown on the display. Additional amplification can also be accounted for.

To measure total power exceeding 10 dBm

CAUTION The maximum total input power that can be applied to the Agilent 86120B

before damage occurs is 18 dBm. The maximum total input power that can be measured is 10 dBm.

1 Connect an optical attenuator between the front-panel OPTICAL INPUT connector

and the fiber-optic cable.

The attenuator must reduce the total input power to the Agilent 86120B so that it is below +10 dBm.

2 Press Setup, MORE, CAL, and then PWR OFS.

Notice that the PWR OFS annotation appears on the screen to indicate an offset is applied.

3 Use the softkey to select the digit that requires editing.

4 Use the and softkeys to change the value.

Power offset values are added to the display power readings. For example, if you placed a 10 dB attenuator on the front-panel connector, enter a power offset value of +10 dB. Negative values can also be entered if you connect an amplifier instead of an attenuator.

Using the Multi-Wavelength Meter

Calibrating Measurements

The wavelength of light changes depending on the material that the light is passing through. To display meaningful wavelength measurements, the Agilent 86120B performs two steps:

1 Measures the wavelength in air.

2 Converts the wavelength to show values in either a vacuum or “standard air”.

For example, a laser line with a wavelength of 1550.000 nm in a vacuum would have a wavelength in standard air of 1549.577 nm.

Because all measurements made inside the Agilent 86120B are performed in air, the density of air, due to elevation, affects the wavelength results. You must calibrate the Agilent 86120B by entering the elevation. Elevations from 0 to 5000 meters can be entered. The elevation correction is immediately applied to the current measurement even if the instrument is in the single measurement acquisition mode.

Annotation on the display shows the current calibration elevation in meters and whether the wavelength measurements are shown for a vacuum (VAC) or standard air (STD AIR).

If you select frequency instead of wavelength measurements, switching between vacuum and standard air will not affect the measurement results. This is because the frequency of an optical signal does not change in different mediums—only the wavelength changes.

Definition of standard air

Standard air is defined to have the following characteristics:

Barometric pressure: 760 torr Temperature: 15⋅C Relative humidity: 0%

To enter the elevation

1 Press the Setup key.

2 Press the MORE softkey.

Using the Multi-Wavelength Meter

3.281

-------------

Calibrating Measurements

3 Press the CAL softkey.

4 Press ELEV.

5 Use the and softkeys to enter the elevation in meters. Entries jump in 500

meter steps from 0 m to 5000 m.

In order for the Agilent 86120B to meet its published specifications, the elevation value selected with the softkeys must be within 250 meters of the actual elevation.

6 Press RETURN to complete the entry.

Converting feet to meters

If you know your elevation in feet, you can convert this value to meters by using the following equation:

To select the medium for light

1 Press the Setup key.

2 Press the MORE softkey.

3 Press the CAL softkey, and make the following selection:

• Press VAC UUM for wavelengths in a vacuum.

• Press STD AIR for wavelengths in standard air.

4 Press RETURN to complete the entry.

Using the Multi-Wavelength Meter

Printing Measurement Results

Measurement results can be sent directly to a printer. Simply connect a compatible printer to the rear-panel PARALLEL PRINTER PORT connector. The output is ASCII text. An example of a compatible printer is Hewlett-Packard series printer. Be sure to use a parallel printer cable to connect the printer.

The printer output is not a copy of the display. Rather, it is a listing of all signals present at the input (up to 100). The measurement values printed depend on the settings of the instrument when the Print key is pressed.

The following is an example of a typical printout:

Agilent 86120B SER US36151025 Firmware Ver. 2.000 List By Wavelength 8 Lines Power Offset 0.0 dB Vacuum Elevation 0 Meters Update Normal Peak Excursion 15 dB Peak Threshold 10 dB Device Narrow

’s L ase rJet1

Input Wavelength Power

----------- ----------

1280.384nm -16.97dBm

1281.473 -13.14

1282.569 -13.92

1283.651 -13.34

1284.752 -11.69

1285.840 -8.11

1286.944 -10.38

1288.034 -14.65

To create a hardcopy

1 Connect the printer to the Agilent 86120B’s rear-panel PARALLEL PRINTER

PORT connector.

2 Press Print.

1. Hewlett-Packard and LaserJet are registered trademarks of Hewlett-Packard Company.

You can use the ABORT and CONT softkey to stop and restart a print job that is in progress.

Measuring Signal-to-Noise Ratios 69 Measuring Signal-to-Noise Ratios with Averaging 73 Measuring Laser Drift 75 Measuring Coherence Length 78

Measurements Applications

In this chapter, you’ll learn how to make a variety of fast, accurate measurements using the measurement tools accessed by pressing the Appl’s key.

Measurements Applications

Measuring Signal-to-Noise Ratios

Signal-to-noise measurements provide a direct indication of system performance. Signal-to-noise measurements are especially important in WDM systems because there is a direct relation between signal-to-noise and bit error rate. The Keysight 86120B displays signal-to-noise measurements in the third column. For example, the selected signal in the following figure has a signal-to-noise ratio of

30.0 dB.

Signal-to-noise display.

During a signal-to-noise measurement, the absolute power of the carrier, in dBm, is compared to the absolute power of the noise at the carrier wavelength. See the following figure. The noise power at the carrier must be determined by interpolation because the carrier, in most cases, can not or should not be turned off.

You can select one of two methods used to determine the wavelength where the noise is measured: automatic interpolation or a user-entered wavelength. In the figure above, notice that “S/N AUTO” is displayed to indicate that automatic interpolation is selected.

Measurements Applications

Measuring Signal-to-Noise Ratios

Location of noise measurements

Automatic interpolation

When the signal-to-noise “auto” function is selected, the Keysight 86120B first determines the proximity of any adjacent signal. If the next closest signal is ≤200 GHz (approximately 1.6 nm at 1550 nm) away from the signal of interest, then the noise power is measured half way between the two channels and an equal distance to the other side of the signal of interest. See points P

and Pn2 in the following fig-

ure.

If the closest signal is more than 200 GHz from the signal of interest, or if there is no other signals present, then the noise power is measured at 100 GHz on either side of the signal of interest. The two measured noise power levels are then averaged to estimate the noise power level at the signal wavelength. The noise power measurements use linear interpolation to estimate the noise power level at the signal of interest’s wavelength.

Automatic interpolation

Measurements Applications

Measuring Signal-to-Noise Ratios

User-entered wavelength

When the signal-to-noise “user” function is selected, the Keysight 86120B uses only one wavelength to measure the noise power for all signals. This wavelength is set by the user and all signals are compared to the noise level at this wavelength to determine their corresponding signal-to-noise ratios.

Noise bandwidth When measuring noise power, the Keysight 86120B must account for the noise

bandwidth used during the measurement. Because noise bandwidth varies with measurement bandwidth (a wide bandwidth allows more noise to the Keysight 86120B’s detector than a narrow bandwidth), the Keysight 86120B normalizes all noise power measurements to a bandwidth of 0.1 nm. The annotation 0.1 nm is displayed to show that the noise bandwidth is being normalized to a 0.1 nm bandwidth.

Repetitive data formats

The Keysight 86120B signal-to-noise application works best when the laser being tested is not modulated, or modulated with non-repetitive data formats. With repetitive data formats, such as PRBS data and SONET formats, there is significant low-frequency amplitude modulation of the laser. This modulation raises the noise floor of the Keysight measured can be limited to about 15

86120B significantly. The signal-to-noise

dB while measuring lasers modulated by repetitive data formats. For improved performance when the laser is modulated with repetitive data formats, use the Signal-to-Noise with Averaging applica

tion.

To measure signal-to-noise

1 Press the front-panel Preset key.

2 Press List by WL or List by Power.

3 Press Appl’s and then S/N.

Measurements Applications

Measuring Signal-to-Noise Ratios

4 To select the wavelength reference for measuring the noise, do the following steps:

a Press WL REF, and

•press AUTO to let the instrument interpolate the wavelength,

•press USER to select the last wavelength manually entered.

b If you chose USER, you can specify the wavelength by pressing USER WL. Use

the

softkey to select the digit that requires editing. Use the and softkeys

to change the value.

c Press RETURN.

5 While the signal-to-noise measurements are displayed, you can press PEAK anytime

to select the signal with the highest power.

Measurements Applications

Measuring Signal-to-Noise Ratios with Averaging

When the lasers being measured are modulated, especially with repetitive data formats such as SONET or PRBS, the noise floor is raised. Averaging reduces the noise floor and allows an improvement of greater than 10 dB in a signal-to-noise measurement. In general, averaging will decrease the noise floor caused by modulation until the true optical noise level is reached. The displayed signal-to-noise will improve with each average until the true optical noise level is reached, and then the displayed signal-to-noise will remain approximately constant. If, however, the true signal-tonoise is below the instrument sensitivity of approximately 40 dB (in a 0.1 nm noise bandwidth), it will not be measured.

Averaging can also improve the accuracy of measuring signal-to-noise of unmodulated lasers.

Signal-to-noise with averaging display.

Averaging is performed on the noise, not on the wavelength or power of the laser signals.

The signal-to-noise with averaging measurement uses the automatic interpolation method to determine the wavelengths where the noise is measured. Refer to “Mea-

suring Signal-to-Noise Ratios” on page 69 for a description of automatic interpola-

tion. There is no user-entered wavelength selection in signal-to-noise with averaging.

During a signal-to-noise with averaging measurement, the display indicates S/N A xx, where A indicates averaging and xx is the number of averages taken so far. The maximum number of averages is 900, the minimum number of averages is 10, and the default (Preset) value is 100 averages. A measurement with 100 averages takes about 2 minutes to complete. When the measurement is complete, the instrument switches to single measurement mode. Then, pressing the Cont key will start a

Measurements Applications

Measuring Signal-to-Noise Ratios with Averaging

completely new measurement. During a measurement and before the number of averages has been reached, pressing the Single key will stop the measurement. Then, pressing the Cont key will continue with the current measurement.

While making a signal-to-noise with averaging measurement, the number of averages can be changed. As long as the new number of averages is greater than the number of averages taken so far, the measurement continues. If the new number of averages selected is less than the number of averages taken so far, the measurement stops and the instrument switches to single measurement mode. Then, pressing the Cont key will start a completely new measurement.

Noise bandwidth affects measurement

When measuring noise power, the Keysight 86120B must account for the noise bandwidth used during the measurement. Because noise bandwidth varies with measurement bandwidth (a wide bandwidth allows more noise to the Keysight 86120B’s detector than a narrow bandwidth), the Keysight 86120B normalizes all noise power measurements to a bandwidth of 0.1 nm. The annotation 0.1 nm is displayed to show that the noise bandwidth is being normalized to a 0.1 nm bandwidth.

To measure signal-to-noise with averaging

1 Press the front panel Preset key.

2 Press List by WL or List by Power.

3 Press Appl's and then S/N AVG.

4 To change the number of averages, press NUM AVG. The default (Preset) value is

100.

5 To stop the measurement at the current number of averages shown, press the Single

key. Then press the Cont key to continue the present measurement.

6 When the measurement is complete, the instrument will switch to the single

measurement mode and stop.

7 To make a new measurement, press the Cont key.

8 To exit, press the EXIT softkey, then press the Cont key for continuous measurement.

Measurements Applications

Measuring Laser Drift

In this section, you’ll learn how the Keysight 86120B can be used to monitor drift (changes to a laser’s wavelength and amplitude over time). Drift is measured simultaneously for every laser line that is identified at the input. The Keysight 86120B keeps track of each laser line’s initial, current, minimum, and maximum values and displays their differences relative to itself. This allows the Keysight 86120B to be used for laser transmitter evaluation, burn-in, or development. In addition, you can monitor system performance over time, temperature, or other condition.

The following display shows power and wavelength drift measured on five laser lines. The DRIFT annotation, item ¿, tells you that drift measurements are being performed. The current relative drift values for wavelength and power are shown in items ¡ and ¬ respectively. Item Ð indicates the absolute reference values for the

laser line indicated by the cursor . The reference values are measured before the measurement starts.

You can restart the drift measurement at any time by pressing the RESET softkey. All minimum and maximum values are reset to the reference values, and the Keysight 86120B begins to monitor drift from the current laser line values. Move the cursor up and down the listing to see the reference wavelength and power of each laser line.

Measurements Applications

Measuring Laser Drift

If measurement updating stops or the values become blanked

If, in the middle of a measurement, the number of laser lines present changes, the measurement stops until the original number of lines returns. You’ll notice that a CLEAR softkey appears and one of the following message is displayed:

E46 NUM LINES < NUM REFS E47 NUM LINES > NUM REFS

To view the data measured before the conditions changed, press CLEAR and then MAX-MIN. Notice that the measurement acquisition is changed from con tinuous to single.

To restart testing, press CLEAR, the CONT key, and then RESET to use the new number of lines as the reference. Pressing CONT restarts continuous mea surement acquisition. Or, you can restore the original number of lines on the input so that the drift measurement can continue.

To measure drift

1 Press the front-panel Preset key.

2 Press Peak WL, List by WL, or List by Power to select the display style for observing

drift.

3 Press Appl’s and then DRIFT.

Pressing DRIFT sets the current laser-line values as the reference from which to compare all drift.

4 Press MAX-MIN for the desired type of drift measurement as described in the

following paragraphs:

Display shows the current values of laser lines relative to the

wavelength and power values measured when the test was begun or the RESET softkey was pressed.

Display shows absolute maximum values since the drift

measurement was started. This measurement gives the longest wavelength and greatest power measured. The laser line of interest may have since drifted to a lesser value. Note that the maximum wavelength and maximum power may not have occurred simultaneously.

Display shows absolute minimum values since the drift

measurement was started. This measurement gives the shortest

Measurements Applications

Measuring Laser Drift

wavelength and smallest power measured. The laser line of interest may have since drifted to a greater value. Note that the minimum wavelength and minimum power may not have occurred simultaneously.

Display shows the total drift from the reference since the drift

measurement was started. Values represent the minimum wavelength and power drift values subtracted from the maximum drift values.

5 In the List by WL and List by Power displays, use the and softkeys to view

the reference values (wavelength and power values of each laser line before the test was started).

During the measurement, you can change the display mode to Peak WL, List by WL, List by Power, or Avg WL. When List by WL or List by Power is selected, the signal list is sorted by reference values and not by the current, maximum, or minimum val ues.

To restart the drift measurements, press RESET. This resets the reference values.

Measurements Applications

Measuring Coherence Length

Coherence length is a measure of the distance over which a laser’s light retains the phase relationships of its spectrum. The Keysight 86120B measures coherence length of Fabry-Perot semiconductor diode lasers. The Keysight 86120B cannot measure coherence length of light emitting diodes (LEDs) or distributed feedback (DFB) lasers.

When you select coherence length measurements, the Keysight 86120B displays the following four values:

• Coherence length (Lc)

• Round trip optical length of diode laser cavity (2nLd)

• Alpha factor

• Beta factor

Coherence length in the region of 1 mm to 200 mm can be measured. The following figure shows a coherence length measurement.

To measure coherence length

1 Press the front-panel Preset key.

2 Press Appl’s and then COH LEN.

Measurements Applications

decay curve e

OPD

------------

–

1e⁄

Measuring Coherence Length

Coherence length (L

)

The interferogram of the laser being tested is sampled and the envelope of the interferogram is found. This envelope has peaks (regions of high fringe visibility) at zero optical path delay and at delays equal to multiples of the laser cavity round-trip optical length. This is shown in the following figure of the interferogram envelope:

The amplitudes of the peaks decreases exponentially from the largest peak at zero path delay. The exponential decay constant is defined as the coherence length, Lc. The curve that connects the tops of the envelope peaks is given by the following equation:

OPD is the optical path delay and Lc is the coherence length. Thus, at an optical path delay equal to the coherence length, the envelope peaks are down to of their value at zero path delay peak. All envelope peaks found are used to determine

the exponential decay constant (coherence length) using a least squares fit.

Round trip optical length of diode laser

The average optical path delay spacing of the envelope peaks is measured. This is equal to the diode laser cavity round trip optical length, 2nLd.

cavity (2nLd)

Alpha factor The alpha factor is defined as the height of the first envelope peak away from zero

path delay relative to the height of the envelope peak at zero path delay. The alpha factor is always between 0 and 1.

Measurements Applications

Alpha factor

------

Beta factor

------

Measuring Coherence Length

The smaller the alpha factor, the shorter the coherence length.

Beta factor The beta factor is defined as the height of the fringe visibility envelope midway

between the zero optical path delay peak and the next peak relative to the height of the envelope peak at zero path delay. The beta factor is always between 0 and 1.

The smaller the beta factor, the more longitudinal modes (wavelengths) the laser has.

Addressing and Initializing the Instrument 83

To change the GPIB address 83

Making Measurements 85

Commands are grouped in subsystems 87 Measurement instructions give quick results 89 The format of returned data 95

Monitoring the Instrument 96

Status registers 96

Queues 101 Reviewing SCPI Syntax Rules 103 Example Programs 108

Example 1. Measure a DFB laser 110

Example 2. Measure WDM channels 112

Example 3. Measure WDM channel drift 114

Example 4. Measure WDM channel separation 117

Example 5. Measure SN ratio of WDM channels 119

Example 6. Increase a source’s wavelength accuracy 121 Lists of Commands 123

Programming

This chapter explains how to program the Keysight 86120B. The programming syntax conforms to the IEEE 488.2 Standard Digital Interface for Programmable Instrumentation and to the Standard Commands for Programmable Instruments (SCPI).

Where to begin…

The programming examples for individual commands in this manual are written in

®1

BASIC 6.0 for an HP 9000 Series 200/300 Controller.

For more detailed information regarding the GPIB, the IEEE 488.2 standard, or the SCPI standard, refer to the following books:

Hewlett-Packard Company. Tutorial Description of Hewlett-Packard Interface Bus,

1987.

Hewlett-Packard Company. SCPI—Standard Commands for Programmable Instru- ments, 1995.

International Institute of Electrical and Electronics Engineers. IEEE Standard 488.1- 1987, IEEE Standard Digital Interface for Programmable Instrumentation. New York, NY, 1987.

International Institute of Electrical and Electronics Engineers. IEEE Standard 488.2-

1987, IEEE Standard Codes, Formats, Protocols and Common commands For Use with ANSI/IEEE Std 488.1-1987. New York, NY, 1987.

Types of commands

The Keysight 86120B responds to three types of commands:

• Common commands

• Measurement instructions

• Subsystem commands

All of these commands are documented in Chapter 5, “Programming Commands”.

1. HP is a registered trademark of Hewlett-Packard Company.

Programming

Addressing and Initializing the Instrument

The Keysight 86120B’s GPIB address is configured at the factory to a value of 20. You must set the output and input functions of your programming language to send the commands to this address.

To change the GPIB address

1 Press the Setup key.

2 Press MORE twice, then GPIB.

3 Use the and softkeys to change the GPIB address.

4 Press RETURN.

Remote mode and front-panel lockout

Whenever the instrument is controlled by a computer, the Remote message is displayed on the instrument’s screen and the softkey menu is blanked except for the LOCAL softkey. This softkey can be pressed by the user to restore front panel control of the instrument.

You can specify a local lockout mode that prevents the LOCAL softkey from being displayed. If the instrument is in local lockout mode, all the softkeys may be blanked. For example, if the instrument is first placed in local lockout mode and then placed in remote mode, no softkeys are displayed.

Consult the documentation for your programming environment to determine which commands are used to put an instrument in the remote and local lockout modes. These are not Keysight 86120B commands; they control GPIB control lines and do not send any characters to the Keysight 86120B.

Initialize the instrument at start of every program

It is good practice to initialize the instrument at the start of every program. This ensures that the bus and all appropriate interfaces are in a known state. HP BASIC provides a CLEAR command which clears the interface buffer and also resets the instrument’s parser. (The parser is the program that reads the instructions that you send.) Whenever the instrument is under remote programming control, it should be

Programming

Addressing and Initializing the Instrument

in the single measurement acquisition mode. This is automatically accomplished when the *RST common command is used. The *RST command initializes the instrument to a preset state:

CLEAR 720 OUTPUT 720;”*RST”

Notice in the example above, that the commands are sent to an instrument address of

720. This indicates address 20 on an interface with select code 7. Pressing the green Preset key does not change the GPIB address.

Set single acquisition mode

An advantage of using the *RST command is that it sets the Keysight 86120B into the single measurement acquisition mode. Because the READ and MEASure data queries expect this mode, their proper operation is ensured.

Establish the wavelength range

At the start of each program, be sure to establish the input wavelength range using the Keysight 86120B’s :CALCulate2:WLIMit command. Setting this command to off enables the full wavelength range of the instrument. If you are measuring signals over a narrow wavelength range, use this command to ensure that spurious second harmonic peaks are not identified. Refer to “WLIMit[:STATe]” on page 166,

“WLIMit:STARt[:WAVelength]” on page 169, and “WLIMit:STOP[:WAVelength]” on page 172. Refer also to “To limit the wavelength range” on page 45.

Programming

Making Measurements

Making measurements remotely involves changing the Keysight 86120B’s settings, performing a measurement, and then returning the data to the computer. The simplified block diagram of the Keysight 86120B shown here lists some of the available programming commands. Each command is placed next to the instrument section it configures or queries data from.

Notice that there are two buffers from which data can be queried: an uncorrected data buffer and a corrected data buffer. With each scan of the input wavelength range, the analog-to-digital converter loads 65,536 data values into the uncorrected data buffer. This is considered to be one “measurement”. A fast-update measurement mode is available for quicker measurement acquisition. But, because only 8,192 data values are collected in fast-update measurement mode, the ability to resolve closely spaced signals is reduced.

After collecting the uncorrected data, the Keysight 86120B searches the data for the first 100 peak responses. (Searching starts at 1700 nm and progresses towards 700 nm for WLIMit OFF. If WLIMit is on, searching starts at WLIMit:STARt to

Programming

Making Measurements

WLIMit:STOP). These peak values are then placed into the corrected data buffer. Each peak value consists of an amplitude and wavelength measurement. Amplitude and wavelength correction factors are applied to this data.

For a listing of the programming commands (including a cross reference to frontpanel keys), refer to the following tables:

Table 4-11, “Programming Commands,” on page 4-123 Table 4-12, “Keys Versus Commands,” on page 4-128

Programming

Making Measurements

Commands are grouped in subsystems

The Keysight 86120B commands are grouped in the following subsystems. You’ll find a description of each command in Chapter 5, “Programming Commands”.

Subsystem Purpose of Commands

Measurement Instructions

CALCulate1 Queries uncorrected frequency-spectrum data.

CALCulate2 Queries corrected peak data and sets wavelength limits.

CALCulate3 Performs delta, drift, and signal-to-noise measurements.

DISPlay Applies markers and displays power bars.

HCOPy Prints measurement results.

SENSe Sets elevation-correction values, selects readings for air or

Perform frequency, wavelength, wavenumber, and coherence length measurements.

vacuum, and enters amplitude offsets. Configures instrument for measuring broadband devices and chirped lasers. Queries time-domain values of the input data.

STATus Queries instrument status registers.

SYSTem Presets Keysight 86120B and queries error messages.

TRIGger Stops current measurement. Acquires new measurement data.

Also used to select single or continuous acquisition of measurement data.

UNIT Sets the amplitude units to watts or dBm.

Table 2-5 on page 4-88 shows the kinds of measurements that the Keysight 86120B

can perform and the associated programming commands used to return that data. In some cases, there is more than one method that can be used to obtain the desired data. Refer to Chapter 5, “Programming Commands” for the correct syntax for these commands.

Programming

Making Measurements

Table 2-5. Commands for Capturing Data

Desired Measurement

Wavelength (nm) CONFigure, FETCh, READ, and

Frequency (THz) CONFigure, FETCh, READ, and

Wavenumber (m–1)

Coherence Length (m) CONFigure, FETCh, READ, and

Power (W, dBm) CONFigure, FETCh, READ, and

Average Wavelength, Wavenumber, or Frequency

Total Power (W, dBm) CALCulate2:PWAVerage:STATe CALCulate2:DATA?

Laser-Line Separation CALCulate3:DELTa:REFerence CALCulate3:DATA?

Laser-Line Drift CALCulate3:DRIFt:STATe CALCulate3:DATA?

Signal-to-Noise Ratio CALCulate3:SNR:STATe CALCulate3:DATA?

Signal-to-Noise Ratio Average CALCulate3:ASNR:STATe CALCulate3:DATA?

Time-Domain Data CALCulate1:TRANsform:FREQuency:P

Corrected Frequency Domain Data

Uncorrected Frequency Domain Data

Command to Configure Measurement (partial listing)

MEASure

CONFigure, FETCh, READ, and MEASure

MEASure

CALCulate2:PWAVerage:STATe CALCulate2:DATA?

OINts

CALCulate1:TRANsform:FREQuency:P OINts

Command to Query Data

MEASure:ARRay:POWer:WAVelen gth?

MEASure:ARRay:POWer:FREQuen cy?

MEASure:ARRay:POWer:WNUMb er?

FETCh, READ, or MEASure

MEASure:ARRay:POWer?

SENSe:DATA?

CALCulate2:DATA?

CALCulate1:DATA?

Measurement instructions give quick results

The easiest way to measure wavelength, frequency, power, or coherence length is to use the MEASure command. The MEASure command is one of four measurement instructions: MEASure, READ, FETCh, and CONFigure. The syntax for measurement instructions is documented in “Measurement Instructions” on page 146.

Each measurement instruction has an argument that controls the measurement update rate. This is equivalent to using the NORMAL and FA S T softkeys.

:MEASure command

MEASure configures the Keysight 86120B, captures new data, and queries the data all in one step. For example, to measure the longest wavelength, send the following command:

:MEASure:SCALar:POWer:WAVelength? MAX

Table 2-6. The Different Forms of MEASure

Programming

Making Measurements

Desired Measurement Data

Power (W, dBm) :MEASure:ARRay:POWer? List by Power

Frequency (Hz) :MEASure:ARRay:POWer:FREQuency? List by WL (frequency)

Wavelength (m) MEASure:ARRay:POWer:WAVelength? List by WL

Wavenumber (m–1)

Coherence Length (m) :MEASure:LENGth:COHerence? coherence length

Use this MEASure Query

:MEASure:SCALar:POWer? single wavelength mode

:MEASure:SCALar:POWer:FREQuency? single wavelength mode

MEASure:SCALar:POWer:WAVelength? single wavelength mode

:MEASure:ARRay:POWer:WNUMber? List by WL

:MEASure:SCALar:POWer:WNUMber? single wavelength mode

Display Format

Specifying SCALar places the display in the single wavelength format and returns a single value to the computer. Specifying ARRay places the display in the List by Power or List by WL modes; an array of data is returned to the computer.

Programming

Making Measurements

A common programming error is to send the :MEASure command when the instrument is in the continuous measurement acquisition mode. Because :MEASure contains an :INIT:IMM command, which expects the single measurement acquisition mode, an error is generated, and the INIT command is ignored.

:READ command

The READ command works like the MEASure command except that it does not configure the instrument’s settings. You can use the CONFigure command to configure the instrument for a particular measurement without returning any data.

The MEASure and READ commands are identical to combining the following commands:

Command Equivalent Commands

:MEASure :ABORt;:CONFigure;:READ

:READ :ABORt;:INITiate:IMMediate;:FETCh

A common programming error is to send the :READ command when the instrument is in the continuous measurement acquisition mode. Because :READ contains an :INIT:IMM command, which expects the single measurement acquisition mode, an error is generated, and the INIT command is ignored.

:FETCh command

The FETCh command returns data from previously performed measurements; it does not initiate the collection of new data. Because FETCh does not configure the instrument or acquire new input data, you can use FETCh repeatedly on the same set of acquired data. For example, use two FETCh commands to return wavelength and then power values for the same measurement. This is shown in the following program fragment:

OUTPUT 720;”:INIT:CONT OFF;” OUTPUT 720;”:CONF:ARR:POW MAX” OUTPUT 720;”:INIT:IMM” OUTPUT 720;”:FETC:ARR:POW?” ENTER 720:powers$ OUTPUT 720;”:FETC:ARR:POW:WAV?” ENTER 720:wavelengths$

In the example above, the data in the power and wavelength arrays are returned in the same order so that powers can be matched to wavelengths.

Also, because new data is not collected, FETCh is especially useful when characterizing transient data.

Programming

Making Measurements

FETCh does not reconfigure the display. For example, if the display is in the Peak WL mode, sending :FETCh:ARRay does not configure the display to the List by WL even though an array of data is returned to the computer.

A common programming error occurs when the :FETCh command is used after an *RST command. This generates error number –230, “Data corrupt or stale”. In this instance, you must send :INIT:IMM after the *RST command and before :FETCh command to capture a new array of measurement data.

:CONFigure command

The CONFigure command changes measurement settings without taking a measurement. The instrument is placed in the List by WL, List by Ampl, Peak WL display, or in the coherence length application.

CONFigure can be queried. The query returns the last configuration setup by the CONFigure command. The instrument returns a string which is the last instrument function sent by a CONFigure command or MEASure query. The returned string is in the short command form. Use caution when using this query, because if any instrument settings were changed since the last CONFigure command or MEASure query these changes may not be included in the returned string.

For example, if the last CONFigure command was

:CONFigure:SCALar:POWer:WAVelength 1300NM, MAX

a CONFigure? query would return a string that is similar to the following line:

“POW:WAV 1.300000e-6,0.01”

The 1300NM and resolution values track the actual instrument settings and input signals. Notice that the quotation marks are part of the returned string.

Return single or multiple measurement values

You can specify whether FETCh, READ, or MEASure returns a single value (SCALar) or multiple values (ARRay). The following example specifies SCALar data which returns a single value.

:MEASure:SCALar:POWer:WAVelength? MAX

Programming

Making Measurements

ARRay and the SCPI standard

According to the SCPI command reference, ARRay command causes an instrument to take multiple measurements. (A <size> parameter indicates the number of measurements to take.) However, the Keysight

86120B’s ARRay command refers to the measurements performed for one measurement sweep; this results in an array of measured signals. Because the <size> parameter does not apply, any <size> parameter sent will be ignored by the instrument. No syntax error will be generated if a <size> parameter is sent.

Always force the Keysight 86120B to wait for non-sequential commands

The Keysight 86120B normally processes its remote programming commands sequentially. The instrument waits until the actions specified by a particular command are completely finished before reading and executing the next command. However, there are a few non-sequential commands where this is not true. Nonsequential commands do not finish executing before the next command is inter- preted.

The following is a list of the Keysight 86120B’s non-sequential commands:

:CALCulate1:TRANsform:FREQuency:POINTs :CALCulate2:PEXCursion :CALCulate2:PTHReshold :CALCulate2:WLIMit:STATe :CALCulate2:WLIMit:STARt:FREQuency :CALCulate2:WLIMit:STARt:WAVelength :CALCulate2:WLIMit:STARt:WNUMber :CALCulate2:WLIMit:STOP:FREQuency :CALCulate2:WLIMit:STOP:WAVelength :CALCulate2:WLIMit:STOP:WNUMber :CALCulate3:SNR:AUTO :SENSe:CORRection:ELEVation :INITiate:CONTinuous :INITiate[:IMMediate]

The following additional commands are also non-sequential commands if CALCulate3:SNR:AUTO is set to OFF:

:CALCulate3:REFerence:FREQuency :CALCulate3:REFerence:WAVelength :CALCulate3:REFerence:WNUMber

The benefit of non-sequential commands is that, in some situations, they can reduce the overall execution times of programs. For example, you can set the peak excursion, peak threshold, and elevation and use a *WAI command at the end to save

Programming

Making Measurements

time. However, non-sequential commands can also be a source of annoying errors. Always use the *OPC query or *WAI command with the non-sequential commands to ensure that your programs execute properly.

For example, suppose that you wanted to set the elevation correction value and then send an :INIT:IMM command. The following programming fragment results in an error –213 “Init ignored”. This occurs because the :ELEVation

command causes

the recalculation of the data which is like sending the :INIT:IMM command. When the actual :INIT:IMM is sent, the error occurs because the command is already in progress.

OUTPUT 720;”:INIT:IMM” OUTPUT 720;”:SENSe:CORRection:ELEVation 1000” OUTPUT 720;”:INIT:IMM”

Use an *OPC? query to ensure that the :ELEVation command has completed as shown in the following lines:

OUTPUT 720;”:INIT:IMM” OUTPUT 720;”:SENSe:CORRection:ELEVation 1000” OUTPUT 720;”*OPC?” ENTER 720;Response$ OUTPUT 720;”:INIT:IMM”

Or, the *WAI command could be used:

OUTPUT 720;”:INIT:IMM” OUTPUT 720;”:SENSe:CORRection:ELEVation 1000” OUTPUT 720;”*WAI?” OUTPUT 720;”:INIT:IMM”

Programming

Making Measurements

Measure delta, drift and signal-to-noise

To select a measurement, use one of the following STATe commands:

CALC3:DELT:POW:STAT (delta power) CALC3:DELT:WAV:STAT (delta wavelength) CALC3:DELT:WPOW:STAT (delta power and wavelength) CALC3:DRIF:STAT (drift) CALC3:SNR:STAT (signal-to-noise ratios) CALC3:ASNR:STAT (signal-to-noise ratio averaging)

If you select a drift measurement, you can additionally select one of the following additional states:

CALC3:DRIF:DIFF:STAT (difference) CALC3:DRIF:MAX:STAT (maximum drift) CALC3:DRIF:MIN:STAT (minimum drift) CALC3:DRIF:REF:STAT (drift reference values)

The :CALCulate3:DRIFt:PRESet command turns off the minimum, maximum, difference, and reference states but leaves the drift state on.

Attempting to turn more than one state on at a time results in a “–221 Settings Con- flict” error.

The *RST and SYSTem:PRESet commands turn all calculations off.

CALCulate3:PRESet turns off any CALCulate3 calculations.

Programming

Making Measurements

The format of returned data

Measurements are returned as strings

All measurement values are returned from the Keysight 86120B as ASCII strings. When an array is returned, the individual values are separated by the comma character.

Determine the number of data points

When a FETCh, READ, or MEASure command is used (with ARRay specified), the first returned value indicates the total number of measurement values returned in the query.

If you use the:CALCulate1:DATA?, :CALCulate2:DATA?, or :CALCulate3:DATA? queries to query data, send the :POINts? query first to determine the number of values returned in the string. The string does not contain a first value which specifies the string length. This is shown in the following example:

OUTPUT 720;”:CALCulate1:POINts?” ENTER 720;Length OUTPUT 720;”:CALCulate1:DATA?” ENTER 720;Result$

Data can be corrected for elevation and vacuum

Normally, the Keysight 86120B provides measurement values calculated for conditions in air at sea level. Use the :SENSe:CORRection:ELEVation command to compensate for air dispersion. Altitudes up to 5000 meters can be entered. Use the :SENSe:CORRection:MEDium command to switch to readings in a vacuum.

Amplitude units

The default amplitude units are dBm. If you need measurements in watts, use the :UNIT:POWer command. When the Keysight 86120B is turned on, the amplitude units are automatically set to the units used before the instrument was last turned off.

Programming

Monitoring the Instrument

Almost every program that you write will need to monitor the Keysight 86120B for its operating status. This includes querying execution or command errors and determining whether or not measurements have been completed. Several status registers and queues are provided to accomplish these tasks.

In this section, you’ll learn how to enable and read these registers. In addition to the information in this section, you should review the commands documented in “Com-

mon Commands” on page 133 and “STATus Subsystem” on page 206.

Status registers

The Keysight 86120B provides four registers which you can query to monitor the instrument’s condition. These registers allow you to determine the following items:

• Status of an operation

• Availability of the measured data

• Reliability of the measured data

All three registers are shown in the figure on the following page and have the following uses:

Status Byte Monitors the status of the other three registers.

Standard Event Status This is the standard IEEE 488.2 register. Contains

bits which indicate the status of the other two regis ters.

OPERation Status Contains bits that report on the instrument’s normal

operation.

QUEStionable Status Contains bits that report on the condition of the sig-

nal.

Programming

Monitoring the Instrument

Status Byte register

The Status Byte Register contains summary bits that monitor activity in the other status registers and queues. The Status Byte Register’s bits are set and cleared by the presence and absence of a summary bit from other registers or queues. Notice in the following figure that the bits in the Standard Event Status, OPERation status, and QUEStionable status registers are “or’d” to control a bit in the Status Byte Register.

If a bit in the Status Byte Register goes high, you can query the value of the source register to determine the cause.

The Status Byte Register can be read using either the *STB? common command or the GPIB serial poll command. Both commands return the decimal-weighted sum of all set bits in the register. The difference between the two methods is that the serial poll command reads bit 6 as the Request Service (RQS) bit and clears the bit which clears the SRQ interrupt. The *STB? command reads bit 6 as the Master Summary Status (MSS) and does not clear the bit or have any effect on the SRQ interrupt. The value returned is the total bit weights of all of the bits that are set at the present time.

OPERation Status and QUEStionable Status registers

You can query the value of the OPERation Status and QUEStionable Status registers using commands in the STATus subsystem.

The STATus subsystem also has transition filter software which give you the ability to select the logic transitions which set bits in the OPERation Status and QUEStionable Status registers. For example, you can define the POWer bit of the QUEStionable Status register to report an event when the condition transitions from false to true. This is a positive transition. You can also specify a negative transition where the bit is set when the condition transitions from true to false.

Programming

Monitoring the Instrument

Keysight Technologies 86120B User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Keysight 86120B Multi-Wavelength Meter

The Keysight 86120B—At a Glance

General Safety Considerations

Getting Started

Step 1. Inspect the Shipment

Step 2. Connect the Line-Power Cable

Step 3. Connect a Printer

Step 4. Turn on the Keysight 86120B

Step 5. Enter Your Elevation

Step 6. Select Medium for Wavelength Values

Step 7. Turn Off Wavelength Limiting

Cleaning Connections for Accurate Measurements

Choosing the Right Connector

Inspecting Connectors

Cleaning Connectors

Returning the Instrument for Service

Preparing the instrument for shipping

Using the Multi-Wavelength Meter

Displaying Wavelength and Power

Peak WL mode

List by WL or power modes

Total power and average wavelength

Measuring lasers between 700 nm and 1200 nm

Limiting the wavelength range

Measuring broadband devices and chirped lasers

Graphical display of optical power spectrum

Instrument states

Power bar

Changing the Units and Measurement Rate

Displayed units

Measurement rate

Continuous or single measurements

Defining Laser-Line Peaks

Measuring Laser Separation

Channel separation

Measuring flatness

Measuring Modulated Lasers

Measuring Total Power Greater than 10 dBm

Calibrating Measurements

Printing Measurement Results

Measurements Applications

Measuring Signal-to-Noise Ratios

Measuring Signal-to-Noise Ratios with Averaging

Measuring Laser Drift

Measuring Coherence Length

Programming

Addressing and Initializing the Instrument

Making Measurements

Commands are grouped in subsystems

Measurement instructions give quick results

Measure delta, drift and signal-to-noise

The format of returned data

Monitoring the Instrument

Status registers