Agilent Technologies 86120B User Manual

Agilent 86120B Multi-Wavelength Meter User’s Guide

Agilent Part No. 86120-90033 Printed in USA February 2000

Agilent Technologies Lightwave Division 1400 Fountaingrove Parkway Santa Rosa, CA 95403-1799, USA (707) 577-1400

Notice.

The information contained in this document is subject to change without notice. Companies, names, and data used in examples herein are fictitious unless otherwise noted. Agilent Technologies makes no warranty of any kind with regard to this material, including but not limited to, the implied warranties of merchantability and fitness for a particular purpose. Agilent 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.

Restricted Rights Legend.

Use, duplication, or disclosure by the U.S. Government is subject to restrictions as set forth in subparagraph (c) (1) (ii) of the Rights in Technical Data and Computer Software clause at DFARS 252.227-7013 for DOD agencies, and subparagraphs (c) (1) and (c) (2) of the Commercial Computer Software Restricted Rights clause at FAR 52.227-19 for other agencies.

Warranty.

This Agilent 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, Agilent Technologies will, at its option, either repair or replace products which prove to be defective. For warranty service or repair, this product must be returned to a service facility designated by Agilent Technologies. Buyer shall prepay shipping charges to Agilent Technologies and Agilent Technologies shall pay shipping charges to return the product to Buyer. However, Buyer shall pay all shipping charges, duties, and taxes for products returned to Agilent Technologies from another country.

Agilent Technologies warrants that its software and firmware designated by Agilent Technologies for use with an instrument will execute its programming instructions when properly installed on that instrument. Agilent Technologies does not warrant that the operation of the instrument, or software, or firmware will be uninterrupted or errorfree.

Limitation of Warranty.

The foregoing warranty shall not apply to defects resulting from improper or inadequate maintenance by Buyer, Buyersupplied 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. Agilent 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. Agilent Technolo-

gies shall not be liable for any direct, indirect, special, incidental, or consequential damages, whether based on contract, tort, or any other legal theory.

Safety Symbols.

CAUTION

The

caution

sign 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.

WAR NING

The

warning

sign 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.

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

ISM1-A

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 charac-

ters 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.

The Agilent 86120B—At a Glance

The Agilent 86120B Multi-Wavelength Meter measures the wavelength and optical power of laser light in the 700-1650 nm wavelength range. Because the Agilent 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 Agilent 86120B

This book directly applies to Agilent 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 “Measuring broadband devices

and chirped lasers” on page 2-10.

Characterize laser lines easily

With the Agilent 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 (

• Signal-to-noise ratios

• Coherence length

wavelength and power

)

iii

The Agilent 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 Agilent 86120B’s display.

CAUTION

The input circuitry of the Agilent 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 Agilent 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 Chap-

ter 5, “Programming Commands” provide all the information you’ll need to

know in order to program the Agilent 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 Agilent 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 Agilent 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 measurements.

Before you connect any fiber-optic cable to the Agilent 86120B, refer to “Cleaning Con-

nections for Accurate Measurements” on page 1-13.

General Safety Considerations

This product has been designed and tested in accordance with IEC Publication 1010, Safety Requirements for Electronic Measuring Apparatus, 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.

Laser Classification: This product is classified FDA Laser Class I (IEC Laser Class 1).

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.

No operator serviceable parts inside. Refer servicing to qualified personnel. To prevent electrical shock, do not remove covers.

There is no output laser aperture

The Agilent 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 radiation exposure.

General Safety Considerations

WARNING

CAUTION

To prevent electrical shock, disconnect the Agilent 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.

This is a Safety Class 1 product (provided with a protective earthing ground incorporated in the power cord). 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.

For continued protection against fire hazard, replace line fuse only with same type and ratings, (type T 0.315A/250V for 100/120V operation and 0.16A/250V for 220/240V operation). The use of other fuses or materials is prohibited. Verify that the value of the linevoltage fuse is correct.

• For 100/120V operation, use an IEC 127 5×20 mm, 0.315 A, 250 V, Agilent part number 2110-0449.

• For 220/240V operation, use an IEC 127 5×20 mm, 0.16 A, 250 V, Agilent Technologies part number 2110-0448.

Before switching on this instrument, make sure that the line voltage selector switch is set to the line voltage of the power supply and the correct fuse is installed. Assure the supply voltage is in the specified range.

CAUTION

This product is designed for use in Installation Category II and Pollution Degree 2 per IEC 1010 and 664 respectively.

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

vii

General Safety Considerations

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.

connect ac power until you have verified the line voltage is correct as

Do not

described in “Line Power Requirements” on page 1-6. Damage to the equipment could result.

This instrument has autoranging line voltage input. Be sure the supply voltage is within the specified range.

viii

The Agilent 86120B—At a Glance iii

General Safety Considerations vi

1 Getting Started

Step 1. Inspect the Shipment 1-3 Step 2. Check the Fuse 1-5 Step 3. Connect the Line-Power Cable 1-6 Step 4. Connect a Printer 1-7 Step 5. Turn on the Agilent 86120B 1-8 Step 6. Enter Your Elevation 1-10 Step 7. Select Medium for Wavelength Values 1-11 Step 8. Turn Off Wavelength Limiting 1-12 Cleaning Connections for Accurate Measurements 1-13 Returning the Instrument for Service 1-23

2 Using the Multi-Wavelength Meter

Displaying Wavelength and Power 2-3 Changing the Units and Measurement Rate 2-13 Defining Laser-Line Peaks 2-16 Measuring Laser Separation 2-20 Measuring Modulated Lasers 2-23 Measuring Total Power Greater than 10 dBm 2-25 Calibrating Measurements 2-26 Printing Measurement Results 2-28

3 Measurements Applications

Measuring Signal-to-Noise Ratios 3-3 Measuring Signal-to-Noise Ratios with Averaging 3-7 Measuring Laser Drift 3-9 Measuring Coherence Length 3-12

4 Programming

Addressing and Initializing the Instrument 4-3 Making Measurements 4-5 Monitoring the Instrument 4-16 Reviewing SCPI Syntax Rules 4-23 Example Programs 4-28

Contents-1

Contents

Lists of Commands 4-43

5 Programming Commands

Common Commands 5-3 Measurement Instructions 5-15 CALCulate1 Subsystem 5-26 CALCulate2 Subsystem 5-31 CALCulate3 Subsystem 5-43 CONFigure Measurement Instruction 5-64 DISPlay Subsystem 5-64 FETCh Measurement Instruction 5-67 HCOPy Subsystem 5-68 MEASure Measurement Instruction 5-68 READ Measurement Instruction 5-69 SENSe Subsystem 5-69 STATus Subsystem 5-74 SYSTem Subsystem 5-79 TRIGger Subsystem 5-84 UNIT Subsystem 5-86

6 Performance Tests

Test 1. Absolute Wavelength Accuracy 6-3 Test 2. Sensitivity 6-4 Test 3. Polarization Dependence 6-5 Test 4. Optical Input Return Loss 6-6 Test 5. Amplitude Accuracy and Linearity 6-9

7 Specifications and Regulatory Information

Definition of Terms 7-3 Specifications 7-6 Regulatory Information 7-10

8 Reference

Instrument

Preset

Conditions 8-2 Menu Maps 8-4 Error Messages 8-9 Front-Panel Fiber-Optic Adapters 8-15

Contents-2

Power Cords 8-16 Agilent Technologies Service Offices 8-18

Contents

Contents-3

Getting Started

The instructions in this chapter show you how to install your Agilent 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-Wavelength Meter”. Refer to Chapter 7, “Specifications and Regulatory Information” for information on operating conditions such as temperature.

If you should ever need to clean the cabinet, use a damp cloth only.

WARNING

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.

This product is designed for use in INSTALLATION CATEGORY II and POLLUTION DEGREE 2, per IEC 1010 and 664 respectively.

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.

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.

1-2

Getting Started

Step 1. Inspect the Shipment

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 Agilent Technologies sales and service office. Agilent Technologies will arrange for repair or replacement of damaged or incomplete shipments without waiting for a settlement from the transportation company. Notify the Agilent Technologies customer engineer of any problems.

Make sure that the serial number and options listed on the instrument’s rearpanel label match the serial number and options listed on the shipping document. The following figure is an example of the rear-panel serial number label:

1-3

Getting Started

Step 1. Inspect the Shipment

Table 1-1. Options and Accessories Available for the Agilent 86120B

Item Quantity

Option 010 Delete FC/PC connector — —

Option 011 Diamond HMS-10 connector interface 1 08154-61701

Option 013 DIN 47256 connector interface 1 08154-61703

Option 014 ST connector interface 1 08154-61704

Option 017 SC connector interface 1 08154-61708

Option 022 Replace flat physical contact interface with angled physical contact interface

Option 900 Great Britain power cord 1 8120-1703

Option 901 Australia, New Zealand, China power cord 1 8120-0696

Option 902 European power cord 1 8120-1692

Option 906 Switzerland power cord 1 8120-2296

Option 912 Denmark power cord 1 8120-2957

Option 917 India, South Africa power cord 1 8120-4600

Option 918 Japanese power cord 1 8120-4754

——

Agilent Technologies Part Number

Option 919 Israel power cord 1 8120-5181

Option UK5 Protective soft carrying case 1 9211-7314

Option UK6 Commercial calibration certificate with calibration data

Option AXE Rack mount kit with handles 1 86120-60031

Option IX4 Rack mount kit without handles 1 86120-60030

Option OB2 Additional user’s manual 1 86120-90001

Option 412 Add 10 dB external attenuator (FC/PC interface connector)

1-4

1—

1 1005-0587

Step 2. Check the Fuse

Locate the line-input connector on the instrument’s rear panel.

Disconnect the line-power cable if it is connected.

Use a small flat-blade screwdriver to open the pull-out fuse drawer.

Getting Started

WARNING

Verify that the value of the line-voltage fuse in the pull-out drawer is correct. The recommended fuse is an IEC 127 5×20 mm, 6.3A, 250 V, Agilent Technologies part number 2110-0703.

Notice that an extra fuse is provided in a drawer located on the fuse holder.

For continued protection against fire hazard, replace line fuse only with same type and ratings, (type T 6.3A/250V for 100/240V operation). The use of other fuses or materials is prohibited.

1-5

Getting Started

Step 3. Connect the Line-Power Cable

WARNING

CAUTION

This is a Safety Class 1 Product (provided with a protective earthing ground incorporated in the power cord). 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.

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.

connect ac power until you have verified the line voltage is correct as

Do not

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

This instrument has autoranging line voltage input. Be sure the supply voltage is within the specified range.

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

Line Power Requirements

Power: 115 VAC: 110 VA MAX. / 60 WATTS MAX. / 1.1 A MAX.

230 VAC: 150 VA MAX. / 70 WATTS MAX. / 0.6 A MAX.

Voltage nominal: 115 VAC / 230 VAC

range 115 VAC: 90-132 V range 230 VAC: 198-254 V

Frequency nominals: 50 Hz / 60 Hz

range: 47-63 Hz

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

1-6

Getting Started

Step 4. Connect a Printer

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

Various power cables are available to connect the Agilent 86120B to ac power outlets unique to specific geographic areas. The cable appropriate for the area to which the Agilent 86120B is originally shipped is included with the unit. The cable shipped with the instrument also has a right-angle connector so that the Agilent 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

“Front-Panel Fiber-Optic Adapters” on page 8-15.

Step 4. Connect a Printer

The Agilent 86120B can print hardcopies of measurement results on a printer. The output is ASCII text. If you don’t have a printer, continue with “Step 5.

Turn on the Agilent 86120B” on page 1-8.

• Using a standard parallel printer cable, connect the printer to the Agilent 86120B’s rear-panel

PARALLEL PRINTER PORT

connector.

1-7

Getting Started

Step 5. Turn on the Agilent 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.

Press the front-panel should look similar to the following figure:

The front-panel ply after the EMC filters and before other parts of the instrument.

If the Agilent 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 Agilent Technologies for repair. Refer to

“Returning the Instrument for Service” on page 1-23.

LINE

key. After approximately 20 seconds, the display

LINE

switch disconnects the mains circuits from the mains sup-

1-8

Getting Started

Step 5. Turn on the Agilent 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 Agilent 86120B, you may need to indicate this number when communicating with Agilent Technologies.

There is no output laser aperture

Measurement accuracy—it’s up to you!

Before you connect any fiber-optic cable to the Agilent 86120B, refer to “Cleaning Con-

nections for Accurate Measurements” on page 1-13.

1-9

Getting Started

Step 6. Enter Your Elevation

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

Press the

Press

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.

Press

Converting feet to meters

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

Setup

CAL

ELEV

RETURN

key.

softkey.

to complete the entry.

---------------=

3.281

1-10

Getting Started

Step 7. Select Medium for Wavelength Values

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

Press the

Make the following selection:

•Press

Press

Definition of standard air

Standard air is defined to have the following characteristics:

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

Setup

CAL

VACUUM

STD AIR

RETURN

key.

softkey.

for wavelength readings in a vacuum.

for wavelength readings in standard air.

to complete the entry.

1-11

Getting Started

Step 8. Turn Off Wavelength Limiting

After the suring 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:

Press the

Press

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

Preset

Setup

WL LIM

LIM OFF

key is pressed, the input wavelength range is limited to mea-

key.

softkey.

to remove the limits on wavelength range.

1-12

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. Agilent Technologies offers adapters for most instruments to allow testing with many different cables. Figure 1-1 on

page 1-14 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 specifica-

1-13

Getting Started

Cleaning Connections for Accurate Measurements

tions 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. Often 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, Agilent Technologies instruments typically use a connector such as the Diamond HMS-10, which has concentric tolerances within a few tenths of a micron. Agilent Technologies then uses a special universal adapter, which allows other cable types to mate with this precision connector. See Figure 1-2.

1-14

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 0.2µm. This process, plus the keyed axis, allows very precise core-to-core alignments. This connector is found on most Agilent Technologies lightwave instruments.

1-15

Getting Started

Cleaning Connections for Accurate Measurements

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 silver 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-toglass 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 1-20.

1-16

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.

1-17

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

better. The purpose of

not

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.

1-18

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