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LDX-3200
Service Manual
119 pgs1.34 Mb0

ILX Lightwave LDX-3200 Service Manual

User’s Guide
Precision Current Source
LDX-3200 Series
ILX Lightwave Corporation P. O. Box 6310 Bozeman, MT, U.S.A. 59771 : · · · 1-800-459-9459 · ·
www.ilxlightwave.com
U.S. & Canada International Inquiries: 406-586-1244 Fax 406-586-9405
E-mail: support@ilxlightwave.com
7002820200_7/01
Table of Contents
Chapter 1 Introduction to the LDX-3200 Series
Introduction ...............................................................................................................................................................1
Safety Symbols and Terms..............................................................................................................................................2
Product Overview............................................................................................................................................................2
Initial Inspection..............................................................................................................................................................2
Installing your LDX-3200 Precision Current Source.......................................................................................................3
Maintenance ...............................................................................................................................................................4
How to Obtain Repair Services .......................................................................................................................................6
LDX-3200 Series Specifications......................................................................................................................................6
Available Options and Accessories .................................................................................................................................8
Chapter 2 How to Operate Your LDX-3200
Introduction ...............................................................................................................................................................1
Applying Power to Your LDX-3200..............................................................................................................................1
Connecting to the Laser...................................................................................................................................................2
Front Panel Operation.....................................................................................................................................................5
Operating a Laser in Constant Current, “I” Mode.........................................................................................................5
Operating a Laser in Constant Power Mode, P...............................................................................................................7
Error Indicators ...............................................................................................................................................................8
Chapter 3 Operating in Remote Control
Introduction ...............................................................................................................................................................1
LDC-3700B Series Current Source Command Set...........................................................................................................2
Status Reporting..............................................................................................................................................................7
Chapter 4 Command Reference
Introduction ...............................................................................................................................................................1
LDX-3200 Series Device-Dependent Commands...........................................................................................................4
LDX-3200 Series Device-Dependent Command Reference............................................................................................5
Chapter 5 Functions and Features
Introduction ...............................................................................................................................................................1
Saving and Recalling from the Front Panel.......................................................................................................................1
Using the Laser Compliance Voltage Adjustment ...........................................................................................................2
Using the LDX-3200 Trigger Function............................................................................................................................2
Modulating the Laser Current Source..............................................................................................................................3
Chapter 6 Calibration and Troubleshooting Guide
Introduction ...............................................................................................................................................................1
Local Calibration of the LDX-3200 Series Current Source..............................................................................................2
Remote Calibration of the LDX-3200 Series Current Source..........................................................................................6
Troubleshooting Guide..................................................................................................................................................10
CHAPTER 1 1
INTRODUCTION TO THE LDX-3200 SERIES 1
Introduction 1 Product Overview 2 Initial Inspection 2 Installing Your LDX-3200 Precision Current Source 3
Grounding requirements 3 AC Line Power Requirements 3 GPIB Connector 3 The GPIB Address 3 Tilt-Foot Adjustment 4
Operating the LDX-3200 Precision Current Source 4 Maintenance 5 How to Obtain Repair Services 6
General Shipping Instructions 6 LDX-3200 Series Specifications 7
Laser Current Source Specifications 7 Available Options and Accessories 8
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
CHAPTER 1
INTRODUCTION TO THE LDX-3200 SERIES
INTRODUCTION
This chapter is an introduction to the LDX-3200 Series Precision Current Sources containing unpacking information, instructions on how to install and apply power, and safety considerations and instructions. It also contains some maintenance information, specifications, and listings of the LDX-3200 options and accessories.
WARNING
If any of the following symptoms exist, or are even suspected, remove the LDX-3200 from service. Do not use the LDX-3200 until trained service personnel can verify safe operation.
1. Visible damage
2. Severe transport stress
3. Prolonged storage under adverse conditions
4. Failure to perform intended measurements or functions
If necessary, return the LDX-3200 to ILX Lightwave for service and repair to ensure that safety features are maintained.
In order to get the most out of your ILX Lightwave product, we ask that you direct any product operation or service related questions or comments to Customer Support at 1-800-459-9459 (USA and Canada), 406-586-1244 (International) or by fax at 406-586-9405. Or E-mail us at SUPPORT@ILXLIGHTWAVE.COM.
When calling, please have the following information on hand (if applicable):
1) Product Model: ________________________________________________
2) Unit Serial Number: ________________________________________________
3) End user name and telephone/fax Name: ________________________________________________ Company: ________________________________________________ Phone: ________________________________________________ Fax: ________________________________________________
4) Description/sketch of what is connected to the ILX Lightwave instrument.
5) Description of the problem.
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
PAGE 1
SAFETY SYMBOLS AND TERMS
The following safety terms are used in this manual:
• The WARNING heading explains dangers that could result in personal injury or death.
• The CAUTION heading explains hazards that could damage your instrument.
• The NOTES heading gives information to the user that may be beneficial in the use of the instrument and to the
devices being tested.
The following symbols are used in this manual and on the instrument:
Earth Ground and/or Protective conductor terminal
Caution: Refer to accompanying documents
Caution: Risk of Electrical Shock
Instrument Power Off
Instrument Power On
PRODUCT OVERVIEW
The LDX-3200 Series instruments are precision current sources. They provide a high stability output with a fully redundant current limit and multiple laser protection features. The LDX-3200 Series' fast, sophisticated GPIB option lets you automate your experiment.
INITIAL INSPECTION
When you receive your LDX-3200 instrument, verify that the following items were shipped with the instrument:
LDX-3200 Series Precision Current Source LDX-3200 Series Instruction Manual Power Cord Shipping Kit
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
PAGE 2
INSTALLING YOUR LDX-3200 PRECISION CURRENT SOURCE
Grounding requirements
The LDX-3200 Series Precision Current Source comes with a three conductor AC power cable. The power cable must either be plugged into an approved three-contact electrical outlet or used with a three-contact or two-contact adapter with the grounding wire connected to an electrical ground (safety ground). The LDX-3200’s power jack and supplied power cable meet IEC safety standards.
AC Line Power Requirements
You can operate the LDX-3200 Series instrument from a single phase power source delivering nominal line voltages of 100, 120, 220, or 240 VAC (all values RMS), at 50/60 Hz. The line power voltage can vary + 10% but cannot exceed 250 VAC. Maximum power consumption is 60 VA (Volt-Amps). The instrument’s operational voltage is factory configurable and need not be changed before operating the instrument. However, check to be sure that the voltage printed on the back panel of the instrument matches the power-line voltage in your area.
WARNING
Before connecting the LDX-3200 Series Precision Current Source to a power source, verify that the AC power source matches the setting of the LDX-3200’s voltage printed on the rear panel of the instrument.
To avoid electrical shock hazard, connect the instrument to properly earth-grounded, 3-prong receptacles only. Failure to observe this precaution can result in severe injury or death.
GPIB Connector
The IEEE 488.2 GPIB interface connector is located on the rear panel, directly above the power input module and fuse. See Figure 1.2, LDX-3200 Series Rear View. Attach the GPIB cable to the 24-pin connector located on the rear panel. The connector is tapered to ensure proper orientation. Using your fingers, tighten the two screws on the cable connector.
A total of 15 devices can be connected together on the same GPIB interface bus. The cables have single male/female connectors on each end so that several cables can be stacked. This allows more than one cable to be attached to any one device. However, the maximum length of the GPIB cables must not exceed 20 meters (65 feet) total, or 2 meters (6.5 feet) per device.
The GPIB Address
The talk and listen addresses on the LDX-3200 Series Precision Current Source are identical. This GPIB address is read locally by pressing the (GPIB) LOCAL switch with the address displayed on the LCD display. The instrument comes from the factory configured with the GPIB address set to 1. You can change the LDX-3200’s GPIB address locally (via front panel). A procedure for changing the address can be found in the section “Changing the GPIB Address” in Chapter 3.
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
PAGE 3
Tilt-Foot Adjustment
The LDX-3200 Series Precision Current Source comes standard with folding front legs and two rear feet for use as a bench top instrument. Extending the front feet so that the instrument front panel sits up makes it easier to view the LED displays. To use them, place the unit on a stable base and rotate the front legs downward until they lock into position.
Operating the LDX-3200 Precision Current Source
Now that the LDX-3200 Precision Current Source is installed and ready for use, you can begin to learn about its operation. The following figures are photographic copies showing the functional keypad groupings, back panel connectors, and so on. Use these figures to familiarize yourself with the LDX-3200. After that, use Chapter 2 for fundamentals of operating your instrument.
Power Switch
Parameter Selection
Display
Laser Mode Selection
Adjust Section
Current Range Selection
Modulation Input Connector
FIGURE 1.1 LDX 3200 Series Front View
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
PAGE 4
PD Bias Adjust
LD Connector
GPIB Connector
Trigger Output Connector
FIGURE 1.2 LDX-3200 Series Rear View
Power Cord Connector
MAINTENANCE
This section covers information on how to obtain repair services.
WARNING
Potentially lethal voltages exist within the LDX-3200 Series Precision Current Source. To avoid electric shock, do not perform any of the maintenance on the instrument unless you are qualified to do so. Qualified service personnel are required to wear protective eyeglasses and anti-static wristbands while working on the LDX-3200 Series Precision Current Source circuit boards. High voltages are present on and around the instrument’s printed circuit boards.
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
PAGE 5
HOW TO OBTAIN REPAIR SERVICES
You may have to return your instrument to the ILX Lightwave facility at some time for repair or service whether it is under warranty or not. There is a charge for repairs after the warranty period has expired. Contact an ILX Lightwave service representative for shipping instructions prior to returning the instrument. Have the model number, instrument serial number and a description of the problem or request at the time of the call. All ILX Lightwave instruments are identified by a serial number located on the rear panel. The first four or five digits are the model number, the last four digits are unique to the instrument and identify your instrument specifically. A return authorization number will be given to you at the time of your request for repair or service. Please use this number in all communications concerning your instrument.
General Shipping Instructions
If you need to ship your LDX-3200 Precision Current Source back to the factory for repair, be sure that the LDX-3200 is packaged in an enclosure with cushioning material to prevent damage to the instrument during shipment (use the original shipping containers and accessories if possible). Re-install the ESD protective caps on the rear and front panels over the connectors (9 pin D, BNC, and GPIB). Shipping damage is not covered under warranty.
Attach a tag to the instrument identifying the owner and indicating the service or repair needed. Include the model number and serial number. We suggest that you insure the shipment.
In North America, contact ILX Lightwave for return authorization and shipping instructions. Outside of North America, contact your ILX distributor for the shipping information.
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
PAGE 6
LDX-3200 SERIES SPECIFICATIONS
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±2 µA±2 µA±2 µA±2 µ
Laser Current Source Specifications
Model Number LDX-3210 LDX-3220
DRIVE CURRENT OUTPUT Output Current Range: 0 to 50 mA 0 to 100 mA 0 to 200 mA 0 to 500 mA Set-Point Resolution: 1 µA 2 µA 4 µA 10 µA Set-Point Accuracy (% of FS): Compliance Voltage: 0 - 10 V, 0 - 10 V, 0 - 10 V, 0 - 10 V,
Temperature Coefficient: <50 ppm/°C <50 ppm/°C <50 ppm/°C <50 ppm/°C Short-Term Stability (1 hr.): Long-Term Stability (24 hr.): Noise and Ripple (µA rms) High Bandwidth Mode: <1.5 µA <1.5 µA <4 µA <4 µA Low Bandwidth Mode: <1.5 µA <1.5 µA <2 µA <2 µA Transients Operational: 1kV EFT/Surge:
COMPLIANCE VOLTAGE ADJUST Range: 0 - 10 V 0 - 10 V 0 - 10 V 0 - 10 V Resolution: 50 mV 50 mV 50 mV 50 mV Accuracy:
DRIVE CURRENT LIMIT SETTINGS Range: 1 to 50.5 mA 1 to 101 mA 1 to 202 mA 1 to 505 mA Resolution: 0.25 mA 0.5 mA 1 mA 2.5 mA Accuracy:
PHOTODIODE FEEDBACK Type: Differential Differential Differential Differential PD Reverse Bias : 0 - 5V, adjustable 0 - 5V, adjustable 0 - 5V, adjustable 0 - 5V, adjustable PD Current Range : 5 to 5000 µA 5 to 5000 µA 5 to 5000 µA 5 to 5000 µA Output Stability: Accuracy, set point (% of FS):
EXTERNAL ANALOG MODULATION Input: 0-10V, 10k Ω 0-10V, 10kΩ 0-10V, 10kΩ 0-10V, 10kΩ Transfer Function: 5 mA/V 10 mA/V 20 mA/V 50 mA/V Bandwidth (3 dB) High Bandwidth: Low Bandwidth:
TRIGGER OUTPUT Type: TTL TTL TTL TTL Pulse Width: 13 µS 13 µS 13 µS 13 µS Delay: 12 mS 12 mS 12 mS 12 mS
MEASUREMENT (DISPLAY) Output Current Range: 0 to 50.000 mA 0 to 100.00 mA 0 to 200.00 mA 0 to 500.00 mA Output Current Resolution: 0.001 mA 0.002 mA 0.01 mA 0.01 mA Output Current Accuracy:
Photodiode Current Range: 0 to 5,000 µA 0 to 5,000 µA 0 to 5,000 µA 0 to 5,000 µA Photodiode Current Resolution: 1 µA 1 µA 1 µA 1 µA Photodiode Current Accuracy: PD Responsivity Range: PD Responsivity Resolution: 0.01 µA/mW 0.01 µA/mW 0.01 µA/mW 0.01 µA/mW Optical Power Range: 0.00 to 101.00 mW 0.00 to 101.00 mW 0.00 to 505.00 mW 0.00 to 505.00 mW Optical Power Resolution: 0.01 mW 0.01 mW 0.01 mW 0.01 mW
Forward Voltage Range: 0.000 to 10.000 V 0.000 to 10.000 V 0.000 to 10.000 V 0.000 to 10.000 V Forward Voltage Resolution: 1 mV 1 mV 1 mV 1 mV Forward Voltage Accuracy:
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1
0.05%
0.05%
0.05%
0.05%
adjustable adjustable adjustable adjustable
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<10 ppm <10 ppm <10 ppm <10 ppm <20 ppm <20 ppm <20 ppm <20 ppm
<1 mA <1 mA <1 mA <1 mA <5 mA/< 8 mA <5 mA/< 8 mA <8 mA/< 12 mA <8 mA/< 12 mA
2.5%
0.5 mA
0.02%
0.05%
DC to 1 MHz DC to 1 MHz DC to 1 MHz DC to 1 MHz DC to 15 kHz DC to 15 kHz DC to 15 kHz DC to 15 kHz
0.05% FS
0.00 to 1000.00 µA/mW 0.00 to 1000.00 µA/mW 0.00 to 1000.00 µA/mW 0.00 to 1000.00 µA/mW
2.5%
1 mA
0.02%
0.05%
0.05% FS
2.5%
2 mA
0.02%
0.05%
0.05% FS
2.5%
5 mA
0.02%
0.05%
0.05% FS
A
±2 mV ±2 mV ±2 mV ±2 mV
1 All values relate to a one-hour warm-up period. 2 Over any 1-hour period, half-scale output. 3 Over any 24-hour period, half-scale output. 4 Measured optically, evaluating noise intensity of a laser diode into a photodectector with 150 kHz bandwidth. Request ILX Application Note #3. 5 Maximum output current transient resulting from normal operational situations (e.g., power on-off, current on-off), as well as accidental situations (e.g., power line plug
6 Maximum output current transient resulting from a 1000 V power-line transient spike. Tested to ILX Lightwave Technical Standard #LDX-00196. Request ILX Application Note
7 Maximum monitor photodiode current drift over any 30 minute period. Assumes zero drift in responsivity of photodiode. 8 300 mA set point, 60 mA modulation current. 9 Small signal specification is for typ. 10% modulation depth. Large signal spec. assumes 50% modulation depth at mid-scale output. 10 Responsivity value is user-defined and is used to calculate the optical power. 11 Four wire voltage measurement at the load. Voltage measurement accuracy while driving calibration load. Accuracy is dependent upon load and cable used.
removal).
#3.
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
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GENERAL
Size (H x W x D) 4" x 8.5" x 13.4", 102 mm x 216 mm x 340 mm Weight LDX-3210 approx 12 lbs (5.5 kg) LDX-3220 approx 12 lbs (5.5 kg) Power (50-60 Hz) 100 V, ±10%
Temperature 0 to +40 °C operating; -40 to +70 °C storage Humidity < 90 % relative humidity, non-condensing. Laser Safety Features: Key switch, interlock and output delay (meets CDRH US21 1040.10) Display type: 5-digit, green LED
120 V, ±10% 220 V, ±10% 230-240 V, ±10%
AVAILABLE OPTIONS AND ACCESSORIES
Options and accessories available for the LDX-3200 Series Precision Current Sources include the following:
DESCRIPTION MODEL NUMBER
Rack mount flange kit Tba
Temperature Controlled Laser Diode Mount LDM-4407 Temperature Controlled Laser Diode Mount (available with collimating assembly) DIL Laser Diode Mount LDM-4982 Butterfly Laser Diode Mount LDM-4894 High Power Laser Diode Mount LDM-4442 Current Source Interconnect Cable (unterminated) CC-306S Current Source Interconnect Cable (terminated) CC-305S
LDM-4412
Other Laser Diode Mounts are available. Please contact ILX Lightwave for information on additional options for your applications.
INTRODUCTION TO THE LDX-3200 SERIES CHPT 1
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CHAPTER 2 1
HOW TO OPERATE YOUR LDX-3200 1
INTRODUCTION 1 APPLYING POWER TO YOUR LDX-3200 1
The Power-On Sequence 1 The Power-On State 1
CONNECTING TO THE LASER 2
Interlock Connections 4 Photodiode Connections 4 Setting the PD bias 4 Grounding considerations 4
FRONT PANEL OPERATION 5
The Display 5
OPERATING A LASER IN CONSTANT CURRENT, “I” MODE 5
Setting Up the Precision Current Source 5 Conditions Which Will Automatically Shut Off the LASER OUTPUT 6
OPERATING A LASER IN CONSTANT POWER MODE, P 7
Entering Photodiode Responsivity values 7
ERROR INDICATORS 8
HOW TO OPERATE YOUR LDX-3200 CHPT 2
Chapter 2
HOW TO OPERATE YOUR LDX-3200
INTRODUCTION
This chapter introduces you to the operation of the LDX-3200 Series Precision Current Source. It offers instructions for connecting your laser to the current source, and describes powering up the instrument. This chapter also contains step by step procedures that teach you how to operate your current source in Constant Current Mode and Constant Power Mode. We recommend that you review the contents of this chapter at a minimum before operating the LDX-3200 Series Precision Current Source.
APPLYING POWER TO YOUR LDX-3200
To turn on the LDX-3200, rotate the key in the “POWER” section of the front panel from “O” to “I”. This action will initiate the power on sequence. If the LDX-3200 does not appear to turn on, verify that it is connected to line power. If line power is not the problem, remove the power cord and check the line power fuse.
The Power-On Sequence
During the power-up sequence, the following takes place. For about three seconds all indicators light up, and all of the 7-segment displays indicate "8". Then all lamps are turned off for three seconds. Next, the firmware version will be displayed. Then, a self-test is performed to ensure that the instrument’s hardware and processor are communicating. After this test, the instrument is ready to operate, and is configured to the state it was in when the power was last shut off.
The Power-On State
You can choose to "clear" the last saved state by recalling the default values. These values are stored in BINS to which you can save or recall instrument configurations (described in more detail in Chapter 5). "BIN 0" contains all of the default configurations listed in Table 2.1.
NOTE
If the instrument cannot successfully complete the power on test, an error message of E-512 or E-513 will be displayed on the Display. See Chapter 3 for a list of error codes and actions to take when your instrument indicates these errors.
HOW TO OPERATE YOUR LDX-3200 CHPT 2
PAGE 1
LDX-3200 Series DEFAULT CONFIGURATION
GPIB mode in LOCAL via front panel, or in REMOTE via GPIB PARAMETERS not selected CAL PD = 0 µA/mW LIM I (high range) = 125 mA (LDX-3220), 25 mA (LDX-3210) LIM I (low range) = 50 mA (LDX-3220), 12.5 mA (LDX-3210) LIM V = 10 volts LIM P = 1000 mW (LDX-3220), 200 mW (LDX-3210) LASER output off LASER DISPLAY enabled, in I mode Constant I, low bandwidth mode selected LASER display showing actual current (0.00 with output off) LASER STEP value = 1 (see LAS:STEP command, chapter 4) LASER Tolerance values = 1.00 mA, 1.0 seconds LASER I Set Point = 0 mA LASER IPD Set Point = 0 µA LASER PPD Set Point = 0 mW RECALL BIN number = 0 MODULATION Enabled
Table 2.1 LDX-3200 Series Default Settings
CONNECTING TO THE LASER
When connecting your laser or any other sensitive devices to the LDX-3200 Series Precision Current Source, we recommend that the instrument be powered up and the LASER output be off (MODE) ON LED unlit. In this condition, a low impedance shunt is active across the output terminals. When disconnecting devices, it is only necessary to turn the current source output off.
It is also recommended that the connections to the LDX-3200 Series Precision Current Source output be made using twisted wire pairs with an earth-grounded shield (see Figures 2.1 A - D). The output terminals of the instrument are left floating relative to earth ground to suppress AC power-on/power-off transients that may occur through an earth­ground path. If the output circuit is earth-grounded at some point (such as through the laser package and mount), the user must be careful to avoid multiple earth grounds in the circuit. Multiple earth grounds may provide circuit paths that induce spurious currents in the photodiode feedback circuit and output leads.
IMPORTANT
Experience indicates that should an open circuit occur during laser operation (while the LASER is ON), the laser may be damaged by a momentary circuit break-and-remake before the final circuit break. The cable connections to the laser must be secure enough that they will not open-circuit, should they be jostled or bumped.
Figures 2.1A - D show the possible configurations of connecting laser diodes and photodiodes with the LDX-3200 Series Precision Current Source.
HOW TO OPERATE YOUR LDX-3200 CHPT 2
PAGE 2
+
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LDX-3200 Series Precision Current Source
OUTPUT
+
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LDX-3200 Series Precision Current Source
+
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LDX-3200 Series Precision Current Source
+
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LDX-3200 Series Precision Current Source
7
Bias
+
6
9
5
P. D. L. D.
3
Earth Ground
Figure 2.1A Common Laser Cathode - Photodiode Cathode
OUTPUT
7
Bias
+
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5
P. D. L. D.
3
Earth Ground
Figure 2.1B Common Laser Cathode - Photodiode Anode
OUTPUT
7
Bias
+
6
9
5
P. D. L. D.
3
Earth Ground
Figure 2.1C Common Laser Anode - Photodiode Cathode
OUTPUT
7
Bias
+
6
9
5
P. D. L. D.
3
Earth Ground
Figure 2.1D Common Laser Anode - Photodiode Anode
HOW TO OPERATE YOUR LDX-3200 CHPT 2
PAGE 3
The 9-pin connector marked CURRENT SOURCE on the back panel is used to connect your laser diode to the
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LDX-3200. There are connections provided for laser cathode and anode, photodiode cathode and anode, chassis ground and interlock. The pinout diagram for this connector is shown in Figure 2.2.
1, 2 Interlock
3 Chassis Ground
4 Cathode Voltage Sense
5 Laser Cathode 6 PD Cathode (+) 7 PD Anode (-) 8 Anode Voltage Sense 9 Laser Anode
1 2
7
3
8
4
9
5
Figure 2.2 Back Panel LD Connector
Interlock Connections
In order for the laser output to be enabled a short circuit must exist between the Interlock pins (pins 1 and 2) of the connector. The short can be a direct short across the pins or a switch to prevent laser operation until the switch is closed. If a short does not exist between these two pins, the INTERLOCK LED will illuminate on the front panel and the laser output will be disabled.
CAUTION
The interlock terminals on the LASER connector, pins 1 and 2, must be kept isolated from all other connections including earth ground.
Photodiode Connections
Many laser diode modules contain an internal photodiode that monitors the back-facet emission of the laser. Usually, this photodiode is internally connected to either the laser anode or cathode.
The photodiode and laser connections to the LDX-3200 Series Precision Current Source are electrically isolated from ground and each other. So, if a 4-pin connection is made (no common connections) no additional jumpers are required. Figures 2.1A - 2.1D show the recommended connections and shielding for 3-pin lasers (where the common connection is internal to the device). A 4-pin laser should be connected with the same shielding as shown in Figure
2.1, but the common connection (between the photodiode and the laser) is optional.
Setting the PD bias
The LDX-3200 Series Precision Current Source provides an adjustable reverse bias of 0 - 5 VDC for the photodiode. To set the photodiode bias to 5 volts reverse bias, turn the back panel PHOTODIODE BIAS ADJUST fully clockwise. To set the photodiode bias to 0 volts reverse bias, turn the back panel PHOTODIODE BIAS ADJUST fully counter­clockwise
Grounding considerations
The LASER outputs of the LDX-3200 Series Precision Current Source are isolated from chassis ground allowing either output terminal to be grounded at the user's option. Figure 2.1 shows the proper earth-ground shielding for laser diode/photodiode connections.
HOW TO OPERATE YOUR LDX-3200 CHPT 2
PAGE 4
FRONT PANEL OPERATION
This section describes fundamentals of operation for your LDX-3200 Series Precision Current Source in two operating modes, Constant Current (I), and Constant Power (P).
The Display
The digital display is used to show control parameters such as laser drive current (mA), laser current limit (mA), laser forward voltage (V), voltage limit (V), monitor photodiode current (µA), and laser optical power (mW) in both set point and measurement modes. It will also
display error codes that relate to LASER operation. Error indicators underneath the display indicate control errors and are explained in the section titled “ERROR INDICATORS”. All laser control parameters are displayed on this digital display with the appropriate annunciator illuminated.
OPERATING A LASER IN CONSTANT CURRENT, “I” MODE
Suppose you have an LDX-3220 and you want to run the instrument in Constant Current, low bandwidth mode, with a set point of 150 mA and a current limit of 175 mA. This particular mode uses a low-pass filter on the laser drive current output to significantly reduce noise. In this mode a modulation input of up to 15 kHz may be used, via the front panel MOD EXTERNAL connector. Follow the instructions below in the sequence presented.
Setting Up the Precision Current Source
Set the LDX-3200 in Constant Current, low bandwidth mode by selecting I in the MODE section of the front panel. Do this by toggling the SELECT push button until the I indicator is illuminated. Repeatedly pressing the (MODE) SELECT switch cycles through the current (I), light power (P), or high-bandwidth current (I
Next, in the RANGE section set the current source range by selecting the 200 mA range indicated by the accompanying LED. You will need to press the SELECT push button twice to change the range. It must be pressed twice quickly (within less than 1 second) to switch between ranges, and the LASER output must be off (LASER MODE ON indicator unlit) in order to change ranges.
Configure the display so that it reads laser current in mA. Press and release the SELECT switch in the DISPLAY section of the front panel until the mA annunciator is lit. The (DISPLAY) SELECT switch is also used to select the
I
(photodiode current, µA), PPD (laser power, mW), or V (forward voltage, V) measurement or set point display
PD
modes. When the set point mode is active, the corresponding annunciator will flash to indicate set point rather than measurement display.
) control modes.
HBW
To just view the set point, press and hold down the display SELECT switch for two or more seconds. When the SELECT switch is released the previous measurement mode will be restored.
HOW TO OPERATE YOUR LDX-3200 CHPT 2
PAGE 5
At this point the LDX-3200 Series current source is in Constant Current Mode, (I), in the 200 mA range, and the display is reading in mA. Next, we need to adjust the set point of the laser current source.
To adjust the set point of the current source to 150 mA, turn the adjust knob to vary the set point. When the adjust knob is turned, the LDX-3200 automatically changes to set point mode indicated by the flashing annunciator. Adjust the set point to 150 mA. After an adjustment has been made, and the adjust knob is released, the set point mode will time out in three seconds. The display will revert to the original measurement display mode (I, IPD, V, or PPD).
We’re not quite ready to turn on the laser. One of the laser protection features our precision current sources offer is a fully independent hardware current limit. The current limit protects your laser by never allowing the laser drive current to exceed the limit independent of the set point and the output control mode (Constant Current or Constant Power).
To set the current source limit, use the SELECT push button in the PARAMETER section of the front panel to select LIM I . Press and hold the (PARAMETER) SET push button and rotate the adjust knob to vary the limit set point value. Set the limit to 175 mA. Once the (PARAMETER) SET push button is released, the new parameter value is stored in non-volatile memory.
When the LASER current limit is reached, the CURRENT LIMIT error indicator flashes. The current limit setting is independent of the voltage drop of the device connected to the LASER output, and therefore, no dummy load is required for precise adjustment of the current limit. Furthermore, since the current limit circuitry is fully independent of the main current control, the current limit can be adjusted safely, even while the LASER output is active.
An additional feature of the LDX-3200 Series instruments is an adjustable voltage limit. This allows an extra level of laser protection in the event of an intermittent open circuit. For maximum protection via the fastest open-circuit detection, the voltage limit should be set to a value slightly greater than the intended operating voltage.
To set the LASER voltage limit, use the SELECT push button in the PARAMETER section of the front panel to select COMP V and then press and hold the (PARAMETER) SET push button. While holding the (PARAMETER) SET push button, adjust the voltage limit using the adjust knob.
Now you are ready to enable the current source output for your laser diode.
In the MODE section of the front panel, press the push button labeled OUTPUT. The accompanying LED labeled ON will illuminate, indicating that the laser current source’s output is enabled. The instrument will drive the current source to the value set by the corresponding MODE set point. When the LASER output is off, an internal short is placed across the LASER output. The OUTPUT switch has a toggling action. Pressing the switch again will disable the current source output and the ON LED will not be illuminated. The
default condition for the current source output is off when the instrument is first powered up. With the laser output enabled, the LASER display should be indicating measured laser current. If the output won’t function, check the following conditions:
Conditions Which Will Automatically Shut Off the LASER OUTPUT
The following conditions will automatically cause the instrument to disable the current source output:
1. LASER High Power Limit
2. LASER Interlock/Key Lock turned off
3. LASER Open Circuit or Voltage Limit
HOW TO OPERATE YOUR LDX-3200 CHPT 2
PAGE 6
OPERATING A LASER IN CONSTANT POWER MODE, P
Suppose you want to operate a 3 mW laser at constant 1 mW level. The LDX-3200 Series instrument allows you to operate the laser current source driver in a Constant Power mode. In this mode, the LDX-3200 Series instrument drives current to the laser to reach a set point power value (in mW). The control loop feedback parameter is photodiode current that the LDX-3200 converts to optical power via a user-defined photodiode responsivity number. If laser power changes due to internal or environmental conditions, the LDX-3200 will increase/decrease the current to the laser to maintain the power set point. The following paragraphs detail the instrument configuration in Constant Power Mode.
To set the LDX-3200 in Constant Power mode, select P in the MODE section of the front panel by toggling the SELECT push button. Repeatedly pressing the (MODE) SELECT switch cycles through the current (I), light power (P), or high bandwidth current (I
HBW
) control
modes. The LED indicator shows the selected mode.
Entering Photodiode Responsivity values
The photodiode responsivity, CAL PD, is used to convert between photodiode current and optical power of the laser diode. To enter the CAL PD parameter, select
CAL PD with the (PARAMETER) SELECT push button by toggling down past LIM P. The indicator becomes lit when CAL PD is selected and the display indicates the
responsivity parameter in µA/mW (not enunciated). Rotate the adjust knob while holding the (PARAMETER) SET push button to enter a new value for responsivity. When the correct value is displayed, store the number by releasing the (PARAMETER) SET pushbutton.
A method to calculate the responsivity is suggested below.
1. Measure (with a calibrated detector) the output power of the device.
2. Measure the corresponding photodiode current.
3. Calculate the responsivity by dividing the photodiode current by the optical power noting the units
required are µA/mW.
The LDX-3200 Series Precision Current Source can be put into a special mode with the CAL PD parameter set to zero. When the CAL PD value is zero, the LASER output will be controlled to the IPD set point value. Therefore, the instrument is in Constant IPD mode. The display will indicate "-.-" for the power measurement.
Next, configure the display so that it reads in mW by pressing and releasing the (DISPLAY) SELECT switch until the mW annunciator is lit.
Adjust the Constant Power set point of the LDX-3200 to 1.00 mW. To do this, turn the adjust knob to vary the set point. When the adjust knob is turned, the LDX-3200 automatically changes to set point mode as indicated by the flashing annunciator. Adjust the set point to 1.00 mW. After an adjustment has been made, and the adjust knob is released, the set point mode will time out in three seconds. The display will then return to the measurement display mode (I, IPD, V, or PPD).
Before the laser output is enabled, the power limit for the laser under test should be set. In Constant Power mode, this is accomplished by setting a Power limit, LIM P value. The LDX-3200 uses the responsivity value entered to calculate a power limit as a function of monitor current (Ipd). This is a software limit only.
HOW TO OPERATE YOUR LDX-3200 CHPT 2
PAGE 7
To set the Constant Power limit, use the SELECT push button in the PARAMETER section to select LIM P. When the LIM P is indicated by the accompanying LED, the display will indicate the limit set point in mW. Press and hold the (PARAMETER) SET push button and rotate the adjust knob to set the limit to 1.50 mW. When the desired value is reached, release the (PARAMETER) SET push button to store the new limit value.
The LIM P is the absolute limit of optical power, as detected by the unit via the monitor PD feedback loop. In order for this limit to be meaningful, the monitor photodiode responsivity (CAL PD) must be adjusted correctly. This limit is a software limit only. The LASER output is normally turned off if this limit is reached (See LASer:ENABle:OUTOFF command in Chapter 4 for instructions on disabling this function). The maximum LIM P value is 100.0 mW (LDX-
3210), and 500.0 mW (LDX-3220).
Also, in constant power mode the LASER current limit and voltage limit values are in effect. Refer to the discussion on page 8 that describes how to set these limits.
Now the instrument is configured to operate in Constant Power Mode. In the MODE section, enable the output of the laser current source by depressing the OUTPUT push button once. The accompanying led labeled ON will illuminate indicating that the laser output is on and current is being driven to the laser. The LDX-3200 current source will drive the laser to the Constant Power set point and maintain closed loop control with the PD current measurement.
ERROR INDICATORS
The LDX-3200 Series Precision Current Sources indicate general operational error conditions. Each error condition results in an action as shown in the following table.
ERROR INDICATORS
Error Condition Action
Interlock Output off, INTERLOCK light flashes at 1 Hz Open circuit Output off, OPEN CIRCUIT light flashes at 1 Hz.
If this condition was caused by an excessively high compliance voltage, the VOLTAGE LIMIT light will also be turned on.
Current limit CURRENT LIMIT light flashes at 1 Hz Voltage limit VOLTAGE LIMIT light flashes at 1 Hz. This indicator warns that the
output is within 0.25 volts of LIM V setting. If the voltage limit (LIM V) is reached, the LASER output will shut off.
Optical Output Power Limit Output off, POWER LIMIT light flashes at 1 Hz
Table 2.2 LDX-3200 Error Indicators
HOW TO OPERATE YOUR LDX-3200 CHPT 2
PAGE 8
CHAPTER 3 1
OPERATING IN REMOTE CONTROL 1
INTRODUCTION 1
Reading the GPIB Address 1 Changing the GPIB Address 1 Changing Operation from Local to Remote 1
LDX-3200 SERIES CURRENT SOURCE COMMAND SET 2
Command Syntax 2 Command Paths 4 IEEE488.2 Common Commands 5 LDX-3200 Current Source Often Used Commands 6
STATUS REPORTING 7
Event and Condition Registers 7 Operation Complete Definition 7 Output Off Register 9 Command Timing and Completion 10 Error Messages 11
OPERATING IN REMOTE CONTROL CHPT 3
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