Lightwave Communications LDX-3232 manual Method to calculate the responsivity is suggested below

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C H A P T E R 2

O P E R A T I O N

Operating a Laser in Constant Power (P) Mode

A method to calculate the responsivity is suggested below.

1Measure (with a calibrated detector) the output power of the device.

2Measure the corresponding photodiode current.

3Calculate the responsivity by dividing the photodiode current by the optical power noting the units required are µA/mW.

The LDX-3232 High Compliance 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 setpoint 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 setpoint of the LDX-3232 to 1.00 mW. To do this, turn the adjust knob to vary the setpoint. When the adjust knob is turned, the LDX-3232 automatically changes to setpoint mode as indicated by the flashing annunciator. Adjust the setpoint to 1.00 mW. After an adjustment has been made, and the adjust knob is released, the setpoint 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-3232 uses the responsivity value entered to calculate a power limit as a function of monitor current (IPD). This is a software limit only.

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 setpoint 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 photodiode 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 5000.0 mW.

Also, in constant power mode the LASER current limit and voltage limit values are in effect. Setting of these limits is described later in this chapter.

18 LDX-3232

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Contents User’s Guide Page Table of Contents Remote Operation Command Reference Iv LDX-3232 List of Figures Vi LDX-3232 List of Tables Viii LDX-3232 Safety Information and the Manual General Safety ConsiderationsSafety Symbols Safety Marking SymbolsWarranty Claims for Shipping Damage Description of the problem Comments, Suggestions, and ProblemsModel Number Serial Number End-User Name Company Phone Fax Xiv LDX-3232 Introduction and Specifications Product OverviewInitial Inspection Installing Your LDX-3232 High Compliance Current SourceAC Line Power Requirements Grounding RequirementsGpib Address Gpib ConnectorTilt-Foot Adjustment Operating the LDX-3232 Precision Current SourceLDX-3232 Front View Maintenance Specifications TTL Type Pulse Width Delay13 µs 12 ms Available Options and Accessories Description Model NumberApplying Power to Your LDX-3232 Power On SequenceConnecting to the Laser Power On StateCommon Laser Cathode Photodiode Anode Back Panel LD Connector Interlock ConnectionsPhotodiode Connections Setting the PD BiasGrounding Considerations Front Panel Operation Operating a Laser in Constant Current I ModeDisplay Setting Up the Precision Current Source E R a T I O N Operating a Laser in Constant Power P Mode Entering Photodiode Responsivity ValuesMethod to calculate the responsivity is suggested below Error Indicators LDX-3232 Error IndicatorsError Indicators LDX-3232 Reading the Gpib Address Changing the Gpib AddressCommand Syntax LDX-3232 Current Source Command SetChanging Operation from Local to Remote OFF OLD NEW True False SET Reset LASLDI? Command Paths LDX-3232 Command Path StructureIEEE488.2 Command Commands None LDX-3232 Frequently Used CommandsLIM Event and Condition Registers Status ReportingOperation Complete Definition LDX-3232 Status Reporting Schematic Diagram Disabled 10 N/A Enabled 11 N/A 12 N/A 13 N/A 14 N/A 15 N/A Output Off RegisterLASerENABleOUTOFF nrf LASerENABleOUTOFF? Command Timing and Completion Error MessagesError Code Classifications Response MessageMode Used to enter the laser current calibration mode Used to create a delay in the execution of furtherCommands Used to enter the laser voltage calibration modeSets the enable register for Laser conditions Returns status of photodiode monitor power displayEnables Laser display to show parameter values Returns the value of the LAS conditions enable registerUsed to enable/disable the front panel modulation input Used to return the optical power from monitorUsed to set the constant optical power setpoint, if Or P optical powerReturns the elapsed time since the timer was last reset Returns the status of the Term commandPowered up Used to return the Laser setpoint tolerance valueLDX-3232 Device-Dependent Commands Command Description FormatLDX-3232 Device-Dependent Command Reference DelayLASerCALMD ERRors?Calmd LAS Calpd Responsivity CAL PD parameter setting Syntax Diagram LASerCALMD?LASerCALLDI Selected. This procedure is outlined in ChapterCalibration for that bandwidth LDI LAS CAL LASerCALLDI?LASerCALLDV LAS CAL LDVLASerCALLDV? True measured value. This procedure is outlined in ChapterLASerCALMDI MDI LASerCALMDI?LASerCOND? LAS CAL IPDLASerDEC LAS DIS LASerDISplayLASerDISplay? LASDIS?Lasdisldi LASerDISplayLDILASerDISplayLDI? LDILASerDISplayLDV? Voltage measurement Syntax DiagramLASerDISplayLDV LASDISLDV?LAS DIS MDI LASerDISplayMDILASerDISplayMDI? LAS DIS IPDPPD LASerDISplayMDPLASerDISplayMDP? LAS DIS MDPLAS DIS Param LASerDISplayPARAMLASerDISplaySET LAS DIS SETLASerDISplaySET? LASerENABleCONDLASDISPLAYSET? Bit LASerENABleCOND?LAS Enab Cond Action enables the Laser status event register so that LASerENABleEVEntAn nrf value whose sum represents the bits that are enabled LasenabeventLASerENABleEVEnt? LAS Enab EVELASerENABleOUTOFF LASerENABleOUTOFF? LAS Enab OutoffLASerEVEnt? LASerENABleEVEnt commandCommand while the condition status is constantly changing LAS EVELASerINC Function for the Laser outputLASerLDI? This measurement is updated approximately once every 600 msLASerLDI LAS LDIFor LDV calibration LASerLDVLASerLDV? LAS LDVLimit in use depends on the Laser output range selection LASerLIMitI2LASerLIMitI2? LAS LIMLASerLIMitI4? Displayed, and then releasing the SET switchLASerLIMitI4 LASLIMI4?LASerLIMitMDP? LASerLIMitMDPMDP LAS LIM LASerLIMitV LASerLIMitV?MDI LAS IPD LASerMDILASerMDI? MDP P PD setpoint would be usedLASerMDLN? LASerMDLNLAS Mdln LASerMDP? LASerMDPMDP LAS LASerMODE? LAS ModeLAS Mode Ihbw LASerMODEIHBWLASerMODEMDP LAS Mode MDPLASerMODEILBW LasmodeilbwLASerOUTput? LASerOUTputLAS OUT LAS RAN LASerRANgeLASerRANge? LASRAN?LASerSETLDI? Where the response is the constant I setpoint value, in mA30 µA, for use in constant P mode with Calpd = LASerSETMDI?LASerSTEP Where the response is the constand PPD setpoint, in mWLASerSETMDP? 100 µALASerTOLerance LASerTOLerance commandLASerSTEP? LAS TOLSecond is the time window, in seconds LASerTOLerance?MESsage MESMESsage? RADixRAD Term 0 command is sent or the LDX-3232 is powered offRADix? Means hexadecimal, and OCT means octalTime clock is independent of the Timer clock LDX-3232 was last powered upTime Last TIMER? query is returned Since the last TIMER? query was issuedTimer Seconds since the last TIMER? query was issuedFunctions and Features Saving and Recalling from the Front PanelUsing the Laser Compliance Voltage Adjustment Saving and Recalling Under Remote OperationUsing the LDX-3232 Current Source’s Trigger Function LDX-3232 Rear PanelModulating the Laser Current Source BNC Interlock Usage ExampleModulating the Laser Current Source Functions and Features Calibration and Troubleshooting Calibration OverviewRecommended Equipment Description Manufacturer/Model SpecificationDMM Range Local Calibration of the LDX-3232 Current SourceCurrent Source Calibration Current LimitIPD Current Calibration Set equal to zero Constant powerCAL PD IPD Setpoint2000 mA Laser ModeLaser Forward Voltage Measurement Calibration Set to FS full scale of rangeRemote Calibration of the LDX-3232 Current Source Gpib CommandLimit Lasldi nrf value command IPD Setpoint Function State Gpib Command EEPROM, Lllll will be displayed on the display the laser Troubleshooting GuideGeneral Current source must be recalibratedFeature can be defeated via the Lasenableoutoff Command101 Response Message
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