Keysight Technologies Programming Keysight Technologies Continuous-Sweep Tunable Lasers. Application Note

Transcription

1 Keysight Technologies Programming Keysight Technologies Continuous-Sweep Tunable Lasers Application Note

2 Introduction The Keysight Technologies 8160x-series and 819x0-series tunable laser instruments are designed especially for making fast high-resolution spectral measurements by sweeping the output signal wavelength at a fixed speed, synchronized with detection instruments like optical power meters. The laser measures and logs the wavelength values during the sweep with a chosen interval and outputs electrical output triggers to synchronize detection sampling. The resulting arrays of wavelength and detected signal samples provide a spectrum showing the wavelength dependence of the device under test (DUT). Multiple detection channels can record signals at the same time for parallel measurements of multiple devices or devices with multiple output ports. Typical fiberoptic components measured this way include wavelength filters and multiplexers as well as wavelength selective switches. Most often these spectral measurements are made using Keysight optical power meters for detection, either modular sensors that can be installed in the same mainframe as the laser module or standalone instruments like the N774x-series multiport power meters. This kind of setup can be realized very conveniently and often most powerfully using software measurement engines from the N7700A Photonic Application Suite. This software provides simple start-up and operation, optimal use of the instrument functionality and also supports extensions for determining polarization dependence, detecting photocurrent from integrated optical-to-electrical devices as well as providing a graphic interface and functions for analysis. And the software engines can be automated using the COM interface. But in some cases, it can still be desirable to use customized automation software using instrument-level programming commands, as when coordinating the laser with other instruments or device controllers. This application note explains use of the instrument-level SCPI commands for programming swept-wavelength measurements and is intended as a companion to the 816x Programming Guide. Some special attention is paid to some newer functionalities available with the 81606A.

3 03 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Basics of programming 816x and N77xx instruments As a brief introduction, this section gives an overview of how your program can send instructions to the instruments. This can generally apply to many of the typically used programming languages or environments. Physically, the 8163B and 8164B mainframes have interfaces for connection to the controller PC via GPIB (general purpose interface bus) and via LAN. (Some earlier units do not include the LAN interface.) Most of the N77xx instruments have these interfaces plus USB 2.0. The N778xB polarization instruments have GPIB and USB 1.1. (Direct programming of the N778xB instruments is best done somewhat differently and will not be addressed in this document.) GPIB connections require the addition of a GPIB interface to the PC, either by installing an interface card or with a USB/GPIB adapter like the 82357B. The configuration details for a LAN connection depend on the network details. Refer to the instrument manuals for further information. Communicating with instruments over these physical interfaces is best handled in most programming environments by using the application programming interface VISA (Virtual Instrument Software Architecture). VISA is an industry standard that provides software library functions for communication with instruments, which are assigned individual VISA addresses, like GPIB0::20::INSTR. Keysight s implementation of VISA is included in the IO Libraries Suite, which provides other utilities and documentation as well as the Connection Expert software for managing instrument connections and addresses. The IO Libraries Suite also provides installation of the USB driver used by the N774xA instruments as well as Keysight GPIB interface drivers, so this software should be installed before initial connection of the instruments. Programming commands and queries can now be sent and responses can be read using the VISA interface. These commands and queries are the instrument-level SCPI text strings that are described in the instrument programming guides. All of the programming can be done at this level and that is the main topic of this document. Some other tools exist to simplify or enhance automation as well, which are briefly described here. A new powerful tool for generating the SCPI command syntax is the Keysight Command Expert, which also includes the information of the Programming Guide for each command and also helps with the handling of binary block data. Instruction sets are available for both the 816x and N77xx platforms. The 816x VXI Plug&Play driver has been very popular for automating these instruments. The driver provides convenient functions to the programming environment that then generate the SCPI code with the correct syntax. This can be especially convenient in graphical environments like VEE or LabVIEW. (Note that LabVIEW supports use of the VXI Plug&Play style drivers with wrapper files that can be generated for the corresponding driver and LabVIEW versions with the Instrument Driver Import Wizard utility, available from National Instruments.) The 816x Plug&Play driver is particular powerful because beyond generating single SCPI commands it also offers advanced application functions for synchronizing a tunable laser and power meters for swept-wavelength measurements. It also simplifies reading the logged data arrays that are tranferred in binary block format. As it is based on a legacy platform, it does impose some limitations on the newest instruments, such as limiting the maximum power array to 100k samples and the maximum sweep rate to 80 nm/s. Finally, Keysight offers application software for swept-wavelength measurements within the N7700A Photonic Application Suite. These measurement engines include server components that can be automated over a COM interface. Using this software can be the quickest and most effective way to automate the equipment. These engines, as well as the other necessary software components can be installed and managed using the Photonic Applications Package Manager.

4 04 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Principle of swept-wavelength measurements There are built-in functions for wavelength sweeps with the tunable lasers. The sweeps can run in stepped sweep mode or in continuous sweep mode. In both modes the laser will move between a chosen start wavelength and a higher chosen stop wavelength. A third wavelength parameter defines the step width. In stepped mode, the laser moves over the chosen wavelength range in a series of steps. The laser stabilizes the wavelength at each step. It can dwell at each wavelength for a pre-selected period or wait for a trigger or command for the next step. The laser can output a trigger when each wavelength step is finished. In continuous mode, the sweep begins by accelerating outside the chosen wavelength range to the given sweep speed. The wavelength then scans at this speed between the start wavelength and stop wavelength without interruption before stopping. The laser can be programmed to output a trigger at the time of each step, using a trigger interval deterimined by the sweep speed and the step width. Note that the wavelength margin required for acceleration and deceleration increase with the sweep speed. Compared to earlier models, the 8160xA family accelerate faster, allowing fuller use of the total tuning range, even at high speed. The lasers use a built-in wavelength monitor to achieve the specified wavelength accuracy. In stepped mode, this monitor provides feedback to regulate each step to the intended wavelength. In continuous mode, the wavelength value can be captured for each trigger point and logged into memory. In both modes, the output power of the laser is regulated to a constant power during the sweep. Spectral power measurements are made by using the laser step triggers to synchronize sampling by the optical power meters. The power meters are programmed to log the correct number of samples for the sweep, with an averaging time for each sample not greater than the dwell time for stepped mode or the trigger interval in continuous mode. After the sweep, the logged power data and the wavelength data are used to construct the spectrum. Often the goal of such a measurement is to determine the influence on this spectrum of including a device under test into the optical path, comparing to a reference measurement without DUT to determine the insertion loss. In this case, the result is a relative power vs. wavelength trace. The stepped sweep mode is simple to implement and could even be automated by repeating simple commands to advance the wavelength and then reach the power sample. Even using the built-in sweep function, there is extra time used to move and stabilize the wavelength when the power meter is not sampling, roughly on the order of 1 s per point. (That is reduced to about 0.3 s in the new 8160xA models.) But for high-resolution measurements, for example 5 pm steps over 50 nm with 10,001 points, that is prohibitively slow. Continuous sweep mode eliminates most of the dead time. For example, the 81606A can sweep this range at 200 nm/s. That takes about 0.5 s, with the power meter averaging for 25 µs per point. Even with some overhead time including acceleration, data transfer and processing, the time saving is enormous. Using the N7700A FSIL software and the 81606A, the cycle time for repeating such measurements is about 1.2 s using one-way sweeps and about 0.7 s with two-way sweeps! Continuous-sweep measurements also have the significant advantage that the power samples average over a chosen interval of wavelength. This effective linewidth broadening significantly reduces fluctuations in the sampling results that can be caused by coherent interference with multiple-reflection paths in the DUT or setup. Instruments capable of continuous sweep measurements include: 81606A, 81607A, 81608A, 81600B, and earlier-generation modules for Slot 0 of the 8164B platform, as well as the 81960A, 81940A and 81980A compact modules. Instruments that do not provide regulated continuous sweeps but do make stepped sweeps include: 81949A, 81989A and 81609A. The 81950A, N7711A and N7714A tunable sources do not have wavelength sweep functionality.

5 05 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Instrument-level programming for continuous sweep measurements Most of the commands used to run the tunable lasers are listed under the Signal Generation: The SOURCE subsystem section of Chapter 4, Measurement Operations & Settings in the programming guide. For example, the command to start a sweep is command: [:CHANnel[m]]:WAVelength:SWEep:[STATe] syntax: [:CHANnel[m]]:WAVelength:SWEep:[STATe]<wsp>STOP 0 STARt 1 PAU Se 2 CONTinue 3 The square brackets indicate optional parts that can be omitted if not relevant or if the default will be used. In this case, the SOURce parameter n, which indicates the slot number of the tunable laser, can be omitted if only one laser is present in the addressed instrument. The tunable lasers do not currently use the CHANnel parameter and will ignore it. Commands can be sent with the full spelling or shortened to the form indicated with the capital letters. Parameter values are given after a blank space indicated by <wsp> and possible values are shown separated by the vertical bar. So a sweep could be started with equivalent forms including the following. source0:wavelength:sweep:state start sour0:wav:swe 1 wav:swe 1

6 06 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Before starting a sweep, the necessary instrument settings and sweep parameters must be configured. The following list shows the most commonly needed instructions. Line breaks in the commands are due to this document formatting and should not be include in the program. Label Command Example Comment A1 :LOCK lock 0,1234 unlock the safety to enable laser; may be done manually A2 :OUTPut[n][:CHANnel[m]]:PATH outp:path lows only for lasers with 2 output ports, to choose between low SSE and high power ports A3 :TRIGger:CONFiguration trig:conf loop if power meter modules are included in the mainframe with the laser, this routes output triggers from the laser to the input triggers of the power meters A4 [:CHANnel[m]]:POWer:STATe sour0:pow:stat 1 switch laser output on; this process can take a few seconds for regulating A5 [:CHANnel[m]]:POWer:STATe? sour0:pow:stat? this query can be used to hold the program until the laser state is ready, when it responds; the program may need to extend the default timeout A6 :TRIGger[n][:CHANnel[m]]:OUTPut trig0:outp stf configure laser output triggers for step finished A7 :TRIGger[n][:CHANnel[m]]:INPut trig0:inp sws this setting allows the sweep to wait for a hardware or software trigger before beginning, after all configuration commands are sent A8 A9 A10 A11 A12 A13 A14 A15 A16 A17 A18 [:CHANnel[m]]:WAVelength:SWEep:STARt [:CHANnel[m]]:WAVelength:SWEep:STOP [:CHANnel[m]]:WAVelength:SWEep:SPEed [:CHANnel[m]]:WAVelength:SWEep:MODE [:CHANnel[m]]:WAVelength:SWEep:LLOGging [:CHANnel[m]]:WAVelength:SWEep:PMAX? [:CHANnel[m]]:POWer[:LEVel] [:IMMediate][:AMPLitude[l]] [:CHANnel[m]]:WAVelength:SWEep:STEP:[WIDTh] [:CHANnel[m]]:WAVelength:SWEep:CHECkparams? [:CHANnel[m]]:WAVelength:SWEep:EXPectedtriggers? [:CHANnel[m]]:WAVelength:SWEep:[STATe] sour0:wav:swe:star 1525nm sour0:wav:swe:stop 1565nm sour0:wav:swe:step 5pm sour0:wav:swe:spe 40nm/s sour0:wav:swe:mode cont sour0:wav:swe:llog 1 sour0:wav:swe:chec? sour0:wav:swe:pmax? 1525nm,1565nm sour0:pow 10dbm sour0:wav:swe:exp? sour0:wav:swe 1 sets the sweep start wavelength sets the sweep stop wavelength sets the sweep step width sets the sweep speed select continuous sweep mode enables logging of swept wavelength values this query can be used to confirm a consistent set of sweep parameters for the instrument this query can be used to find the maximum power available for the chosen wavelength range and sweep speed; returned in units W. select laser output power below maximum available power this query can be used to find the number of output triggers from the sweep, which can be used to program the data acquisition of the power meters (returns signed integer) this activates the sweep function, which can start immediately or wait for an input trigger, as configured above

7 07 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note To program optical power meters for the measurement, the following set of configurations should be made, normally before Step A18 of the above table. In general, these are each applied to all used power meters, as by repeating the commands with all relevant slot numbers. Label Command Example Comment B1 :TRIGger[n][:CHANnel[m]]:INPut trig1:inp sme set input trigger mode to single measurement, giving one sample per trigger B2 :SENSe[n]:[CHANnel[m]]:POWer:UNIT sens1:pow:unit 1 set for linear power units, Watts; usually preferred B3 :SENSe[n]:[CHANnel[m]]:POWer:RANGe:AUTO sens1:pow:rang:auto 0 disable autoranging (not usable during logging) to select range manually B4 :SENSe[n]:[CHANnel[m]]:POWer:RANGe[:UPPer] sens1:pow:rang 10dbm choose the lowest power range that will not clip the strongest expected signal level B5 :SENSe[n]:[CHANnel[m]]:POWer:RANGe[:UPPer]? sens1:pow:rang? this query can be used to hold the program until the range setting is finished, when it responds B6 :SENSe[n]:[CHANnel[m]]:POWer:WAVelength sens1:pow:wav 1550nm B7 :SENSe[n] [:CHANnel[m]]:FUNCtion:PARameter:LOGGing sens1:func:par:logg 8001,100us the particular wavelength value is not significant for relative measurements, normalized to a reference sweep, but the value should be constant for sweeps to be compared enter the parameter for the logging function with the number of points matching the expected triggers and the averaging time not more than the step trigger interval If the power meters are in a separate instrument from the tunable laser, then the BNC trigger output should be connnected with a cable to the power meter BNC trigger input. The following command to start the logging function is shown here separately, because in the case of multiple power meters, it is recommended to configure all power meters before starting the logging on any of them. This can be important for multiport power meter instruments like the N7745A. Label Command Example Comment C1 :SENSe[n][:CHANnel[m]]:FUNCtion:STATe sens1:func:stat logg,star set input trigger mode to single measurement, giving one sample per trigger Before next sending a trigger to the laser, it should be confirmed that the sweep is waiting for the trigger. Label Command Example Comment D1 D2 [:CHANnel[m]]:WAVelength:SWEep:FLAG? [:CHANnel[m]]:WAVelength:SWEep:SOFTtrigger sour0:wav:swe:flag? sour0:wav:swe:soft this query should be repeated until the response is +1 or a higher uneven integer (returns signed integer) this command triggers the sweep without sending the same trigger to the power meters The laser now accelerates to the chosen sweep speed and outputs triggers at the chosen interval. The program can wait for the expected sweep time and then poll the instruments for readiness to upload the data. Typically the power meter is ready first, as soon as the last expected trigger is received, while the laser completes processing of the wavelength data. So a good sequence is the following. Label Command Example Comment E1 :SENSe[n][:CHANnel[m]]:FUNCtion:STATe? sens1:func:stat? this query is repeated until the response changes from LOG- GING_STABILITY,PROGRESS to LOGGING_STABILITY,COMPLETE E2 :SENSe[n][:CHANnel[m]]:FUNCtion:RESult? sens1:func:res? this query is used for each power meter to upload the data arrays; the data format is described below E3 [:CHANnel[m]]:WAVelength:SWEep:FLAG? sour0:wav:swe:flag? After E2 or in a parallel thread, this query is repeated until the flag from the laser is incremented by 1 or 2 from the value returned at D1 E4 [:CHANnel[m]]:READout:DATA? sour0:read:data? llog this query uploads the lambda logging data; the format is described below E5 [:CHANnel[m]]:WAVelength:SWEep:[STATe]? sour0:wav:swe? this query can be repeated until the response is +0 for the full sweep operation to complete before sending new instructions to the laser As configured above, the single sweep measurement is now finished for the instruments. To repeat sweeps with the same parameters, it is sufficient to repeat step A18 and then continue from C1 again. (For 819x0A lasers, repeat both 13 and A18)

8 08 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Data format The resulting data are an array of 64-bit real number laser wavelength values and a corresponding array of 32-bit optical power values from each power meter. The data are transmitted in binary block format, as described in the Programming Guide. Expressing this binary data as real arrays requires attention to the byte ordering. The first few bytes represent ASCII characters. The first is the symbol #, followed by a digit that gives the remaining number of bytes to interpret as characters. These give a number that tells how many bytes of data follow. For example, # indicates 808 bytes of data are contained, corresponding to bit wavelength values or bit power values. Each value is transmitted least significant byte first (LSBfirst, little-endian, Intel byte order ). So for example, 8 bytes, shown in hexadecimal notation, received as c2 ba 43 e5 57 ab b9 3e is about 1.53E-9, or 1530nm. (Using the wrong ordering gives values with dramatically varying magnitude. This example gives about -2.9E13!) The Command Expert instrument command sets or the 816x Plug&Play driver simplify programming with automatic reading of binary blocks, providing the correct formatting. Or using direct IO with VEE, LSB can be selected for the byte ordering in the Instrument Manager under Advanced Instrument Properties and the binary block format can be selected for automatic parsing during the read operation. Other programming environments use other ways to format the input data. In some cases, it may be most convenient to handle reading and parsing of binary blocks at the lower VISA level. That is supported by the VISA COM I/O with its IFormattedIO488 interface, setting the property InstrumentBigEndian to false and using the READIEEEBlock method. For the power meters, the parameter type is set to BinaryType_4 and for the wavelength data to BinaryType_8. Wavelength data details The power vs. wavelength traces are often compared with another to calculate spectra of relative parameters like insertion loss. It is then very useful to interpolate the traces, to fix the wavelength values to the grid defined by the chosen start and step wavelengths. This interpolation to equidistant wavelengths is another convenient feature of using the 816x Plug&Play driver MFLambdascan functions or the N7700A measurement engines. These advanced application software products also include the influence of the averaging time and analog bandwidth of the power meters on the wavelength interval represented by each sample. Especially when the trace is to be interpolated to the grid of the chosen sweep settings, it is advisable to extend the wavelength settings on the instrument slightly beyond the desired wavelength range, since the actual measured wavelengths at the trigger points can be lower or higher than the intended value. This offset can be up to a few tens of picometers, depending on laser model and the sweep speed, so a range extension of 0.1 nm is usually sufficient. Periodic use of the lambda zeroing function of the tunable laser reduces this offset as well. The 81600B model applies this function settling automatically when the instrument temperature has changed. This autocalibration can be disabled when it would otherwise interrupt the measurement flow, so that lambda zeroing can instead be applied at chosen times. On other models, like the 81606A and 81960A, the temperature dependence can by handled more dynamically and the autocalibration function is not used. It is still advisable to apply lambda zeroing periodically, to reduce the wavelength offset and as a simple maintenance procedure that distributes lubrication over the full mechanical tuning range. In any case the offset does not influence the accuracy of the measured wavelength values. The relevant commands are: [:CHANnel[m]]:WAVelength:CORRection:AUTocalib [:CHANnel[m]]:WAVelength:CORRection:ZERO

9 09 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Dynamic range and stitching Some components, like wavelength domain multiplexers (WDM), can yield traces that vary over a wide power range between the passbands and rejection bands. These can exceed the dynamic range of the power meters, when they are logging data at a fixed power range setting. The range setting determines the maximum measurable power level, which is typically 3 db higher than the range setting. For example, the 0 dbm range can return values up to about +3 dbm or 2 mw. The dynamic range extends from this power value down to the level of the noise, which depends on both the range setting and the averaging time and can be limited. This power range setting corresponds to the gain of the transimpedance amplification following the detecting photodiode. This amplification produces a voltage for the analog to digital conversion that is linearly proportional to the photocurrent for optimal linearity and zero-level stability. In order to increase the dynamic range of the measurement, the sweep can be repeated a second or even third time at progressively more sensitive power range settings. The resulting traces can then be used to construct a stitched trace that uses the most appropriate sweep result for each segment of the wavelength range. This procedure also benefits from the interpolation to equidistant points and accomodation of any bandwidth differences between the power meter ranges and is provided automatically in the 816x MFLambdascan and N7700A measurement engine routines. The N7744A and N7745A power meters have an additional functionality that allows switching some additional amplification gain dynamically during the sweep (autogain) and thus increasing the measurement dynamic range with a single sweep. This is active and transparent by default, providing the maximum range for the measurements. In some cases a rapidly oscillating power level, as from an amplitude modulation or when measuring extinction of a polarizing component with the fast-switching N7786B polarization controller, can interfere with the operation of the autogain. In such cases, the function can be easily disabled. :SENSe[n][:CHANnel[m]]:POWer:GAIN:AUTO example: sens1:pow:gain:auto 0

10 10 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Fast repetition Quickly repeated sweeps with identical sweep parameters are sometimes needed, as for alignment and calibration procedures, where the DUT is adjusted each time, possibly with feedback from the previous measurement. Multiple sweeps with different polarization controller settings or with different power range settings for stitching are other cases. For this purpose, the cycles setting can be used to allow multiple sweeps without repeatedly activating the sweep function as in A18. For a fixed number of repeated sweeps, that number of cycles can be chosen. Or the value zero, 0, can be used for an indefinite number of repetitions. When the laser input trigger is configured for sweep start, as in A7 above, the laser will wait each sweep for the next trigger. The Flag query can then be used both to determine when the lambda logging data are ready and when the laser is ready to start the next sweep. Some newer laser models, like the 81606A and 81960A, now also support continuous sweeps in both directions, which can be used to reduce the time until the laser is ready for the next sweep and thus increase the repetition rate as well. The laser will remain in sweep mode until the chosen number of sweeps are completed or the sweep mode is stopped by command. Most commands to the laser should not be sent while the sweep mode is active. Relevant commands are: [:CHANnel[m]]:WAVelength:SWEep:CYCLes example: sour0:wav:swe:cycl 0 [:CHANnel[m]]:WAVelength:SWEep:REPeat example: sour0:wav:swe:rep twoway [:CHANnel[m]]:WAVelength:SWEep:[STATe] example: sour0:wave:swe 0 Similar to the ability of the lasers to run repeated cycles while the sweep function is active, the N774x optical power meters can be programmed to log multiple sets of samples. This is achieved by using the loop parameter. In this way, the next sweep can begin without new instructions to the power meter, as soon as the laser begins sending triggers. The main repetition rate advantage comes in the case that the laser is ready for the next sweep before all the data has been uploaded from the power meters. When using the loop function, the power meters can record new data in a second memory buffer, while data from the previous loop is available and can be simultaneously uploaded from the first buffer. This can be a valuable feature when many samples are taken and two-way sweeping is used. In this mode, the query of E1 should be replaced with a query of the loop index, which is incremented when a loop is completed. Note however that the logging function must be stopped before changing power ranges. The relevant commands are: :SENSe[n][:CHANnel[m]]:FUNCtion:LOOP :SENSe[n][:CHANnel[m]]:FUNCtion:RESult:INDex? As an achievable performance indication: the N7700A FSIL software, combining these methods for quick repetitions and for high dynamic range, can repeat measurements with more than 75 db dynamic, and 50 nm range at 5 pm resolution in less than 1.8 s. That uses the 200 nm/s two-way sweeps of the 81606A together with the N7744A, stitching sweeps with the +10 and -20 dbm power ranges using 25 µs averaging time.

11 11 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Figure 1. Stitched measurement over 50 nm with >75 db range in 1.7 s. Wavelength responsivity calibration During the sweep logging, the power meters are set to a fixed wavelength, This means that the uploaded power values are not calibrated for the detector wavelength responsivity over the swept wavelength range. This is not important for measuring relative parameters like insertion loss, where the trace is compared to a reference trace calculated with the same fixed wavelength responsivity value. But in some cases, more accurate results can be obtained by using the spectral wavelength responsivity data that are stored on the power meters. For example, a measurement of the wavelength dependent responsivity of a device with integrated photodiode should determine the photocurrent from a known optical power. So the input optical power should be measured accurately during the sweep. Or in some cases, a reference trace from one power meter should be applied to other power meters that may have different responsivity spectra. For such cases, the calibration data, stored as inverse responsivity, can be uploaded by the program. Then the power data in the trace can be calibrated using the ratio of the calibration data at the wavelength of the trace point and at the wavelength value used during logging. The command to upload the data, :SLOT[n][:HEAD[m]]:WAVelength:RESPonse? returns the data as a binary block, with pairs of 4-byte real numbers for the wavelength and calibration factor. The factor is multiplied by the internal signal voltage to give the applied optical power, so the factor is higher when the responsivity is lower. Typically the values are saved at 2 nm intervals, so interpolation is required for normalizing traces with narrower steps. Most of the power meters use InGaAs detectors to provide relatively flat responsivity across the wavelength range used with single-mode fiber. The N7700A-100 IL/PDL software can measure device responsivity and uses this calibration data.

12 12 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Power meter sweep parameters Power meter Averaging times Ranges/Bandwidth (10 db increments) N7744A, N7745A 1 µs to 10s, 2µs granularity to 1ms, then ca. 0.1% granularity N7747A, N7748A 25, 100, 200, 500µs, 1, 2, 5, 10, 20, 50, 100, 200, 500ms, 1, 2, 10s 81636B 25, 100, 200, 500µs, 1, 2, 5, 10, 20, 50, 100, 200, 500ms, 1, 2, 10s 81634B 100, 200, 500µs, 1, 2, 5, 10, 20, 50, 100, 200, 500ms, 1, 2, 10s 81635A 100, 200, 500µs, 1, 2, 5, 10, 20, 50, 100, 200, 500ms, 1, 2, 10s +10dBm 240kHz to -10dBm 240kHz -20 dbm 130kHz -30dBm 10kHz +10dBm 5kHz to -20 dbm 5kHz -30dBm 4kHz -40dBm 4kHz -50dBm 300Hz to -70dBm 300Hz +10dBm 17kHz to -20 dbm 17kHz +10dBm 5kHz to -20 dbm 5kHz -30dBm 4kHz -40dBm 4kHz -50dBm 300Hz to -70dBm 300Hz +10dBm 5kHz to -20 dbm 5kHz -30dBm 4kHz -40dBm 4kHz -50dBm 300Hz -60dBm 300Hz 81630B +30dBm 3.5kHz to 0dBm 3.5kHz -10dBm 3kHz -20 dbm 3kHz -30dBm 300Hz to -50dBm 300Hz Single-range dynamics in 0 dbm Range, 100 µs averaging (approx.) Logging Samples 60 db 1M/port + 1M/port buffer 50 db 1M/port + 1M/port buffer 55 db 100K 40 db 20K 40 db 20K 40 db 20K 81623B +10dBm 3.5kHz max 37 db 20K 81624B +10dBm 5 khz max 37 db 20K 81626B +30dBm 5 khz max 37 db 20K 81628B +40dBm 3.5kHz max 37 db 20K

13 13 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Tunable laser sweep parameters Laser models 81606A 81607A 81608A Sweep speeds (nm/s) 0.5, 1, 2, 5, 10, 20, 40, 50, 80, 100, 150, 160, B 81640B, etc A 0.5, 1, 2, 5, 10, 20, 40, , 1, 2, 5, 10, 20, 40, 50, 80, 100, 200 Two-way sweeps yes no yes no 81940A 81980A Max. step rate 1 MHz 40 khz 1 MHz 40 khz Max. lambda points 100k 100k 100k 100k 0.5, 1, 2, 5, 10, 20, 40, 50 Debugging And finally to finish, here are a few tips you might have needed at the beginning! If the program stops at the wrong point, it may leave the sweep or logging functions active. This can interfere with starting the program again, so it can be useful to start the program with commands to stop the logging on the power meters and the sweep on the laser. Using the preset commands at the beginning of the program also help assure a known condition at the start. For example, the Loop parameter of the N774x instruments should normally be kept at the default value of 1 for all ports, if the status is not being checked with the index query. This parameter can be reset directly or with the preset command. The code returned by the Checkparams query at A14 give details about conflicts in the sweep parameters, as detailed in the Programming Guide. These can be used to correct the settings, if there is a problem. Some actions, like enabling the laser and setting wavelength can require extended time and the Timeout setting of the program may need to be increased. Since query responses will usually be strings, attention may be need to whether a response is signed, e.g. 0 or +0. Useful references 8163A/B, 8164A/B & 8166A/B Mainframes Programming Guide, B65 N77xx Series Programming Guide, N C01 VISA Help and VISA COM Help, distributed with Keysight IO Libraries Suite 816x VXI Plug&Play Driver Help, distributed with the Keysight 816x driver N7700A user guides, distributed with Keysight N7700A software N77xx Series Getting Started Guide, N A01, especially for LAN connection details Transient optical power measurements with the N7744A and N7745A, application note: EN

14 14 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Download your next insight Keysight software is downloadable expertise. From first simulation through first customer shipment, we deliver the tools your team needs to accelerate from data to information to actionable insight. Electronic design automation (EDA) software Application software Programming environments Utility software Learn more at Start with a 30-day free trial.

15 15 Keysight Programming Keysight Technologies Continuous-Sweep Tunable Lasers - Application Note Evolving Since 1939 Our unique combination of hardware, software, services, and people can help you reach your next breakthrough. We are unlocking the future of technology. From Hewlett-Packard to Agilent to Keysight. For more information on Keysight Technologies products, applications or services, please contact your local Keysight office. The complete list is available at: Americas Canada (877) Brazil Mexico United States (800) mykeysight A personalized view into the information most relevant to you. Register your products to get up-to-date product information and find warranty information. Keysight Services Keysight Services can help from acquisition to renewal across your instrument s lifecycle. Our comprehensive service offerings onestop calibration, repair, asset management, technology refresh, consulting, training and more helps you improve product quality and lower costs. Keysight Assurance Plans Up to ten years of protection and no budgetary surprises to ensure your instruments are operating to specification, so you can rely on accurate measurements. Keysight Channel Partners Get the best of both worlds: Keysight s measurement expertise and product breadth, combined with channel partner convenience. Asia Pacific Australia China Hong Kong India Japan 0120 (421) 345 Korea Malaysia Singapore Taiwan Other AP Countries (65) Europe & Middle East Austria Belgium Finland France Germany Ireland Israel Italy Luxembourg Netherlands Russia Spain Sweden Switzerland Opt. 1 (DE) Opt. 2 (FR) Opt. 3 (IT) United Kingdom For other unlisted countries: (BP ) DEKRA Certified ISO9001 Quality Management System Keysight Technologies, Inc. DEKRA Certified ISO 9001:2015 Quality Management System This information is subject to change without notice. Keysight Technologies, 2017 Published in USA, December 1, EN