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40

Chapter 6. Optical switch

the sequence returns to that channel, and will remain constant when

different channels are being measured.

To configure multi-channel

PID

feedback:

1.

Deselect any dark ports.

2.

Before trying to

PID

lock a laser, make sure it has a good mode-

hop-free range around the desired wavelength/frequency.

3.

Configure each laser/port in turn as described in chapter 5.

Disable

PID

locking for each before setting up the next.

Note

that when

PID setup

is pressed for a given port, the switch

will select that port and stop auto-stepping to provide the best

response times for adjusting the

PID

parameters.

The time-series window is very useful to monitor the wave-

length while configuring the

PID

locking parameters, provided

auto-stepping is not enabled.

4.

When all ports/lasers are locking individually, with

PID

feed-

back

off

for

each,

start

auto-stepping.

The

exposure

time

should be short compared to the dwell time; for example, 1 ms

exposure and 100 ms dwell time.

5.

Enable

PID

for each laser in turn, making sure the laser adjusts

to the correct wavelength before enabling the next.

Summary of Contents for FSW4

Page 1: ...Fizeau Wavemeter and Fibre Switcher FZW600 FSM2 FSW4 FSW8 Firmware v0 9 5 mogfzw v1 4 5 ...

Page 2: ...quential damages in connections with or arising out of the performance or use of any of its products The foregoing limitation of liability shall be equally applicable to any service provided by MOGLabs Copyright Copyright MOG Laboratories Pty Ltd MOGLabs 2017 2022 No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechan...

Page 3: ...Device UI 7 3 2 Web UI 8 3 3 Software UI 9 4 Operation 13 4 1 Fringe identification and optimisation 13 4 2 Auto exposure algorithm 16 4 3 Fast mode 16 4 4 Pulsed laser measurement 16 4 5 Externally triggered mode 17 4 6 Measurement averaging 17 4 7 Calibration adjustment 18 5 PID locking 21 5 1 Using with MOGLabs DLC laser controller 22 5 2 PID parameters 22 5 3 Integrator windup 24 5 4 Examples ...

Page 4: ...36 A Specifications 41 B Firmware updates 45 C Command language 47 C 1 General functions 47 C 2 Display 48 C 3 Measurement 48 C 4 Camera 49 C 5 Optical switch 50 C 6 Control voltage out and PID 52 D Errors and troubleshooting 55 E Communications 57 E 1 Protocol 57 E 2 TCP IP 57 E 3 USB 59 F Dimensions and PCB 61 F 1 Connectors 64 ...

Page 5: ... expense of reduced accuracy 1 4 FSW Fibre switch If using a fibre switch connect the out put fibre from the switch to the input fibre port on the FZW Electrically connect the FSW and FZW using the supplied M8 cable Connect your light source via fibre to one of the 4 or 8 input ports on the FSW 5 Input light with the supplied free space to fibre adapter Typ ically the FZW only needs a few microwat...

Page 6: ... to ensure reliable measurement Typically the FZW will reach thermal equilibrium and full accuracy within 15 minutes of being turned on The most accurate results will be obtained in a well stabilised lab environment It is recommended that the FZW not be in thermal contact with any other equipment to prevent formation of thermal gradients Host connection The recommended mode of operation is using t...

Page 7: ...gth Figure 1 1 Collimated monochromatic laser light and Fizeau etalons cre ate interference patterns on an imaging detector The wavelength is calcu lated by combining measurements of the fringes from four different etalons A rough estimate of the wavelength is obtained directly from the fringe spacing to an absolute accuracy of one part in 100 This initial estimate is then improved by the phase of...

Page 8: ...other wavemeters as a calibration source The FZW also integrates a modern 32 bit microprocessor and high resolution compact colour display Wavelength calculation is per formed automatically on the device so that no host computer is required It is compact and can be powered from USB or even a rechargeable battery so you can move it around your lab and mea sure wavelength right where you are adjusti...

Page 9: ...ront panel layout The buttons are arranged with up down left and right buttons and an additional OK button in the centre In wavelength display mode the up down buttons change the display units and the left right but tons swap between different diagnostic modes see 3 1 Pressing OK opens the menu system The display includes a sleep mode which reduces the brightness when not in use Where this feature...

Page 10: ...l device error LOCK Off PID analogue output disabled Green PID locked Yellow PID engaged but not locked Red PID output saturated Blue Analogue output error 2 1 1 Menu system The menu system allows for interactive control of the device without a computer interface Figure 2 2 It is started by pressing the OK button from the measurement display mode and exiting by pressing the left directional button...

Page 11: ...fies this digit and using the left right keys changes which digit is selected Pressing OK again exits edit ing mode In particular it is useful for configuring the Ethernet settings in an networking environment where DHCP is disallowed Figure 2 3 In this situation an appropriate static IP should be allocated to the unit the gateway set as required by the network configuration and DHCP set to OFF Fi...

Page 12: ...to 30 V for Rev4 devices USB Standard USB type B connector for powering and or communicating with the device When used to power the device must be connected to a USB port capable of supplying 600 mA Ethernet RJ 45 jack for 10 100 MB s TCP IP communications which is the recommended interface for computer control and monitoring PID Analogue output port for wavelength monitoring or PID control of las...

Page 13: ...e saturation is a measure of the optical power reaching the de tector and the contrast is a measure of fringe quality In general higher saturation is preferred as this permits faster measurement however oversaturation as indicated by the bar turning red will degrade measurement accuracy Pressing the left right buttons changes to an alternate display mode Figure 3 2 permitting diagnostic of the fri...

Page 14: ... for monitoring the de vice remotely through a web browser such as using a smartphone Navigating to the device IP address displays the currently recorded wavelength which is automatically updated Figure 3 3 At present this interface doesn t provide control options but increased func tionality will be provided in future firmware updates Figure 3 3 Demonstration of the integrated web interface showi...

Page 15: ... Windows operating systems is available from the MOGLabs website Most of the user interface is dedicated to displaying the etalon fringes which are important for measurement diagnostics see 4 1 Figure 3 4 Demonstration of the host software interface showing expo sure controls 1 convergence monitor 2 interference fringes 3 mea sured wavelength 4 display units selector 5 etalon temperature 6 and com...

Page 16: ...r wavelength is changing rapidly or the calibration has been perturbed the bars may exceed the indicated region indicating the reliability of the measured value is reduced 3 3 1 Time series measurement Time series opens a dialog that shows how the measured wave length is changing over time Figure 3 5 This can be beneficial for measuring long term drifts in laser wavelength and diagnosing PID locki...

Page 17: ...th measure ment is changing over time for measuring drift The graph displays Du ration seconds of data with a datapoint collected every Interval seconds When Averaging is enabled the wavelength measurements during each interval are averaged to enhance the measurement precision ...

Page 18: ... to measure the mode hop free scan range of a laser Setting the Interval to zero ensures measurements are recorded as rapidly as possible The measurement rante measurement mean standard deviation and peak to peak range are shown in the status bar at the bottom ...

Page 19: ...uring a measure ment can change the structure of the interference pattern and cause the measurement to fail Typically this is evident by the presence of secondary peaks in the fringes a significant widening of the peak widths and or a significant reduction in the amplitude of the fringes compared to the background level Figure 4 1 Multimode behaviour may be evident in only one of the etalons Figur...

Page 20: ... a non Gaussian beam shape that introduces bias and reduces accu racy of the measurement Single mode fibres are therefore strongly preferable where accurate measurements are required With multimode fibre the structure of the fringes fluctuates with both the fibre coupling alignment and mechanical strain on the fibre as can be seen by fluctuations in the measured wavelength when dis turbing the fib...

Page 21: ...causes measurement bias left Adjusting the input coupler alignment can give more uniform fringe heights right and more reliable measurement Figure 4 4 Examples of fringes measured with a 200 µm core fibre The mode shape makes reliable readout almost impossible left although in some situations a low accuracy measurement can still be achieved right ...

Page 22: ...ecessary to disable the auto expose feature 4 3 Fast mode The default measurement mode is suitable for most applications and provides a good general purpose trade off between measure ment speed and accuracy However in some situations it may be preferable to accept reduced accuracy to increase the measurement rate and reduce susceptibility to unstable or high linewidth laser input Engaging fast mod...

Page 23: ... pulsed mode and prevents errors arising from acquisi tions occurring without any incident light The FZW begins a measurement whenever the TTL input is low Hold ing the input low will immediately trigger a second measurement once the first is complete so it is recommended to hold the input high when not in use 4 6 Measurement averaging The FZW is capable of several hundred wavelength measurements ...

Page 24: ...e and pressuer Averaging can be enabled through the on device menu system or using the MEAS AVERAGE command Setting the value to zero disables the internal averaging Averaging can also be enabled in the time series window of mogfzw over the inspecified interval Operation of the FZW in environments with poor ambient temperature control can cause much more rapid drift and the benefit of data averagi...

Page 25: ...h as a neon lamp However often the accuracy of a wavemeter is only critical around a particular wavelength of interest and it is desirable to improve the calibration of the device around this wavelength even though this negatively impacts the absolute accuracy at other wavelengths To calibrate at a single wavelength connect a reference laser of stable wavelength to the FZW using a single mode fibr...

Page 26: ...rence frequency can be entered tion can also be applied programmatically using the MEAS CORRECT command Note that when adjusting the calibration it is recommended to use a well known reference e g atomic transition with an appropriate amount of averaging The calibration can also be reverted to the factory provided cali bration by ticking the appropriate box in the software interface or using the c...

Page 27: ... wavelength G is an overall gain and Voffset is a constant voltage offset The PID coefficients kp ki kd are floating point values in the range 0 1 which correspond to pro portional integral and differential terms respectively Typical values are G 10 V THz kp 0 ki 1 and kd 0 The offset allows the FZW to control unipolar devices such as the MOGLabs DLC controllers which have 0 to 2 5 volt control in...

Page 28: ...P S T U P N I T X E B L E N N A H C A L E N N A H C a i l a r t s u A n i e d a M r o t c e t e d o t o h P G I R T R E S A L k c o l r e t n I DLC Diode Laser Controller Figure 5 1 Stabilising a laser frequency with the FZW and PID The SMA output of the FZW should be connected to the SWEEP PZT input on the rear of the MOGLabs DLC controller 5 2 PID parameters The PID feedback signal is calculated...

Page 29: ...g ative gain can be used to invert the sign of the output voltage kp ki kd Proportional integral and differential coefficients each limited to a range of 0 to 1 Set ki kd 0 to use the analogue output as a measure of laser wavelength where kp and the gain G define the relationship between the output voltage and the measured wavelength relative to the setpoint wavelength λ0 Vmax Vmin These set the u...

Page 30: ...en the lock is engaged but the error signal has not converged to zero and red when the output has saturated indicating the lock has failed see also 2 1 5 3 Integrator windup Integrator windup is caused by saturation of an output actuator Once the FZW output voltage reaches the maximum or minimum value defined by Vmax or Vmin the integrator will continue to accu mulate error wind up but the actuato...

Page 31: ... output voltage will be directly proportional to the measured wavelength relative to the setpoint Figure 5 3 shows an oscilloscope trace of Vout for an FZW measuring the wavelength of a rapidly scanning laser for example to optimise the laser mode hop free tuning range Figure 5 3 Wavelength measurement of a scanning laser The gain was set to 0 5 V GHz and the ramp amplitude shows that the laser wa...

Page 32: ...ced gain via the SPAN control The net feedback gain will be the same but more of the DAC output range will be used The figures below show the locking response for a 780 nm MOGLabs cateye laser connected to a MOGLabs DLC controller The PID set tings are an overall gain of 0 5 V GHz kp kd 0 and integrator coefficient ki 1 Note that kp 0 because the wavemeter mea surement fluctuates within a few MHz ...

Page 33: ...5 4 Examples 27 Figure 5 4 Time series measurement of the wavelength when PID is en abled at about 8 s The setpoint is changed at around 20 s and again at 48 s ...

Page 34: ...28 Chapter 5 PID locking Figure 5 5 The G gain has been increased to 10 V GHz leading to much faster tracking of changes to the setpoint at each of the steps ...

Page 35: ... 29 Figure 5 6 Fluctuations in the measured laser frequency when locked These fluctuations are at the limit of the measurement of the position of the longest etalon fringes a few MHz in a fringe spacing of 7500 MHz ...

Page 36: ...30 Chapter 5 PID locking ...

Page 37: ...ry standard 2x1 switch modules such as the Thorlabs OSW12 series where the port is selected by a single TTL control signal The rear panel M8 switch connector will provide 5 V and a TTL compatible port selection output see F 1 The FZW must be manually configured to drive these devices using the OPTSW 2x1 command The port can then be changed using the same commands used for the FSW devices and mogfz...

Page 38: ...ibre for connection to the FZW It has indents on the top surface that align with the feet of the FZW so the two can be carried together as a single unit Care should be taken to ensure the output fibre is not accidentally sheared 6 3 1 Operation The FSW4 and FSW8 contain a MEMS micro electro mechanical sys tem mirror module that optically couples one of the 4 or 8 input fibres to a single output fi...

Page 39: ...for a different wavelength band There are four optical bands numbered from 0 to 3 Bands 0 1 and 2 are factory optimised using lasers in the blue 400 nm red 600 nm and infra red 1100 nm The normal configuration is as shown in the table below Band 3 can Band Wavelength Range 0 400 nm 400 600 nm 1 600 nm 500 900 nm 2 1100 nm 800 1100 nm 3 Selected be configured on a port by port basis using the value...

Page 40: ... dband command The insertion loss is wavelength dependent varying from 2 or 3 dB for band 1 and wavelengths around 600 to 700 nm to 10 or 15 dB at 400 or 1100 nm even with the optical band optimisation 6 3 3 mogfsw optimiser mogfsw is a tool for minimising insertion losses through the FSW for any specific wavelength For example to reduce insertion losses at 852 nm the laser can be fibre coupled to...

Page 41: ...6 3 MOGLabs FSW fibre switches 35 Figure 6 3 mogfsw allows adjustment of the MEMS mirrors to optimise throughput for a given wavelength for each fibre input port ...

Page 42: ...zw is replaced with a Switch button that opens a new dialogue for monitoring and con trolling the switch channels window shows the wavelength measurement exposure and optical band setting for all channels simultaneously Each port can be con figured for example to select the optical band or to control the PID parameters The figure below Figure 6 5 shows the Switch tool for a 4 port switch Port name...

Page 43: ...al band and PID parameters for each any dark ports otherwise the auto expose algorithm can cause long delays whenever a dark port is selected Exposure The exposure time is displayed The value can be manually adjusted if Auto expose is unchecked The exposure time will be automati cally reduced to less than the dwell time if auto stepping ...

Page 44: ...apter 5 for more details on PID control PID on Allows convenient enable disable of PID feedback for the associated channel The output voltage will be shown in the box above with colour coded background to indicate saturation The colour will be green when the output is near the zero point offset and will become more red as the output voltage approaches either the minimum or the maximum voltage as s...

Page 45: ...he physical switch time and the time to communicate with the optical module For the FSW switches the delay value is typically 8 to 10 ms If set too short the measurements will appear to be unstable Dwell The time to measure each port before stepping to the next Should be set longer than the switch delay and shorter than the maximum exposure time of the port with longest exposure In principle the F...

Page 46: ...hat when PID setup is pressed for a given port the switch will select that port and stop auto stepping to provide the best response times for adjusting the PID parameters The time series window is very useful to monitor the wave length while configuring the PID locking parameters provided auto stepping is not enabled 4 When all ports lasers are locking individually with PID feed back off for each ...

Page 47: ... etalons 4 Smallest etalon FSR 7 5 GHz Electronics DC jack power input 5 V Rev 1 3 or 9 24 V Rev4 as labelled on device Power usage 3 W Display Integrated colour LCD screen Analogue output 16 bit DAC output 2 5 V range 12 bit on Rev 1 3 serial A02xxx 1 Absolute accuracy as measured in a temperature stabilised laboratory envi ronment using a spectrally narrow laser coupled into single mode fibre 2 ...

Page 48: ...Integrated web server Language bindings python MATLAB LabVIEW Mechanical Dimensions W H D 146 120 81 mm Weight 1 5 kg Optical switch Wavelegth range 400 nm to 1120 nm Lifetime 20 billion cycles Connectors3 FC APC input and output Switching speed 5 ms typ 10 ms max Insertion loss4 2 0 dB Return loss 50 dB min 55 dB typ Max optical power 100 mW without damage Dimensions W D H 146 120 33 mm 3 Singlem...

Page 49: ...50 1050 1150 Wavelength nm Quantum Efficiency Figure A 1 Typical detector responsivity Power µW 522 nm 780 nm 1095 nm 0 1 120 580 1 80 40 10 0 8 5 120 100 0 3 0 8 14 200 0 4 2 300 0 2 0 8 Table A 3 Exposure time in milliseconds for different wavelengths ...

Page 50: ...44 Appendix A Specifications ...

Page 51: ...Ensure the serial number matches the device 2 Press the Select button to choose a firmware package to use as downloaded from the MOGLabs website 3 The package is compared against the currently running version to determine which upgrades are required Figure B 2 Up to date components are shown in green upgrades are shown in yellow downgrades in purple and conflicts in red 4 Click on Update all to in...

Page 52: ...t firmware versions 2 Click the Select button 3 to open a firmware package for upload Figure B 2 The firmware update application with a loaded package The versions running on the device are compared against the selected package in this instance showing that an update is available for the IAP yellow and the other components are up to date green ...

Page 53: ...the most recent version of the manual available at http www moglabs com Some commands accept values with units The following units are recognised for returning measurements or defining setpoints nmv vac Wavelength in vacuum in nanometers nma air Wavelength in air in nanometers as measured within the interferom eter May differ from expected standard temperature and pressure STP value due to environ...

Page 54: ...S UNITS units Set the default units for measurement readback as well as the units used by the integrated LCD display SAT MEAS SAT Returns the measurement saturation which is a number in the range 0 100 that measures the optical power reaching the detector Typ ically the saturation should be in the range 50 90 to ensure enough light for rapid measurement but with a substantial margin before oversat...

Page 55: ...g RESET or FACTORY will revert the calibration to the factory provided values IMG MEAS IMG etalon Return interference pattern for specified etalon etalon is 0 to 3 where 3 is the longest etalon usually 7 5 GHz free spectral range The pattern is 512 bytes unsigned integers C 4 Camera When used with an optical switch the following camera settings apply to the currently selected port AUTO CAM AUTO va...

Page 56: ...h the fibre input ports If dwell is not given returns the current dwell time Use zero for dwell to disable auto stepping The dwell time must be greater than the optical switching time see LAG below LAG OPTSW LAG lag Query or set the switching time that is the time to wait after switch ing before measuring wavelengths The time is typically 8 to 10 ms which includes the optical module switching time...

Page 57: ... to that required for older 4x1 versions of the FSW BAND OPTSW BAND int Returns the current optical band 0 to 3 see section 6 3 2 To change the band provide an integer 0 to 3 argument for example OPTSW BAND 3 The selected band applies to all ports Note that the MEMS mirror positions will not change to the new values until the input port is selected with an OPTSW set command DBAND OPTSW DBAND int R...

Page 58: ...LE PID DISABLE Deactivate the PID controller setting the output voltage to the value specified by the OFFSET command see below STATUS PID STATUS Returns the current status of the PID controller SETPOINT PID SET val Set query the PID controller setpoint frequency in THz If val is uses the most recent measurement as the setpoint GAIN PID GAIN val Set query the overall gain used for the PID controlle...

Page 59: ... ing purposes WRITE PID WRITE val Sets output to val if in hex format e g 0x1234 val is 16 bit scaled to 2 5 V DAC 0 will set 2 5 V DAC 0x7fff will set 0 V and DAC 0xffff will set 2 5 V Sets output to offset see above plus val if val is a floating point number DAC DAC val Set output voltage val is 16 bit scaled to 2 5 V DAC 0 will set 2 5 V DAC 0x7fff will set 0 V and DAC 0xffff will set 2 5 V ...

Page 60: ...54 Appendix C Command language ...

Page 61: ...posure time or increase optical power at the input Multi mode Typically occurs if the input light includes several frequencies for example a broad linewidth laser or a laser oscillating on two distinct longitudinal cavity modes The FZW is unable to clearly determine the phase of the interference fringes that is where the peaks occur Internal error Indicates a bug in the software Please contact MOG...

Page 62: ...56 Appendix D Errors and troubleshooting ...

Page 63: ... strongly recommended that all software should wait for this response and check for success before continuing The python and LabVIEW bindings provided take care of buffering and error checking automatically The MOGLabs Commander application mogcmd is available as part of the mogfzw package and provides a convenient interface for send ing commands and receiving responses Figure E 1 E 2 TCP IP The F...

Page 64: ... settings are stored in the non volatile memory of the unit and will be recalled in future 1 From the main menu open Options Ethernet Settings 2 Select Static IP and use the buttons to set the IP address of the device as required 3 Select Gateway and set the gateway address as required 4 Select DHCP and set to OFF 5 Select Restart ethernet and press the OK button 6 The new IP address will be displ...

Page 65: ...ist of devices including Ports Figure E 2 Figure E 2 Screenshot of Device Manager showing that the FZW can be communicated with using COM4 The port number might change when plugging into a different USB port or after applying a firmware update The device can be identified as a COM port with the following name STMicroelectronics Virtual COM Port COMxx where xx is a number typically between 4 and 15...

Page 66: ...re the wavemeter is disconnected from the computer 2 Run the 32 bit or 64 bit USB driver setup program from the package as appropriate for your computer system note that all modern computers are 64 bit 3 Reconnect the wavemeter using the USB cable The device driver will be activated which may take up to a minute 4 The device should be installed as an Virtual COM Port as described above 5 Run the m...

Page 67: ...F Dimensions and PCB 83 120 146 32 9 30V PID TRIG FSW Figure F 1 FZW chassis dimensions 61 ...

Page 68: ...62 Appendix F Dimensions and PCB 146 33 37 120 18 Figure F 2 FSW fibre switch dimensions ...

Page 69: ...R101 F1 LED1 R100 Y1 R96 R93 R94 R95 P7 USB R87 R88 R89 R83 R79 R84 R85 R86 R72 C114 R64 R61 R53 R52 P3 TRIG C101 C102 C103 C107 C105 C89 C91 C93 C94 C95 C96 C99 U15 C87 C86 P10 SPI serial P9 DISPLAY SW2 Power C135 C66 C140 P8 DC 9 36V C131 R99 L1 Y2 R91 C117 C121 C116 C119 R76 R67 R66 U19 R63 P4 PID P1 SENSOR C106 C104 C88 C90 C92 C97 C98 C100 R46 C118 R97 C122 C123 P5 Ethernet R56 R59 R58 R60 R9...

Page 70: ...ata 5 0 V Figure F 4 Fibre switch connectors External M8 and P2 on main PCB type JST type B5B PH SM4 TB LF SN Use Data as TTL control signal for simple 2x1 switches Pin Description 1 0 V 2 Clock 3 Ready 4 NSS 5 MISO 6 MOSI 7 0 V 8 5 V 9 0 V 10 24 V Figure F 5 P10 connector on main PCB for OEM serial communications ...

Page 71: ......

Page 72: ...Laboratories Pty Ltd 49 University St Carlton VIC 3053 Australia Tel 61 3 9939 0677 info moglabs com 2017 2022 Product specifications and descriptions in this doc ument are subject to change without notice ...

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