MOGlabs FZW600 User manual
Fizeau Wavemeter
FZW600
Version0.1.2,Rev2hardware
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Contents
Getting started iii
1 Introduction 1
1.1 Howitworks....................... 1
1.2 Features.......................... 2
2 Connections and controls 3
2.1 Frontpanelinterface . . . . . . . . . . . . . . . . . . . 3
2.2 Rearpanelcontrolsandconnections. . . . . . . . . . 6
3 User interface 7
3.1 On-boardUI........................ 7
3.2 WebUI........................... 8
3.3 SoftwareUI........................ 9
4 Operation 15
4.1 Fringeidentificationandoptimisation . . . . . . . . . 15
4.2 Auto-exposurealgorithm. . . . . . . . . . . . . . . . . 18
4.3 Wideandfastmodes . . . . . . . . . . . . . . . . . . . 18
4.4 Pulsedlasermeasurement. . . . . . . . . . . . . . . . 19
4.5 Externallytriggeredmode. . . . . . . . . . . . . . . . 19
4.6 Measurementaveraging . . . . . . . . . . . . . . . . . 20
4.7 PIDcontrol........................ 21
4.8 Calibrationadjustment . . . . . . . . . . . . . . . . . . 22
5 Optical switcher 25
5.1 Overview.......................... 25
5.2 Operation......................... 26
5.3 SoftwareUI........................ 26
i
ii Contents
5.4 SimultaneousPID . . . . . . . . . . . . . . . . . . . . 26
A Specifications 27
B Firmware updates 31
C Command language 33
C.1 Generalfunctions . . . . . . . . . . . . . . . . . . . . . 33
C.2 Displaysettings . . . . . . . . . . . . . . . . . . . . . 34
C.3 Measurementsettings . . . . . . . . . . . . . . . . . . 34
C.4 Camerasettings...................... 35
C.5 Opticalswitch....................... 36
C.6 PIDcontrol........................ 37
D Communications 39
D.1Protocol.......................... 39
D.2TCP/IP........................... 39
D.3USB............................ 41
E Dimensions 43
Getting started
1. Connect to +5 V power viatheUSBportortheDCbarreljack.
When powering with USB, it is important that the host can
supplyupto600mA.Someoldercomputersmaydetectthisas
ashort-circuitandpowerdownthedevice;USB-3.0compliant
hubsarerecommended.
2. Power on usingtherockerswitchontherear.
3. Connect fibre using the supplied fibre patchcord. Typically
this is FC/PC (black) on one end and FC/APC (green) on the
other. TheFC/PC sidemustbeconnectedtotheFZW.
IfthedevicewasorderedwiththeFC/APCoption(asindicated
onthechassis),thesuppliedfiberisFC/APC onbothendsand
eitherendcanbeconnectedtotheFZW input.
Single-modefibresarestronglypreferred,althoughsmall-core
multi-modefibres(upto62.5µm)canbeusedattheexpense
ofreducedaccuracy.1
4. Input light withthesuppliedfree-spacetofibreadapter. Typi-
callytheFZWonlyneedsafewmicrowattstooperate,sohigh
couplingefficiencyisnotrequired. Thesaturation (Figure1)
isameasureofthepowerreachingthedetector
Theauto-exposurealgorithmtunestheexposuretimetomatch
theinputpowerandoptimisethemeasurementrate. Insome
casesitmaybepreferabletosettheexposuretimemanually,
suchaswhenperformingmaintenanceonthesourcelaserand
thelaseroutputpowertendstofluctuaterapidly.
That’sit: withacoupledfiberyoushouldbeabletoreadthewa-
velength within two seconds of power-on. It is recommended to
1Absoluteaccuracyspecificationsareonlyvalidwhenusingsingle-modefibres.
iii
iv Getting started
Figure 1: Both the built-in wavemeter display (left) and host software
(right) provide saturation indicators that measure the optical power rea-
chingthedetector.
periodically inspect the measured interference fringes for correct
structure(§4.1)toensurereliablemeasurement.
TypicallytheFZW willreachthermalequilibriumandfullaccuracy
within15minutesofbeingturnedon. Themostaccurateresultswill
beobtainedinawell-stabilisedlabenvironment. Itisrecommended
thattheFZWnotbeinthermalcontactwithanyotherequipmentto
preventformationofthermalgradients.
Host connection
TherecommendedmodeofoperationisusingtheWindowsTM host
application (chapter 3) which provides a simple interface for con-
trollingdevicefunctionality. Instructionsforconnectingviaethernet
andUSB areprovidedinAppendixD.
1. Introduction
1.1 How it works
TheFZWisahigh-precisiondevicethatmeasureslaserwavelengths
using a set of Fizeau interferometers. A Fizeau interferometer is
formed by two planar surfaces with a small wedge angle between
them,whichgeneratesspatially-varyinginterferencefringesasthe
opticalpathlengthchanges(Fig.1.1). Boththefringespacingand
phase of the resulting interference pattern are related to the wa-
velength of the incident light, so analysing their structure allows
precisedeterminationofthelaserwavelength.
Figure 1.1: CollimatedmonochromaticlaserlightandFizeauetalonscre-
ateinterferencepatternsonanimagingdetector. Thewavelengthiscalcu-
latedbycombiningmeasurementsofthefringesfromfourdifferentetalons.
A rough estimate of the wavelength is obtained directly from the
fringe spacing, to an absolute accuracy of one part in 100. This
initialestimateisthenimprovedbythephaseofthefringepattern.
Multipleetalonswithdifferentfree-spectralranges(FSRs)areused
to refine the wavelength measurement without sacrificing absolute
accuracy. TheMOGLabsFZWusesfoursuchstages,withtheFSRof
thefinaletalon being7.5GHz. Thisenablesthe wavelengthtobe
determinedtoanabsoluteaccuracyofonepartin107.
1
2Chapter 1. Introduction
1.2 Features
The MOGLabs FZW has no moving parts, and very high sensitivity
semiconductor imaging, enabling high measurement speed (up to
350persecond)andmeasurementofpulsedsourceswithonlyafew
microwattsoflight.
Longlifetimeisassuredastherearenomechanicalpartstowearout.
Theetalonsareoptically-contactedfusedsilica,withalowthermal
expansioncoefficient,makingtheinstrumentincrediblyrobust,reli-
able, and stable. High precisionMEMS-based sensors areusedto
make small corrections for environmental variations. Recalibration
isnotrequiredtomaintainthestatedaccuracy;infact,theFZW is
morestablethantheneonlampusedinsomeotherwavemetersas
acalibrationsource.
TheFZW alsointegratesamodern32-bitmicroprocessorandhigh-
resolutioncompactcolourdisplay. Wavelengthcalculationisperfor-
medautomaticallyonthedevicesothatnohostcomputerisrequired.
ItiscompactandcanbepoweredfromUSB orevenarechargeable
battery,soyoucanmoveitaroundyourlabandmeasurewavelength
rightwhereyouareadjustingyourlaser.
Fast ethernet and USB communications combined with a sophisti-
cated software suite enable display on your lab computer or your
smartphone. MultipleFZW devicescanbeeasilyrun fromasingle
computer, and integration with common data acquisition systems
issimpleusingtext-basedcommandsoverstandardprotocols,with
simplebindingstoLabVIEW,MATLAB,andpython provided. PIDfre-
quency feedback locking is also included with every device, also
withoutrequiringahostcomputer.
2. Connections and controls
2.1 Front panel interface
The FZW front panel (Figure 2.1) includes an interactive colour
screenwithpush-buttoninterface,andanumberofstatusindicator
lights. This allows autonomous usage of the wavemeter indepen-
dentlyofacomputer.
Figure 2.1: MOGLabsFZW frontpanellayout.
Thebuttonsarearrangedasa“directionalpad”withup,down,left
and right buttons, and an additional OK button in the centre. In
wavelengthdisplaymode,theup/downbuttonschangethedisplay
units, and the left/right buttons swap between different diagnostic
modes(see§3.1). PressingOK opensthemenusystem.
The display includes a sleep mode which reduces the brightness
whennotinuse. Wherethisfeatureisundesirableitcanbedisabled
bysettingthesleeptimetozerointhemenusystem.
3
4Chapter 2. Connections and controls
TheLED indicatorsdisplaythecurrentstateofthedevice,aslisted
inthetablebelow.
Indicator Colour Status
PWR ÊOff Unitispoweredoff
Green Normaloperation
Blue Firmwareupdatemode
ERR ! Off Nomeasurementinprogress
Green Normaloperation
Yellow Measurementerror
Red Criticaldeviceerror
LOCK Off PID/analogoutputdisabled
Green PIDlocked
Yellow PIDengagedbutnotlocked
Red PIDoutputsaturated
Blue Analogoutputerror
2.1.1 Menu system
Themenusystemallowsforinteractivecontrolofthedevicewithout
acomputerinterface(Figure2.2). ItisstartedbypressingtheOK
buttonfromthemeasurementdisplaymode,andexitingbypressing
theleftdirectionalbutton.
Figure 2.2: Primary settings menu, showing measurement options (left)
anddevicesettings(right)whichincludesdisplaysettings.
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