MOGlabs FZW600 User manual

Fizeau Wavemeter and Fibre Switcher
FZW600, FSW4, FSW8
Version0.3.2: Rev2hardware,firmwarev0.9.3,mogfzwv1.4.1

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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 DeviceUI......................... 7
3.2 WebUI........................... 8
3.3 SoftwareUI........................ 9
4 Operation 13
4.1 Fringeidentificationandoptimisation . . . . . . . . . 13
4.2 Auto-exposurealgorithm. . . . . . . . . . . . . . . . . 16
4.3 Fastmode......................... 16
4.4 Pulsedlasermeasurement. . . . . . . . . . . . . . . . 16
4.5 Externallytriggeredmode. . . . . . . . . . . . . . . . 17
4.6 Measurementaveraging . . . . . . . . . . . . . . . . . 17
4.7 Calibrationadjustment . . . . . . . . . . . . . . . . . . 18
5 PID locking 21
5.1 UsingwithMOGLabsDLC lasercontroller . . . . . . 22
5.2 PIDparameters...................... 22
5.3 Integratorwindup. . . . . . . . . . . . . . . . . . . . . 24
5.4 Examples.......................... 25
i

ii Contents
6 Optical switch 31
6.1 Overview.......................... 31
6.2 Operation......................... 32
6.3 Opticalbands....................... 32
6.4 mogfzwswitchUI . . . . . . . . . . . . . . . . . . . . . 34
A Specifications 37
B Firmware updates 41
C Command language 43
C.1 Generalfunctions . . . . . . . . . . . . . . . . . . . . . 43
C.2 Displaysettings . . . . . . . . . . . . . . . . . . . . . 44
C.3 Measurementsettings . . . . . . . . . . . . . . . . . . 44
C.4 Camerasettings...................... 45
C.5 Opticalswitch....................... 46
C.6 ControlvoltageoutandPID . . . . . . . . . . . . . . 47
D Communications 49
D.1 Protocol.......................... 49
D.2 TCP/IP........................... 49
D.3 USB............................ 51
E Dimensions and PCB 53
E.1 Internalconnectors . . . . . . . . . . . . . . . . . . . . 56

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
thisisFC/APC (green) atbothends,butcanbeFC/PC (black)
toFC/APC (green); inthatcase,theFC/PC blacksidemustbe
connectedtotheFZW.
Single-modefibresarestronglypreferred,althoughsmall-core
multi-modefibres(upto62.5µm)canbeusedattheexpense
ofreducedaccuracy.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.
ElectricallyconnecttheFSW andFZW usingthesuppliedM8
cable. Connectyourlightsourceviafibretooneofthe4or8
inputportsontheFSW.
5. Input light withthesuppliedfree-spacetofibreadapter. Typ-
icallytheFZWonlyneedsafewmicrowattstooperate,sohigh
couplingefficiencyisnotrequired. Thesaturation (Figure1)
isameasureofthepowerreachingthedetector
Theauto-exposurealgorithmtunestheexposuretimeandsen-
sorgaintomatchtheinputpowerandoptimisethemeasure-
mentrate. Manualsettingsmaybepreferable, forexampleif
thelaserpowerisrapidlyfluctuating.
1Absoluteaccuracyspecificationsareonlyvalidwhenusingsingle-modefibres.
iii

iv Getting started
Figure 1: Both the built-in wavemeter display (left) and host software
(right)providesaturationindicatorsthatmeasuretheopticalpowerreach-
ingthedetector.
That’sit: withacoupledfibreyoushouldbeabletoreadthewave-
lengthwithintwosecondsofpower-on. Itisrecommendedtoperiod-
icallyinspectthemeasuredinterferencefringesforcorrectstructure
(§4.1)toensurereliablemeasurement.
TypicallytheFZW willreach thermal equilibrium and fullaccuracy
within15minutesofbeingturnedon. Themostaccurateresultswill
beobtainedinawell-stabilisedlabenvironment. Itisrecommended
thattheFZW notbeinthermalcontactwithanyotherequipmentto
preventformationofthermalgradients.
Host connection
The recommended mode of operation is using the Windows™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-varying interferencefringesasthe
opticalpathlengthchanges(Fig.1.1). Boththefringespacingand
phaseoftheresultinginterferencepatternarerelatedtothewave-
lengthoftheincidentlight,soanalysingtheirstructureallowspre-
cisedeterminationofthelaserwavelength.
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. TheMOGLabsFZW usesfoursuchstages,withtheFSR of
the final etalon being 7.5GHz. This enables the wavelength to be
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 precision MEMS-based sensors are used to
make small corrections for environmental variations. Recalibration
is notrequiredtomaintainthestatedaccuracy; in fact, theFZW is
morestablethantheneonlampusedinsomeotherwavemetersas
acalibrationsource.
TheFZW alsointegratesamodern32-bitmicroprocessorandhigh-
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
rechargeablebattery,soyoucanmoveitaroundyourlabandmea-
surewavelengthrightwhereyouareadjustingyourlaser.
Fast ethernet and USB communications combined with a sophisti-
cated software suite enable display on your lab computer or your
smartphone. Multiple FZW devices can beeasilyrun from a single
computer, and integration with common data acquisition systems
issimpleusingtext-based commands over standard protocols, 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.
Thebuttonsarearrangedwithup,down,leftandrightbuttons,and
anadditionalOK buttoninthecentre. Inwavelengthdisplaymode,
theup/downbuttonschangethedisplayunits,andtheleft/rightbut-
tonsswapbetweendifferent diagnosticmodes(see§3.1). Pressing
OK 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/analogueoutputdisabled
Green PIDlocked
Yellow PIDengagedbutnotlocked
Red PIDoutputsaturated
Blue Analogueoutputerror
2.1.1 Menu system
Themenusystemallowsforinteractivecontrolofthedevicewithout
acomputerinterface(Figure2.2). Itisstartedby pressingtheOK
buttonfromthemeasurementdisplaymode,andexitingbypressing
theleftdirectionalbutton.
Figure 2.2: Primary settings menu, showing measurement options (left)
anddevicesettings(right)whichincludesdisplaysettings.