4. Troubleshooting
4.1 Scanning adjustment
Achievingawidecontinuousmode-hopfreewavelengthscanrequirescare-
fuloptimisationofthecontrolparameters,includinglaserdiodecurrent,
piezooffset,andfeed-forwardcurrentbias(see§4.1.1). Thelaserhas
beencarefullytunedtothewavelengthandscanrangespecifiedinthe
lasertestreport.Theinstructionsbelowdescribehowtoachievethemax-
imum mode-hop free range (MHFR).
Thefirststepistoconfirmthatthelaserisindeedscanning,forexam-
ple with a wavemeter such as the MOGLabs Fizeau wavemeter (FZW),
MOGLabs economical wavemeter (MWM), or a Fabry-Perot cavity.
1. SlowlyincreaseSPAN whilemonitoringthefrequencychangewith
a wavemeter.
2. Ifthereisnochangeinscanrange,thendisablefeed-forwardcurrent
biasusingDIPswitch4 in theDLC.Ifthereisnoevidencethatthe
laserisscanningwithbiasdisabled,thenthepiezohasfailed;please
contact MOGLabs for assistance.
3. If thelasersucccessfullyscanswith biasdisabled,nowenable feed-
forward current bias usingDIPswitch 4 in the DLC.Slowly increase
SPAN,andusesmalladjustmentsofCURRENTand piezooffsetFRE-
QUENCYto suppress any mode-hops observed.
4. IncreaseSPAN tothemaximumbeforemode-hopsareevidentand
compareDLC CHANA Freq andCHANB Current tothevalueslisted
intheMOGLabslasertestreportprovidedwithyourlaser. Ifthe
peak-to-peakvoltagedifferencesaremorethanabout10%,thenBIAS
adjustment is recommended.
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