Specifications

4.2 Scanning 17
Frequency (GHz)
Relative Gain
1
0
0
100-100-200 200
Figure 4.2: Combinedgainforanexternalcavitydiodelaser,includingthe
internalandexternalmodes,thediodelasergain,andthefilterabsorption.
The predominantfeatureisthefrequencyselectivityof thefilter, andthe
smallerpeaksaretheexternalcavitymodes(seeFig.1.3).Asmallrelative
shift of the external cavity mode relative to thefilter frequency will cause
thelasertojumptoanotherexternalcavitymodewherethenetgainis
higher.
“automatically” adjusted asthe laser frequency is changed,using a
“feed-forward”orcurrentbiaswhichchangesasthepiezovoltage
ischanged. Feed-forwardcurrentbiasadjustmentisafeatureof
MOGLabs DLCcontrollers.Adjustment isstraightforward.The laser
frequency isscanned (witha downwardramp voltage tothe piezo),
andthecurrentbiascontrolisadjustedsothatthecurrentisalso
rampingdownward, untilthemaximum mode-hop-freescan range is
observed. Smallchangestothe injectioncurrentoptimisethe scan
range near the nominal centre frequency.