PDH is one method what are other options to achieve stable locking of of DFB-LD to scanning fabry perot etalon with FSR=1.5GHz and 3-dB BW=7.5MHz.
I want to lock DFB-LD to FPE negative transmission slope at half power point by applying negative feedback, Require longer stability (atleast an hour)?
I maximized the signal coupling from DFB-LD into Etalon by observing transmission modes on oscilloscope. At maximum coupling I observed mode jittering , may be due to temperature dependence of cavity length.
What procedures should I adopt to achieve lockinng?
Note: Please see the figure in the attachment
Since the linewidth of your laser is comparable to the linewidth of the etalon you will always observe relatively large jitter/fluctuations in your signal. Temperature drifts are usually slow, and will thus not affect locking. Jitter could also be caused by optical feedback from the FPI, back to the DFB (depending on the isolation of the fiber circulator). Generally it should just be a matter of adjusting the P and I parameters of your servo controller, but if there is optical feedback or the jitter being too high for a stable lock you may want to try locking to a broader lineshape first (lower Finesse FPI, gas absorption line)
for lower noise, also something like a simple dither lock is possible using laser current modulation and a lock-in amplifier if available.
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