I checked PDH error signal (green line) with low-pass filter.
Though the time resolution is higher than before, still the error signal is spike-ish structure.
This may be due to too high finesse of silicon cavity.
At this moment, I did not use frequency scan by laser PZT, but temperature fluctuation of laser induced frequency fluctuation.
Thus I could see error signal without scanning laser frequency.

It needs temp. control loop for stable lock.
Anyway, I will consider cotrol loops for TEM00 lock.