I checked that the optical gain in PMC loop increases as the power in the sideband increases. The result is 10.7 dB/V.
This measurement is for checking how much gain (in optical path) will we get from changing power in the side bands.
The excitation is sent to EXT DC channel on PMC. Reference signal is at HV mon, response is picked up at Mix mon.
This TF includes PZT and OPT paths, PZT TF should remain the same independent from the side band power.
I vary the RF voltage, and adjust the gain slider for maximum stability. The gain setup should not matter
in the TF part we are measuring as long as the loop is stable.
I measured the gain at 3 different frequencies, 290.8 Hz, 1.035 kHz, 5.09 kHz where the TF look reasonable and smooth.
(The loop UGF is ~ 500-900 Hz, Thus the data at 1k and 5 kHz are nicer than that of 290 Hz)
the slopes from each fit are
The results are fairly linear in our region (RF between 4.8 to 5.9 V). The gain slider for this voltage range is between 13 - 20 dB.
At higher RF voltage, PMC_RCTRANSPD starts to drop significantly.
At lower RF voltage, the gain is too low.
This means we can increase the gain in OPT TF up to 10 dB by adjusting RF voltage (increase side band power)