(notes on signal level)
The signal level of the observed peak was -48dBm.
However I was expecting it is like -28dBm with some ideal assumptions.
There may be a 20dB unknown loss which sounds big to me.
The expectation was calculated by using the following simple math.
SIGNAL = A x Z x G_RF x sqrt(P1 / 2) x sqrt (P2 / 2)
where A is the responsibility of the PD and Z is the trans impedance gain. G_RF is a gain of the RF amplifier.
The laser powers of green beams, P1 and P2, are divided by 2 due to a beam splitter.
I was assuming the parameters are like:
A = 0.39 [A/W] (assuming 90% quantum efficiency at 532nm)
Z = 240 [V/A]
P1 = 17 uW (measured by Newport power meter)
P2 = 30 uW (measured by Newport power meter)
G_RF = 23 dB