I roughly calculated power of BAB transmission from filter cavity. When the injection of BAB is 200uW, transmission power at PD is 1.2uW. If we use parametric amplification, we can increase it by a factor of 20. Here is the assumption.

 

BAB injection: 200uW

Injection loss: 10%

Transmission of filter cavity: 1%

Transmission of IR line filter in End bench: 70%

BAB transmission at PD: 1.2uW