Yesterday we first locked the OPO, and we also got the error signal. Let's first compare the transmission power and error signal in reality and simulation(for p-pol).

The simulation result is attached as figure one. The measurement result is attached as figure two.

Since the transmitted power is only roughly a factor of 2.5 lower than simulation. I guess the small error signal is because of the lower gain of PD than we expected.

After get the error signal, we used SR560 to give a low pass filter and achieved lock(can last for several tens of minutes). However, we observed some oscillation which is probably caused by the noise of SR560. I measured the noise spectrum of the error signal. It is in the attached figure 3 and 4. We can see from that the peaks are the harmonic of electrical noise. 

We also measured the opto-mechanical TF. If you are interested in that, please have a look in our wiki page.

The maximization of phase is also done. The procedure is attached in figure 2, 5, 6 and 7. The shape of error signal is quite similar with the simulation. I saved the new set-up of dds2 and the name is today's date.(name: 20181010-dds2, see attached figure 8)

We also found that the amplification factor of the board made by Pier can be increased. See attached figure 9, the magnitude now is 12dBm. However, the maximum we can give is 26dBm(according to the datasheet from Qubig). Since we don't have a large enough error signal, this is also a method we can consider to increase it.