[Aritomi, Yuhang, Michael]

We measured CCFC FDS with fixed homodyne angle for 3 hours with 30 minutes interval (figure 1). We fixed OPO temperature to 7.163kOhm and p pol PLL frequency to 200MHz.

According to the least square fitting, the detuning changed by 9Hz in 3 hours even with fixed homodyne angle.

We measured shot noise before/after all the FDS measurement (figure 2). The shot noise is the same in 3 hours.

We also measured nonlinear gain after each FDS measurement. The nonlinear gain changed from 4.6 to 4.2 in 3 hours, which corresponds to generated squeezing of 10.3 dB to 9.8 dB. 

Regarding the nonlinear gain measurement, we divided the BAB transmission with 20mW green by that without green. For BAB transmission with 20mW green, we fixed p pol PLL frequency to 200MHz and locked OPO and measured the maximum value of BAB transmission by scanning CC1 with 20mW green. The reason why we fixed the p pol PLL frequency is that it was fixed during the FDS measurement. For BAB transmission without green, we scanned OPO and measured the peak value of BAB transmission.

There are two mechanisms which change the BAB maximum with 20mW green. One is the nonlinear gain change and another is optimal p pol PLL frequency change (in other words, s&p overlap inside OPO or BAB detuning inside OPO). In the nonlinear gain measurement above, s&p do not always overlap inside OPO with 20mW green (BAB can be detuned inside OPO), while they overlap without green. This means that in this method, the measured nonlinear gain change is due to both of the real nonlinear gain change and optimal p pol PLL frequency change.

To measure the real nonlinear gain change, we need to optimize p pol PLL frequency every time we measure the nonlinear gain to make sure s&p overlap with 20mW green.

sqz_dB = 10;                      % generated squeezing (dB)

L_rt = 120e-6;                    % FC losses

L = 0.52;                         % propagation losses   

A0 = 0.06;                        % Squeezer/filter cavity mode mismatch

C0 = 0.02;                        % Squeezer/local oscillator mode mismatch

ERR_L =   1.5e-12;                % Lock accuracy (m)

ERR_csi = 30e-3;                  % Phase noise (rad)