Chien-Ming, Yu-Hang, and Aritomi
We replace the flipping mirror of BAB and CC to a 2" BS today.
As for the p-pol PLL, Yu-hang saw a 0.1Hz slow fluctuation signal at the output of the monitor mixer. The input to the mixer were 252 MHz laser beat frequency and 252MHz DDS channel 2 output. Today, we try to figure it out but fail to see the fluctuation at 252MHz but at 150MHz (We adjust the beat frequency to close to 150MHz).
We use the spectrum analyzer to check the output of the DDS directly. We see a drop in DDS amplitude after 200MHz as shown. The drop after 240MHz is serious and there is another peak appearing. However, we assume that the DDS should be able to provide up to 500MHz.
We feel that the 0.1Hz slow fluctuation may be due to the phase (or frequency) difference from DDS after frequency division. (For locking to 252MHz, the PLL needs to be divided by 3).
The characterization of the DDS output was done long time ago. You can find the graph here.
As clear from the schematics there is a high order low pass filter with corner frequency around 200MHz, therefore the cut is expected.