Marc, Michael

I wanted to check some of the multiplexer output diagnostics for the PLLs but the BEAT signal (the electrical signal from the fiber PD) had disappeared. We roughly checked the coupling into the CC fiber PD using the power meter and it seems reasonable (ML 4.34 mW, CC 0.64 mW, 1.05 mW out). The fiber PD electrical output have a large DC offset. I noticed that the PPol signal was oscillating at 45 kHz which I thought was a bit strange.

I eventually plugged the CC BEAT signal into the spectrum analyser with a wide setting, and noticed that the large peak corresponding to what was at the level of the previous measured CC BEAT (-11 dBm) had drifted quite far away from its usual frequency setting and the PPol BEAT peak was sitting at the previously mentioned 45 kHz. Both aux laser temperatures were quite far from the values listed in the wiki, so I readjusted them to the proper values and saw the good BEAT signals (CC -11 dBm, PPol -7 dBm).

However, the CC PLL lock is still unstable. Using MUXOUT on the CC PLL board, I could see that the digital lock detection was not particularly great. Digital lock detection outputs 1 when the phase delay between 3 cycles is less than 15 ns, and 0 when not. I noticed the output was not continuously 1 (i.e. has a lot of phase noise). It remained locked for about 4-5 minutes. I still need to figure out what the other diagnostic functions do.