I measured RIN of the two paths yesterday through taking spectrum of transmission PDs and measured cross-correlation with the Beatnote.

Measurement conditions:

• Beatnote frequency was not temperature controlled and was arounf 127 MHz slowly increasing.
• Note, this is near the edge of the DC-125 MHz wideband RF detector used for BN measurement.\
• PLL Actuation slope was 5 kHz/V
• Cross-correlation was measured as a FFT group measurement by SR785 using Cross Spec measurement.
• Averaging was on and set to 50 with Linear averaging.

Conclusions:

From the plots attached, it is clear that RIN of both paths have a peak near 3 kHz but the south path has excessive RIN in comparision to North parth and has much more coherence with BN. I'm looking into possible RF AM in south path.

Edit Wed Jan 16 14:08:03 2019 :

I forgot to convert the noise spectrum measured to laser power spectrum earlier. I am also realizing now that I should have measured the transmitted power to get the RIN. So this measurement only provides Intenisty (or Power) noise of transmitted lasers. I'm attaching the fixed plot now.