Partecipants: Marco, Eleonora

We repeat the same work reported in the entry 838 but this time we reverted the lasers configuration: AUX1 is the Slave laser and AUX2 is the Master laser of the OPLL. 

The circuit scheme is the same used for the other measurement, the selected loop filter was the same of the Config1: C1=680nF R1=27Ω and C2=100nF. The charge pump current was set to 3.75mA and the frequency offset was set to 20MHz.

Picture 'PLL_20MHz.jpg' shows the 20MHz beat note peak once locked. We can see the same structures of the previous configuration.

The phase noise was measured again with the demodulation technique. The mixer calibration factor is measured at 100Hz and is again Vpp=98mV.

The measured phase noise is shown in picture 'pll20mhzpn.pdf' the blue line represents the phase noise of the pll with AUX2 slave laser and the red line represents the phase noise with AUX1 as slave laser.

The rms phase noise between 120 Hz and 102.4kHz is equal to 10.04 mrad.

We try to increase the CP gain in order to decrease the phase noise but the first laser PZT resonance was excited (see fig 'pll20mhzaux2res.jpg'). A notch filter centered at f=160kHz will be added in series to the loop filter.