Earlier measurements of the modulation index were less than optimal because we had too low transmission through the cavity. Contrary to what was believed you actually need to modematch onto the cavity.

Earlier transmitted power was about 8.5uW.

With a 250mm lens we archived 41uW.

Impinging power on the cavity is 1.7mW.

PD TF approx 0.1V / uW.

Carrier power: 4.1V => 41uW

41uW/1.7mW = 2.4 % transmission. Manufacturer clain for peak transmission: 20-30%.

11MHz SB: 28.8mV => m=0.17

55MHz SB:36mV => m=0.19


As you can see on the pic the SNR of the SBs is not too good.