Realization of ultralow power phase locking by optimizing Q factor of resonant photodetector

We design and construct a resonant photodetector (RPD) with a Q factor of 320.83 at the resonant frequency of 38.5 MHz on the basis of a theoretical analysis. Compared with the existing RPD under the same conditions, the signal-to-noise-ratio of the error signal is increased by 15 dB and the minimum operation power is reduced from -55 dBm to -70 dBm. By comparing the standard deviations of the stability curves, we confirm that the RPD has a dramatic improvement on ultralow power extraction. In virtue of the RPD, we have completed the demonstration of channel multiplexing quantum communication.