High-precision digital optical phase locking for 10−12 W order weak light for a spaceborne gravitational wave interferometer

Abstract

We developed a digital optical phase-locking loop (DOPLL) for weak light phase locking in spaceborne gravitational wave interferometers (SGWIs). Using the system, we successfully locked the phase of the slave laser to the master laser with the power of only several picowatts, much smaller than the LISA requirement (100 pW). The system does not introduce steady-state errors, and the Bode diagram shows its stability. The out-loop phase noise floor (2.3×10−4 and 5.2×10−4rad/Hz1/2) is very close to the shot noise limit. The Allan standard deviation of the heterodyne signal reaches 3.1×10−17 at 1000 s. With the previous automatic locking program designed by other researchers, the results demonstrate that DOPLLs have bright application prospects and can be applied in the transducer of the SGWI.