On-chip Mach–Zehnder interferometer for 1550 nm laser frequency stabilization

Low-noise stable lasers have broad applications in metrology, spectroscopy, communication, and quantum physics. Here we demonstrate locking a semiconductor laser to an on-chip silicon nitride Mach–Zehnder interferometer (MZI) using the Pound–Drever–Hall (PDH) stabilization technology. After locking, the frequency noise of the laser is suppressed by up to 37 dB, and the relative stability reaches 3 × 10 −10 at a gate time of 1 ms, showing an order of magnitude improvement compared to a free-running operation. In addition, the linewidth of the stabilized laser is 420 kHz at an integration time of 10 ms, narrowed by eight times.