Demonstration of a silicon photonics integrated 1645 nm stabilized seed laser for methane and water vapor remote sensing lidar

The frequency-stabilized laser (FSL) is a vital component of differential absorption lidar (DIAL) and can satisfy the requirements for high-precision gas species concentration detection. China's next-generation spaceborne integrated-path differential absorption (IPDA) lidar aims to perform high-precision, multi-species detection of methane and water vapor column concentrations in the atmosphere. The seed laser system requires long-term frequency stability, low power consumption, and a compact size. Here, a 1645 nm triple-wavelength FSL based on silicon-on-insulator (SOI) photonics integrated circuits (PIC) is proposed; its advantages in size, weight, and power consumption (SWaP) are also demonstrated. Over a measurement period of up to 24 hours, the FSL's frequency standard deviation is better than 400 kHz. The peak-to-peak frequency drift is down to 4 MHz under 9 hours of recording. An optical phase-locked loop (OPLL), capable of a frequency difference of up to 28.23 GHz, was constructed, ensuring the long-term stability of the seed laser even under large frequency differences. The FSL is qualified to generate three seed laser pulses and inject them into the 1645-822 nm optical parametric oscillator (OPO). Regarding the 10 MHz wavelength drift requirement of IDPA lidar, the FSL has an environmental temperature tolerance of over 1°C. Furthermore, in the analysis of the PDH frequency stabilization loop based on silicon photonic chips, we have proposed a mathematical analysis for the nonlinear phase modulation.