Demonstration of Photonic Integrated Circuit Seed Laser System: Toward Space-Based Water Vapor and Methane Differential Absorption Lidar

Differential absorption lidar (DIAL) systems are used for accurate vertical profiling and high precision columnar retrievals of molecular components of the atmosphere. Future space-based DIAL systems will enable global monitoring of species crucial to understanding weather and climate systems such as water vapor and methane. DIAL systems require dynamic, high-stability seed laser sources to provide accurate, sensitive measurements by tuning on and off molecular absorption lines. The NASA Langley Research Center is developing a seed laser system for DIAL detection of water vapor and methane based on a core photonic integrated circuit (PIC) subsystem including dual tunable lasers, amplifiers, modulators, photodiodes, and a passive splitter/combiner network on-chip. In this Article, we assemble a breadboard prototype of the seed laser source composed of a first generation PIC, a methane cell, a passive fiber network, and electronic controllers. The seed laser prototype's performance is demonstrated in terms of PIC laser and modulator performance, online locking accuracy to a methane cell, rapid offset-locking accuracy for the DIAL measurement, and long-term stability. This initial demonstration achieves key performance metrics necessary for space-based DIAL measurements of water vapor and methane, providing a clear path toward a future space-grade system.