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

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.