12-ns Frequency Chirped Pulse for Self-Calibrated Gas Sensing

We present the generation of 12.1 ns frequency chirped pulses from a distributed feedback laser diode via injection current modulation and demonstrate its application to absorption-based methane sensing at 1650.9 nm. The chirp spectral distribution is found to be significantly impacted by the transient dynamics of these short pulses. A simplified, two-part model is used to evaluate the chirp property, suggesting spectral mixing and oscillation. The chirp enables intra-pulse self-calibrated gas sensing by taking the amplitude ratio between the absorption peak and a reference, which is demonstrated for methane concentrations from 0 to 22.6% with a detection limit of 25 ppm. It also provides resistance to power fluctuation from various sources. These short pulses offer high spatial and temporal resolution and can potentially enable reflection-based, highly multiplexed gas sensing systems.