Wavelength Tunable 100 MHz Gain Switched Optical Frequency Comb for Cavity-Enhanced Absorption Spectroscopy

A wavelength tunable (35 nm), low repetition rate (100 MHz) optical frequency comb generated by gain switching an externally injected Fabry-Pérot laser using a step-recovery diode is demonstrated. The comb possesses ~1000 comb tones over a ~100 GHz span. It was passively coupled to a medium finesse cavity in off-axis configuration. An ammonia (14NH3) detection limit of ~5.6 ppmv in 20 s was accomplished in static dry air using a Fourier transform spectrometer. The photonically integrable architecture used in this work provides a compact, cost-efficient, high-frequency resolution and wavelength tunable low repetition rate OFC, capable of sensing multiple trace gases.