Frequency-modulated diode laser frequency combs at 2 m wavelength

Chip-scale electrically pumped optical frequency combs (OFCs) are expected to play a fundamental role in applications ranging from telecommunications to optical sensing. To date, however, the availability of such sources around 2 um was scarce. Here, we present a frequency modulated (FM) OFC operating around 2060 nm of wavelength exploiting the inherent gain nonlinearity of single-section GaSb quantum well diode lasers. A 2 mm long device operating as a self-starting comb outputs 50 mW of optical power over 10 nm of bandwidth while consuming <1 W of electrical power. Using the Shifted Wave Interference Fourier Transform Spectroscopy (SWIFTS) technique, we characterize the generated frequency-modulated waveform, and demonstrate a linearly chirped phase relationship among the entire emission optical bandwidth. Furthermore, by compensating for the linear chirp using a single mode optical fiber with opposite dispersion, 10 ps-long optical pulses are generated. The high frequency stability of the devices with 19.3~GHz repetition rates allows us to perform mode-resolved free-running dual-comb spectroscopy.