Frequency-modulated diode laser frequency combs at 2 μm 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 μm has been scarce. Here, we present a frequency-modulated OFC operating around 2060 nm of wavelength exploiting the inherent gain nonlinearity of single-section GaSb-based quantum well diode lasers. A 2 mm long device operating as a self-starting comb outputs 50 mW of optical power over more than 10 nm of bandwidth while consuming <1 W of electrical power. Using the shifted-wave interference Fourier transform spectroscopy technique, we characterize the generated frequency-modulated waveform and demonstrate a linearly chirped intermodal phase relationship among the entire emission optical bandwidth. Furthermore, by compensating for the linear chirp using a single-mode optical fiber with opposite dispersion, 6 ps long optical pulses are generated. The frequency stability of the devices with ∼19.3 GHz repetition rates allows us to perform mode-resolved free-running dual-comb spectroscopy. All rights reserved.