Single-wavelength InGaAs/AlAs(Sb) quantum cascade lasers

Recently, significant progress has been made in the development of short-wavelength quantum-cascade lasers (QCLs) emitting in the 3-4 μm wavelength range, where many molecular species of interest have their strongest rotational-vibrational absorption bands. A laser designed for gas sensing applications must have a narrow spectral width in order to differentiate between the fine features of the unique absorption fingerprint of the gas. Using a distributed-feedback (DFB) design, single-wavelength operation is achieved with a first order lateral grating etched in the same step as the laser cavity (Fig. 1) Driven pulsed at a temperature of 303 K, emission was at a wavelength of 3.35 μm (Fig. 2) with a side mode suppression ratio (SMSR) of 24 dB. In the discrete-mode (DM) design index perturbations were introduced in to the laser cavity. The features modify the Fabry-Pérot (FP) cavity loss spectrum such that lasing is in a single FP mode. Driven pulsed at a temperature of 300 K, emission was at wavelength of 3.31 μm (Fig.3) with a SMSR of 25 dB.