Self‐Detecting Mid‐Infrared Dual‐Comb Spectroscopy Based on High‐Speed Injection‐Locked Quantum Cascade Lasers

Dual‐comb spectrometer based on quantum cascade lasers (QCLs) is gaining fast development and revolutionizing the precision measurement with high‐frequency and temporal resolutions. In these measurements, high‐bandwidth photodetectors are normally used for signal acquisition and processing, which complicates the measurement system. QCL is well‐known for its picosecond gain‐recovery time with an intrinsic bandwidth of tens of GHz. In this work, a compact self‐detecting dual‐comb spectroscopy (DCS) is demonstrated based on dispersion‐engineered, high‐speed packaged QCLs under coherent injection locking. The laser source is designed and fabricated into a hybrid‐monolithic‐integrated waveguide and epi‐down packaged on a wideband‐designed submount to fully explore the high‐speed feature up to fourth‐order harmonic state with a cutoff frequency of 40 GHz. The effective radio frequency (RF) injection locking diminishes the issue of optical feedback and enables high‐bandwidth self‐detection based on QCLs. Clear and stable multiheterodyne signal corresponding to a spectral range of 68 cm −1 and narrow comb tooth linewidth of ≈10 kHz is observed without using external detector or numerical process. The demonstrated broadband, high‐power, self‐detecting mid‐infrared QCL DCS has a great potential for future applications of molecular sensing and spectroscopy.