Mid-Infrared Quantum Cascade Laser Frequency Comb Tightly Locked by Near-Infrared Light Modulation

Quantum cascade lasers (QCLs) are frequency comb sources for the mid-infrared (MIR) [1]. They are mainly exploited for dual-comb spectroscopy, but other applications of interest are accurate frequency calibration [2] and synthesis. However, this requires high spectral purity, which demands a fast stabilization scheme. Drive current is a conventional handle to modulate the QCL with bandwidths reaching up to 400 kHz [3]. Alternatively, light at another wavelength could control the QCL comb [4] as already demonstrated for THz QCL combs [5]. In this work, we take advantage of the mature near-infrared (NIR) technology to tightly-lock a MIR QCL comb to a DFB QCL using a NIR laser with a record stabilization bandwidth of 1 MHz, thus improving the spectral purity. We believe that these results are important for dual comb spectroscopy and frequency metrology in the MIR.