Non-resonant Optical Injection Locking in Quantum Cascade Laser Frequency Combs

Abstract: Optical injection locking of the repetition frequency of a quantum cascade laser frequency comb is demonstrated using an intensity modulated near-infrared light at 1.55 $\mu$m illuminating the front facet of the laser. Compared to the traditional electrical modulation approach, the introduced technique presents benefits from several perspectives such as the availability of mature and high bandwidth equipment in the near-infrared, circumvent the need of dedicated electronic components for the quantum cascade laser, and allows a direct link between the near and mid-infrared for amplitude to frequency modulation. We show that this stabilization scheme, used with moderate near-infrared power of a few milliwatts, allows for a strong reduction of the frequency noise. We also perform a full characterization of the mechanism and evidence that the locking range follows Adler's law. A comparison of our results with those in recent literature indicates that the optical approach leads to better performance compared to the traditional method, which we expect to benefit mid-infrared spectroscopy and metrological applications.