Abstract

Optical frequency combs (OFCs) generated by quantum cascade lasers (QCLs) have recently been proven in the mid infrared [1] and they have already been applied to spectroscopy in free-running operation [2]. It is clear however that for more demanding applications such as high-resolution and accuracy spectroscopy and metrology the performance obtained in free-running operation is not enough, since a consistent amount of frequency noise is present. The first attempt of frequency stabilizing a quantum cascade laser comb (QCL-comb) against a metro-logical difference-frequency-generated comb through a single phase-locking chain using the laser bias current as actuator [3] gave a reduction of the single QCL-comb tooth linewidth from 500 kHz down to values ranging from 1 to 23 kHz in a 40-ms time scale. This is still a partial result since for a total stabilization and control a second actuator is needed. Here we propose the use of feedback from a controlled mirror as a second actuator. With two actuators (at least partially independent) it is possible to correct both for offset and spacing frequency fluctuations.

© 2017 IEEE