Mitigating offset frequency drift in frequency combs using a customized power law dispersion

We introduce a new, to the best of our knowledge, passive technique of mitigating the phase noise in optical frequency combs (FC) by reducing the drift of offset frequency. This can be achieved by customizing the dispersion to attain a power law dependence of the wave vector on frequency, k(ω)∼ω^α, ensuring a constant ratio between group and phase velocities. When this condition is maintained, the drift offset frequency is passively mitigated, and phase noise is reduced. Using quantum cascade laser (QCL) FCs as an example, we demonstrate, analytically and numerically, that the desired dispersion can be easily engineered by properly adjusting the thickness of the QCL active region and that stable offset frequency can be combined with low residual group dispersion.