Fourier synthesis dispersion engineering of photonic crystal microrings for broadband frequency combs

TL;DR

This paper introduces a Fourier synthesis-based dispersion engineering technique for photonic crystal microring resonators, enabling broadband frequency combs with tailored spectral profiles by controlling individual mode shifts.

Contribution

It presents a novel method to engineer dispersion in microrings through Fourier synthesis, allowing arbitrary modal frequency shifts beyond traditional geometric limitations.

Findings

Demonstrated multiple dispersion profiles experimentally

Achieved broadband frequency combs with tailored spectral envelopes

Identified polarization-dependent modeling requirements

Abstract

Dispersion engineering of microring resonators is crucial for optical frequency comb applications, to achieve targeted bandwidths and powers of individual comb teeth. However, conventional microrings only present two geometric degrees of freedom -- width and thickness -- which limits the degree to which dispersion can be controlled. We present a technique where we tune individual resonance frequencies for arbitrary dispersion tailoring. Using a photonic crystal microring resonator that induces coupling to both directions of propagation within the ring, we investigate an intuitive design based on Fourier synthesis. Here, the desired photonic crystal spatial profile is obtained through a Fourier relationship with the targeted modal frequency shifts, where each modal shift is determined based on the corresponding effective index modulation of the ring. Experimentally, we demonstrate several distinct dispersion profiles over dozens of modes in transverse magnetic polarization. In contrast, we find that the transverse electric polarization requires a more advanced model that accounts for the discontinuity of the field at the modulated interface. Finally, we present simulations showing arbitrary frequency comb spectral envelope tailoring using our Frequency synthesis approach.