Wavelength-Accurate Nonlinear Conversion through Wavenumber Selectivity in Photonic Crystal Resonators

TL;DR

This paper introduces a novel method for nonlinear wavelength conversion in photonic crystal resonators that achieves high wavelength accuracy and tunability without relying on dispersion engineering, enabling precise control of output wavelengths.

Contribution

The authors demonstrate a dispersion-independent approach using wavenumber selectivity via photonic bandgap effects in microresonators, allowing accurate and tunable nonlinear wavelength conversion.

Findings

Wavelength accuracy better than 0.3% achieved in experiments

Continuous tuning of output frequencies by nearly 300 GHz demonstrated

Applicable to various nonlinear processes like third harmonic generation and Kerr microcombs

Abstract

Integrated nonlinear wavelength converters transfer optical energy from lasers or quantum emitters to other useful colors, but chromatic dispersion limits the range of achievable wavelength shifts. Moreover, because of geometric dispersion, fabrication tolerances reduce the accuracy with which devices produce specific target wavelengths. Here, we report nonlinear wavelength converters whose operation is not contingent on dispersion engineering; yet, the output wavelengths are controlled with high accuracy. In our scheme, coherent coupling between counter-propagating waves in a photonic crystal microresonator induces a photonic bandgap that isolates (in dispersion space) specific wavenumbers for nonlinear gain. We first demonstrate the wide applicability of this strategy to parametric nonlinear processes, by simulating its use in third harmonic generation, dispersive wave formation in Kerr microcombs, and four-wave mixing Bragg scattering. In experiments, we demonstrate Kerr optical parametric oscillators in which such wavenumber-selective coherent coupling designates the signal mode. As a result, differences between the targeted and realized signal wavelengths are <0.3 percent. Moreover, leveraging the bandgap-protected wavenumber selectivity, we continuously tune the output frequencies by nearly 300 GHz without compromising efficiency. Our results will bring about a paradigm shift in how microresonators are designed for nonlinear optics, and they make headway on the larger problem of building wavelength-accurate light sources using integrated photonics.