Raman suppression in nanophotonics enabled by multimode spectral filtering

TL;DR

This paper presents a novel multimode spectral filtering approach to suppress stimulated Raman scattering in nanophotonic devices, enabling efficient Kerr nonlinear state generation across various platforms.

Contribution

The authors introduce a versatile multimode spectral filtering strategy using nanostructured gratings and waveguides to suppress Raman effects in nanophotonics.

Findings

Demonstrated suppression of SRS in lithium niobate devices.

Achieved generation of two distinct Kerr nonlinear states.

Showcased potential for wide applicability across platforms.

Abstract

Miniaturized photonic cavities generating nonlinear optical states of light are central to telecommunications and metrology applications. The emergence of such states is primarily underpinned by the ubiquitous Kerr nonlinearity that is present in all media. However, stimulated Raman scattering (SRS), an additional process inherent to many materials, has been shown to critically hinder the states' formation, imposing fundamental constraints on the choice of photonic platforms. Here, we introduce a novel strategy for the suppression of SRS in nanophotonic devices, adaptable to diverse Raman spectral responses. This is achieved by controlling the coupling and loss among multiple transverse spatial modes of the system, tailored across ultrabroad spectral bandwidths. Specifically, we combine nanometrically-corrugated Bragg gratings and tapered waveguides that, together enable co-directional multimode coupling and mode-selective filtering. We use lithium niobate as an exemplary Raman-active material to realize the concept, and we demonstrate the robust generation of two distinct Kerr nonlinear states (corresponding to coherent optical frequency combs) using the fabricated devices. The simplicity and generality of the concept suggest wide applicability to classical and quantum light generation on many technologically-relevant platforms nominally plagued by SRS (e.g., silicon and diamond photonics). More broadly, our multimode spectral shaping and filtering concept opens a path forward for highly-structured, wavelength-specific losses in nanophotonic waveguides and cavities, with potential applications in ultrafast and nonlinear integrated photonics.