Intermodal group velocity engineering for broadband nonlinear optics

TL;DR

This paper introduces a method to engineer group velocities in multi-mode optical fibers, enabling broadband intermodal nonlinear interactions and the creation of tunable fiber lasers with unprecedented bandwidths.

Contribution

It demonstrates a novel approach to tailor phase matching bandwidth in multi-mode fibers through group velocity engineering, expanding nonlinear optics capabilities.

Findings

Achieved >60 nm gain bandwidth in four-wave mixing at 1550 nm.

Generated a high-peak-power tunable fiber laser in the Ti:Sapphire regime.

Showcased broadband, wavelength-agnostic nonlinear optical platform.

Abstract

Interest in the nonlinear properties of multi-mode optical waveguides has seen a recent resurgence on account of the large dimensionality afforded by the platform. However, a perceived fundamental limitation of intermodal parametric interactions - that they are impractically narrowband - has yet to be solved. Here we show that by engineering the relative group velocity within the discrete spatial degree of freedom, we can tailor the phase matching bandwidth of intermodal parametric nonlinearities. We demonstrate group-velocity-tailored four-wave mixing between the $LP_{0,4}$ and $LP_{0,5}$ modes of a multi-mode fiber with unprecedented gain bandwidths (>60 nm at ~1550 nm). As evidence of the technological utility of this methodology, we seed this process to generate a high-peak-power wavelength-tunable fiber laser in the Ti:Sapphire wavelength regime. More generally, with the combination of intermodal interactions, which dramatically expand the phase matching degrees of freedom for nonlinear optics, and intermodal group velocity engineering, which enables tailoring the bandwidth of such interactions, we showcase a platform for nonlinear optics that can be broadband while being wavelength agnostic.