Coupling to multi-mode waveguides with space-time shaped free-space pulses

TL;DR

This paper explores how space-time shaped free-space pulses can selectively excite multiple modes in waveguides, offering new insights into multi-mode interactions and potential applications in nonlinear optics.

Contribution

It introduces a novel method of using space-time couplings in free-space beams to excite different modes with distinct profiles in multi-mode waveguides.

Findings

Different modes can be excited with unique complex frequency profiles

Fundamentals of mode excitation with space-time couplings are established

Potential for studying nonlinear interactions in multi-mode systems

Abstract

Guided wave optics, including most prominently fiber optics and integrated photonics, very often considers only one or very few spatial modes of the waveguides. Despite being known and utilized for decades, multi-mode guided wave optics is currently rapidly increasing in parallel with technological improvements and better simulation tools. The physics of multi-mode interactions are usually driven by some initial energy distribution in a number of spatial modes. In this work we introduce how, with free-space input beams having space-time couplings, the different modes can be excited with different complex frequency or time profiles. We cover fundamentals, the coupling with a few simple space-time aberrations, different waveguides, and a number of technical nuances. This concept of space-time initial conditions in multi-mode waveguides will provide yet another tool to study the rich nonlinear interactions in such systems.