Multi-mode conversion via two-dimensional refractive-index perturbation on a silicon waveguide

TL;DR

This paper introduces a scalable, all-dielectric metastructure on silicon waveguides for simultaneous multi-mode conversion, significantly advancing on-chip mode-division multiplexing capabilities.

Contribution

It presents a novel design method for multi-mode conversion using 2D refractive-index perturbation, enabling simultaneous conversion of multiple modes with low loss and crosstalk.

Findings

Successfully demonstrated conversion from TEi to TEi+3 modes

Achieved low insertion loss (0.4-1.0 dB)

Maintained crosstalk between -14.1 to -16.5 dB

Abstract

Mode-division multiplexing offers a promising solution to increase the data capacity for optical communications. Waveguide mode conversion is essential for on-chip mode-division multiplexing. Previously reported mode converters have been limited to the conversion from a fundamental mode to one particular high-order mode. It is challenging to simultaneously satisfy the phase matching conditions during multiple mode conversion processes. Here, we propose a scalable design method that overcomes this limitation and realizes the simultaneous conversion of multiple modes via an all-dielectric two-dimensional metastructure on a silicon waveguide by shallow etching with hexagonal patterns. As an example, we experimentally demonstrate a multi-mode converter that simultaneously converts the TEi modes to the TEi+3 (i = 0, 1, 2) modes. The length of the multi-mode converter is 16.2 micron. The TE0-TE3, TE1-TE4, and TE2-TE5 mode conversions exhibit low insertion losses (0.4 to 1.0 dB) and reasonable crosstalk values (-14.1 to -16.5 dB) at 1538 nm.