Coupling silica waveguides to photonic crystal waveguides through multilayered Luneburg lens

TL;DR

This paper introduces a multilayered Luneburg lens coupler for efficient connection between silica and photonic crystal waveguides, achieving low coupling loss across multiple optical communication bands.

Contribution

It presents a novel multilayered Luneburg lens design and a method to optimize layer widths, improving coupling efficiency between silica and photonic crystal waveguides.

Findings

Coupling loss is lower than 0.49 dB in the C-band.

Average coupling loss across S, C, L, and U bands is 0.70 dB.

The coupler length is 2.7 μm.

Abstract

We present a detailed analysis of a coupler based on the Luneburg lens to couple a silica waveguide to a photonic crystal waveguide. The dependence of coupling efficiency on the lens's truncation, cut position of the photonic crystal structure, coupler tip width, and misalignment are investigated with two-dimensional finite element method. We implement the lens with a concentric ring-based multilayer structure. We also present a method to replace layers with very narrow widths by layers of predetermined minimum widths in the structure of the lens. The coupling loss of the designed 2.7 $\mu m$-long coupler, connecting a 2.79 $\mu m$-wide silica waveguide to a photonic crystal structure with a rod-type square lattice, is lower than 0.49 dB in the C-band. The average coupling loss in the entire S, C, L, and U bands of optical communications is 0.70 dB.