Large-angle quasi-self-collimation effect in a rod-type photonic crystal

TL;DR

This paper demonstrates a large-angle quasi-self-collimation effect in a rod-type photonic crystal with a rectangular lattice, achieved by lattice symmetry modification and characterized by a new straightness factor, with improved light coupling efficiency.

Contribution

The introduction of a straightness factor L to quantify isofrequency contour straightness and the demonstration of large-angle quasi-SC in rod-type PCs with enhanced coupling efficiency.

Findings

Straightness factor L effectively predicts quasi-SC

Large-angle quasi-SC achieved in rectangular lattice PCs

Antireflection layer improves light coupling efficiency

Abstract

A rod-type photonic crystal (PC) with a rectangular lattice shows a large-angle quasi-self-collimation (quasi-SC) effect by changing the symmetry of its rectangular lattice to straighten one of the isofrequency contours. To investigate the straightness of the isofrequency contour as well as the quasi-SC effect, we propose a straightness factor L based on the method of least squares. With L smaller than L0 (L0 = 0.01 is the critical value), the isofrequency contour is sufficiently straight to induce quasi-SC effect with the beam quasi-collimating in the structure. Furthermore, the efficiency of light coupling to the quasi-SC PC is studied, and can be greatly improved by applying a carefully designed antireflection layer.