An Optimization of Two-Dimensional Photonic Crystals at Low Refractive Index Material

Thanh-Phuong Nguyen,Ngoc Diep Lai,Tran Quoc Tien,Quang Cong Tong

doi:10.3390/cryst9090442

Abstract

Photonic crystal (PC) is usually realized in materials with high refractive indices contrast to achieve a photonic bandgap (PBG). In this work, we demonstrated an optimization of two-dimensional PCs using a low refractive index polymer material. An original idea of assembly of polymeric multiple rings in a hexagonal configuration allowed us to obtain a circular-like structure with higher symmetry, resulting in a larger PBG at a low refractive index of 1.6. The optical properties of such newly proposed structure are numerically calculated by using finite-difference time-domain (FDTD) method. The proposed structures were realized experimentally by using a direct laser writing technique based on low one-photon absorption method.

Highlights

Photonic crystal (PC), an artificial material in which the refractive index is modulated at wavelength scale, offers presently many interesting applications in different domains [1,2]
We demonstrated an optimization of the 2D PCs to obtain a large photonic bandgap (PBG) even with low refractive index materials, such as polymer
When considering a honeycomb lattice made of air cylinders in the polymeric background, we found that the PBG only reveals for TM mode

Summary

Introduction

Photonic crystal (PC), an artificial material in which the refractive index is modulated at wavelength scale, offers presently many interesting applications in different domains [1,2]. In case of one-dimensional (1D) PCs, the PBG can be obtained by assembling multiple layers of two different materials with very low refractive indices contrast [3,4,5,6]. Different optimizations have been proposed to obtain the PBG as large as possible and with a material with a smaller refractive index. By increasing the symmetry of the PCs, for example in the case of 2D PCs, from square (four-fold) to hexagon (six-fold), and to quasi-periodic PCs, such as Penrose structure [11,12], the PBG can be opened at lower refractive index materials, such as polymers [13,14]. We demonstrated an optimization of the 2D PCs to obtain a large PBG even with low refractive index materials, such as polymer.

Theoretical Calculation

Fabrication of Proposed Structure by Direct Laser Writing Method

Conclusions