Special polarization characteristic features of a three-dimensional terahertz photonic crystal quantitatively evaluated by phase-differences with a FEM

TL;DR

This paper investigates the polarization features of a 3D terahertz photonic crystal using FEM, revealing why reflected wave polarization rotates by 90 degrees within the photonic band gap and identifying near-circular polarization at certain frequencies.

Contribution

It provides a quantitative analysis of polarization characteristics in a 3D THz photonic crystal, explaining polarization rotation and near-circular polarization phenomena within the PBG.

Findings

Polarization of reflected wave rotates by 90 degrees within the PBG.

Reflected wave can become near-circularly polarized at specific frequencies.

Phase-difference analysis explains the polarization behavior.

Abstract

A previous work, ref. 2 experimentally confirmed that measured special polarization characteristic features of a three-dimensional terahertz (THz) photonic-crystal did not apparently apply to general physical- and optical- basic rules. It is said that three-dimensional (3D) photonic crystals (PC) have no polarization anisotropy within photonic band gap (PBG, stop gap, stop band) of high symmetry points in normal incidence. None the less because two directions at right angles to each other on the plane (001) are constitutionally and optically identical in appearance, the polarization orientation of a reflected wave rotated by 90 degrees from that of an incident wave at a frequency within the PBG when that of the incident wave was the direction that bisects these two directions. The 3D-PC is a silicon inverse diamond structure whose lattice point shape is vacant regular octahedrons. In this work, the phase-difference, size and orientation of electric-field of the reflected wave, had been studied by using a FEM (finite element method). The analyses indicated the reason why the polarization orientation of the reflected wave is rotated by 90 degrees at the frequency within the PBG. In addition, it was found that the orbit of electric-field of the reflected wave becomes near-circularly-polarized one at another frequency within the PBG for the linear-polarization incident wave.