Fabrication and Analysis of Three-Layer All-Silicon Interference Optical Filter with Sub-Wavelength Structure toward High Performance Terahertz Optics

TL;DR

This paper presents a novel all-silicon three-layer interference filter with sub-wavelength structures designed for high-performance terahertz optics, demonstrating fabrication and theoretical validation of its optical properties.

Contribution

It introduces a new all-silicon multi-layer interference filter with sub-wavelength structures, fabricated using MEMS technologies, and validates its optical performance through experiments and simulations.

Findings

Measured transmittance matches theoretical calculations.

SWS layers act as homogeneous thin-film layers with effective refractive indices.

Prototype demonstrates robustness and potential for practical THz optical filters.

Abstract

We propose an all-silicon multi-layer interference filter composed solely of silicon with sub-wavelength structure (SWS) in order to realize high performance optical filters operating in the THz frequency region with robustness against cryogenic thermal cycling and mechanical damage. We demonstrate fabrication of a three-layer prototype using well-established common micro-electro-mechanical systems (MEMS) technologies as a first step toward developing practical filters. The measured transmittance of the three-layer filter agrees well with the theoretical transmittances calculated by a simple thin-film calculation with effective refractive indices as well as a rigorous coupled-wave analysis simulation. We experimentally show that SWS layers can work as homogeneous thin-film interference layers with effective refractive indices even if there are multiple SWS layers in a filter.