Concept of Inverted Refractive-Index-Contrast Grating Mirror and Exemplary Fabrication by 3D Microprinting

TL;DR

This paper introduces an innovative inverted refractive-index-contrast grating (ICG) as a compact, single-layer alternative to traditional multilayered mirrors, demonstrating its design, simulation, and fabrication via 3D microprinting for advanced photonic applications.

Contribution

The paper presents the concept, numerical analysis, and experimental fabrication of the ICG, a novel single-layer mirror with polarization and phase control capabilities, fabricated using 3D microprinting.

Findings

ICG achieves near-total reflectance for refractive index > 1.75

ICG enables polarization discrimination and phase tuning

Fabrication via 3D microprinting simplifies manufacturing

Abstract

Highly reflective mirrors are indispensable components in a variety of state-of-the-art photonic devices. Typically used, bulky, multi-layered distributed Bragg (DBR) reflectors are limited to lattice-matched semiconductors or nonconductive dielectrics. Here, we introduce an inverted refractive-index-contrast grating (ICG), as compact, single layer alternative to DBR. In the ICG, a subwavelength one-dimensional grating made of a low refractive index material is implemented on a high refractive index cladding. Our numerical simulations show that the ICG provides nearly total optical power reflectance for the light incident from the side of the cladding whenever the refractive index of the grating exceeds 1.75, irrespective of the refractive index of the cladding. Additionally, the ICG enables polarization discrimination and phase tuning of the reflected and transmitted light, the property not achievable with the DBR. We experimentally demonstrate a proof-of-concept ICG fabricated according to the proposed design, using the technique of 3D microprinting in which thin stripes of IP-Dip photoresist are deposited on a Si cladding. This one-step method avoids laborious and often destructive etching-based procedures for grating structuration, making it possible to implement the grating on any arbitrary cladding material.