Monolithic high-index contrast grating: a material independent high-reflectance VCSEL mirror

Abstract

In this paper we present an extensive theoretical and numerical analysis of monolithic high-index contrast grating, facilitating simple manufacture of compact mirrors for very broad spectrum of vertical-cavity surface-emitting lasers (VCSELs) emitting from ultraviolet to mid-infrared. We provide the theoretical background explaining the phenomenon of high reflectance in monolithic subwavelength gratings. In addition, by using a three-dimensional, fully vectorial optical model, verified by comparison with the experiment, we investigate the optimal parameters of high-index contrast grating enabling more than 99.99% reflectance in the diversity of photonic materials and in the broad range of wavelengths.

Subwavelength grating as both emission mirror and electrical contact for VCSELs in any material system

“…It follows that reducing the refractive index of an SMSG semiconductor will also reduce absorption in the metallic stripes. Reducing the refractive index of an SMSG so that n  < 2 produces a low refractive index contrast between the semiconductor and air1415. This prevents the two grating modes from being guided and prevents from their destructive interference, which enables high power reflectance16.…”

“…4b, SMSGs can be constructed from any material with a refractive index greater than 1.7514 and low absorption. We chose to focus on semiconductor crystals (GaN, Al 0.8 Ga 0.2 As, GaAs, InP, Si) used in VCSELs with emission from ultraviolet to infrared.…”

“…first proposed using a grating fabricated from a monolithic crystal, achieving power reflectance as high as 85% for polarized light with a wavelength of 1550 nm. In refs 14 and 15, we showed that a monolithic HCG (MHCG) with almost 100% power reflectance could be fabricated from any transparent material with a refractive index greater than 1.75. MHCGs could therefore enable vertical stimulated emission in almost all the most common optoelectronic materials in use today, while significantly reducing the use of expensive and environmentally harmful compounds.…”

Optical examination of high contrast grating fabricated by focused-ion beam etching

“…To ensure high Fig. 1 The schematic view of an HCG structure Gębski et al (2015) Optical examination of high contrast grating fabricated by… Page 3 of 9 267…”

“…For all the obtained results, both for the HCG and the optical cavity, a reflectance of a gold mirror was used as a reference. The details of numerical calculation of HCG reflectance spectra were presented elsewhere Gębski et al (2015).…”