Optimal parameters of monolithic high-contrast grating mirrors

Abstract

In this Letter a fully vectorial numerical model is used to search for the construction parameters of monolithic high-contrast grating (MHCG) mirrors providing maximal power reflectance. We determine the design parameters of highly reflecting MHCG mirrors where the etching depth of the stripes is less than two wavelengths in free space. We analyze MHCGs in a broad range of real refractive index values corresponding to most of the common optoelectronic materials in use today. Our results comprise a complete image of possible highly reflecting MHCG mirror constructions for potential use in optoelectronic devices and systems. We support the numerical analysis by experimental verification of the high reflectance via a GaAs MHCG designed for a wavelength of 980 nm.

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

“…Without metal, the power reflectance is nearly 100% and the parameters are the same as those of the MHCG described in ref. 15. Increasing the contact thickness to over 50 nm reduces power reflectance, which falls to 97.9% for h Au  = 200 nm.…”

“…The thickness of the GaAs and the air beneath the mirror are assumed to be infinite. We consider a single period of the SMSG with periodic boundary conditions15, which elongates the mirror periodicity to infinity in the lateral direction. The parameters of the SMSG are as follows: L – period of the grating; h – height of the stripe below the metal in the top configuration and above the metal in the valley configuration; h M – thickness of the metal, where M is the chemical symbol of the metal; F – duty cycle, as the ratio of the width ( a ) over the period ( L ) of the stripe.…”

“…15 reduces its power reflectance drastically. The loss of power reflectance is mostly due to light being absorbed by the gold stripes.…”

“…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.…”

“…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.…”