EVALUATION OF HR/AR MIRROR COATINGS FOR VISIBLE (RED/BLUE) LASERS

Abstract

High reflectivity (HR) and Antireflection (AR) mirror coatings play pivotal roles in improving the performance of semiconductor laser diodes. In this work, Transmission Matrix Method was realized by MATLAB programming and successfully applied to the simulation of HR/AR coatings for GaAs-based red lasers and GaN-based blue lasers. It is found that three pairs of quarterwave (HL) stacks and one quarterwave layer of AlN are able to provide a reflectivity of 93.9 % and 1.4 %, 91.0 % and 8.0 % for GaAs and GaN lasers respectively. With this HR/AR setting the stopband width of GaN lasers is 64 nm. Higher HR reflectivity and wider stopband width can be achieved by increasing the ratio of nH/nL. It is also found that, although one single AlN layer is able to provide an AR reflectivity = 10%, the margin left is not much. Therefore an AR design with an ultra-thin Si layer followed by quarterwave Al2O3 layer is proposed for lower AR reflectivity and higher COD proof.