Optical properties of Si/SiO2 and GaAs/AlOx sub-wavelength HCG mirrors on GaAs substrate and an impact of structural imperfections on their performance

In order to obtain low threshold VCSELs high reflectivity mirrors are crucial in their designs. Typically used Distribute Bragg Reflectors (DBR) provide reflectivity over 99.8% in the spectral range of 70 nm. To achieve polarization control numerous of shallow etchings approaches has been proposed but already lastly developed High Contrast Grating (HCG) has an ability to discard one of the mode polarization completely and additionally to provide twice broader spectrum of large reflectivity. We present simulation results of various HCG structures based on Si and GaAs high index materials combined with SiO2 and AlO_x cladding low index material layers respectively. Reflectivity simulations at 980nm wavelength show that reflectivity exceeding 99.8% can be obtained in a broad range of grating parameters. Additionally the same parameters assure very strong discrimination between TE and TM modes. Manufacturing process of a grating might involve undesirable imperfections leading to deterioration of optical properties of HCG. Hence we consider error analysis assuming random nonperiodicity of a grating structure based on Gaussian distribution of manufacture inaccuracy with standard deviation as inaccuracy measure varying from 0 nm to 50 nm. We found that inaccuracy in the range 0 nm-25 nm does not deteriorates significantly the reflection of HCG.