Nonvertical Sidewall Angle Influence on the Efficiency of Diamond‐on‐Insulator Grating Couplers

Abstract

Planar devices for light transmission between diamond integrated optical circuits and optical fibers or microscope objectives (called grating couplers) can be fabricated by capacitively coupled reactive ion etching (RIE) through contact hard masks micropatterned by e-beam lithography. However, sidewalls of such etched structures cannot be vertical because their steepness is limited by etching conditions. This study is devoted to numerical simulations of wall steepness influence on diamond-based grating coupler efficiency at 637 and 1550 nm wavelengths. A simple genetic algorithm to find the optimal device geometry is used herein. The maximum grating coupler efficiency remains almost constant at the wall steepness from 90 to 60 and decreases at lower values. In the specified range, changes in the wall steepness can be fully compensated by changing the width of grating coupler ridges (fill factor). Lowering the wall steepness gives rise to other parameters' tolerances. The study proves that fast and robust capacitively coupled RIE of diamond is a suitable method for creating diamond grating couplers.