Design of a Thin Film Photodetector with Angular Sensitivity for Optical Micro-Encoder

In this paper, we describe a directional thin film photodetector with the objective of optical micro-encoder application. A directional photodetector with a high absorption efficiency at a specific angle of incident light is based on guided-mode resonance (GMR) of subwavelength grating. The angular sensitivity of photodetector is designed to satisfy the condition that the diffracted light from the scale grating incidents at the angle of the resonance. A numerical calculation and actual device performance are presented.