Design of a narrowband retroreflector based on guided-mode resonance

A narrowband retroreflector consisting of a grating coupler and a waveguide cavity integrated on a highly reflective substrate is proposed. A theoretical model based on coupled-mode theories is discussed to provide analytical expression of the reflection and transmission coefficients under oblique incidence. The retroreflector was designed with a 20-µm aperture for 1540-nm-wavelength operation and 8-deg-angle incidence. Finite-difference time-domain simulation showed a retroreflection spectrum with a bandwidth of 2 nm and a maximum retroreflectance of 85% and a minimum specular reflectance of 5%.