Quasi-total backward reflection with a CRIGF under oblique incidence

We report on a numerical study of cavity resonator integrated grating filters (a grating coupler flanked with two distributed Bragg reflectors) under oblique incidence. At resonance, the diffracted energy is divided equally in four outcoupling directions, versus two directions only for the CRIGF under normal incidence and for the infinite grating coupler. We provide a simple model to demonstrate this fact. Then, we propose a configuration for which all the diffracted energy is reflected backward with respect to the direction of the incident beam, thus realizing a reflection filter free from specular reflectivity.