Design of integrated-photonic retroreflectors for oblique incidence of diverging wave

A wavelength-selective retroreflector based on guided-mode resonance (GMR) was proposed for an external cavity mirror of semiconductor lasers. The device, called a focusing cavity-resonator-integrated GMR filter (F-CRIGF), consists of a focusing grating coupler (FGC) integrated in a distributed-Bragg-reflector cavity on a bottom mirror. The F-CRIGF was designed for a 1550-nm-wavelength Gaussian beam whose axis is tilted by 20 degrees from the device’s surface normal. The FGC length and the focal length were 30 μm and 31.2 μm, respectively. A peak retro-reflectance of 68% with a 1.5-nm bandwidth was predicted by two-dimensional finite-difference time-domain simulation.