Apodization design for the focused forked grating coupler

Abstract

The Forked Grating Coupler (FGC) is a novel silicon photonics device that can interface with Optical Vortex (OV) light beams. First generation FGC devices had long adiabatic feed tapers and flat-amplitude grating apodization functions. This resulted in an inconveniently large device with degraded OV mode fidelity. New designs have been developed with a focused forked gratings allowing size to be reduced significantly. In addition, a Hamming apodization improves vortex mode fidelity within the constraint of a short focal length.