Efficient unidirectional and broadband vertical-emitting optical coupler assisted by aperture-coupled nanopatch antenna array.

Vertical-emitting optical couplers that convert in-plane guided light to out-of-plane emission are crucial elements for future photonic integrated circuits. However, traditional vertical-coupling elements, such as grating couplers, by default radiate light in both upward and downward directions, leading to a significant reduction of device efficiency. In this paper, we propose to solve this problem using a novel nanopatch antenna array, inspired by patch antenna theories commonly deployed in microwave circuits. The proposed nanopatch array features an up-to-down emission directionality up to 12.91 dBc and a wide operating bandwidth of over 400 nm simultaneously. Compared with a typical waveguide grating antenna, our design shows a significantly higher free-space gain of 24.27 dBi. The unidirectional, efficient, and broadband antenna arrays presented here are promising for a range of integrated photonics applications, including inter-chip photonic interconnects, light ranging and detection, optical communications, and biological imaging.