High-Efficiency Grating Couplers for Pixel-Level Flat-Top Beam Generation.

We demonstrate a kind of grating coupler that generates a high quality flat-top beam with a small beamwidth from photonic integrated circuits into free-space. The grating coupler is designed on a silicon-on-insulator wafer with a 220-nm-thick silicon layer and consists of a dual-etch grating (DG) and a distributed Bragg reflector (DBR). By adjusting the structural parameters of DG and DBR, a pixel-level (6.6 µm) flat-top beam with a vertical radiation of −0.5 dB and a mode match of 97% at 1550 nm is realized. Furthermore, a series of high-efficiency grating couplers are designed to create a flat-top beam with different scales. [ABSTRACT FROM AUTHOR]