High-efficiency subwavelength-engineered surface grating couplers in SOI and DSOI

The coupling efficiency of a surface grating coupler is optimized for a an arbitrary buried oxide thickness by adjusting the grating radiation angle. The coupler is apodized using a subwavelength structure, allowing a single etch step fabrication. The measured coupling loss is −2.16dB with 3dB bandwidth of 64nm, for a minimum feature size of 100nm. It is also shown by simulations that by implementing this coupler in a double SOI (DSOI) wafer, an ultra-low coupling loss of −0.42dB is achieved.