High-Efficiency Grating Couplers Near 1310 nm Fabricated by 248-nm DUV Lithography

We demonstrate a highly efficient grating coupler with center wavelength near 1310 nm fabricated on a silicon-on-insulator (SoI) wafer by 248-nm deep ultraviolet lithography. One of the lowest reported losses of 2 dB is achieved using feature sizes of 200 nm and without other process enhancements, such as polysilicon. The higher efficiency is obtained through improved mode-matching based on a novel genetic algorithm, which utilizes two different etch depths. The 3-dB bandwidth is 50 nm, and the back-reflection to the waveguide is better than 20 dB. The result shows low-loss coupling between waveguides and single-mode fibers for 1310~nm applications suitable for mass production on the commonly used 220-nm SoI platform.