Broadband and polarization flexible SOI grating coupler based on sub-wavelength gratings with low back reflections

We propose the design of a broadband grating coupler using full-etched subwavelength gratings (SWGs) on a silicon-on-insulator platform efficiently coupling both TE and TM polarizations. Due to SWG's unique property of refractive index engineering, our design achieves a simulated 3 dB operating bandwidth of 105 nm and 121 nm for the TE and TM polarizations, respectively. Our proposed device reaches a maximum coupling efficiency of -4.88 dB at 1550 nm, exhibiting near zero polarization dependent loss at 1550 nm. Although the results are obtained from the identical SWGC design, the optimized incident angle for TE and TM are 39 degrees and 16 degrees, respectively. The back-reflections from the proposed grating coupler are suppressed to as low as -20 dB. To the best of our knowledge, our design offers the best reported performance in bandwidth and polarization sensitivity. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement