Polarization-independent silicon photonic grating coupler for large spatial light spots*

We design and demonstrate a one-dimensional grating coupler with a low polarization-dependent loss (PDL) for large spatial light spots. Based on current fabrication conditions, we first utilize genetic algorithms to find the optimal grating structure including the distributions of duty and periods, making the effective refractive index of transverse electric mode the same as that of transverse magnetic mode. The designed grating coupler is fabricated on the common silicon-on-insulator platform and the PDL is measured to be within 0.41 dB covering the C-band.