CMOS-Compatible Polarization Splitting Grating Couplers With a Backside Metal Mirror

We present a highly efficient 1-D grating structure that serves to couple light between standard optical fibers and single-mode waveguides in the silicon-on-insulator platform and to split both orthogonal polarization states. The efficiency of the fabricated coupler is enhanced by a backside metal mirror and reaches -2.4 dB for both polarizations at 1552 nm with an extinction ratio >25 dB in a wide wavelength range. The efficiency can be theoretically improved to -1.1 dB when optimizing the number of periods and using a nonuniform grating.