Experimental demonstration of polarization-insensitive air-cladding grating couplers for silicon-on-insulator waveguides

We present an air-cladding apodized focusing subwavelength grating that can effectively couple two polarizations into a single waveguide. For the transverse magnetic mode, -3.2 dB maximum coupling efficiency with similar to 28 nm 1 dB bandwidth is achieved. With the same grating, -4.3 dB maximum coupling efficiency with similar to 58 nm 1 dB bandwidth is achieved for the transverse electric mode. The minimum difference between two polarizations' coupling peaks is demonstrated to be similar to 32 nm. At the 1525 nm wavelength range, the polarization-insensitive grating is demonstrated with -6.5 dB coupling efficiency. The polarization-insensitive coupling wavelength can be controlled experimentally. (C) 2014 Optical Society of America