Broadband 2 x 2 adiabatic 3 dB coupler using silicon-on-insulator sub-wavelength grating waveguides

We report on a compact, broadband, 2 x 2 adiabatic 3 dB coupler using sub-wavelength gratings (SWGs) for silicon-on-insulator waveguides. In our device, two SWG waveguides that support two transverse electric modes and have tapered waveguide widths were used to achieve an adiabatic mode evolution of the two-waveguide system for broadband 3 dB power splitting. We present results for a SWG adiabatic 3 dB coupler that has an overall coupler length of 50 mu m and achieves broadband power splitting over a 130 nm wavelength range with an imbalance of no greater than +/- 0.3 dB and with low excess losses of less than 0.5 dB. (C) 2016 Optical Society of America