Design of a Highly Efficient Uniform Grating Coupler with Gradually Etched Grooves for Silicon-on-Insulator Waveguides

A high efficiency "uniform" grating coupler with gradually etched grooves was designed on a silicon-on-insulator substrate without experimental demonstration. For TE polarized coupling of an optical fiber at the wavelength of 1.55 μm, the fiber coupling efficiency of our grating coupler is 81%, output coupling angle is 8 degrees and 1dB spectral bandwidth is 80 nm. This performance is superior to the traditional uniform grating coupler without gradually etched grooves. Besides, our high efficiency broadband grating coupler is much easier to design than the already proposed "non-uniform" grating coupler fabricated using the lag effect of dry etching.