Fabrication and characterization of high-quality uniform and apodized Si₃N₄ waveguide gratings using laser interference lithography

A method is presented for fabricating high-quality ridge waveguide gratings by combining conventional mask lithography with laser interference lithography. The method, which allows for apodization functions modulating both amplitude and phase of the grating is demonstrated by fabricating a grating that is chirped by width-variation of the grated ridge waveguide. The structure was optically characterized using both an end-fire and an infrared camera setup to measure the transmission and to map and quantify the power scattered out of the grating, respectively. For a uniform grating, we found a value of 8000 for the resonance peak near the lower wavelength band edge, which was almost completely suppressed after apodization.