Simple apodization technique for surface-corrugated waveguide gratings

This paper reports a simple technique for suppressing the sidelobes outside the stop band of surface-corrugated waveguide gratings. To ensure the sidelobe suppression, the dc coupling coefficient arising from the dc component of the dielectric perturbation should be as small as possible. In the proposed waveguide grating, the periodic corrugation whose depth is reduced toward the ends of the grating is formed on both sides across the film-cladding boundary of the waveguide. The 2D simulation based on the coupled-mode theory has shown that the sidelobes can be substantially suppressed while maintaining the reflection within the stop band of the uniform grating. The proposed apodization technique is suitable for the sidewall corrugation from the viewpoint of the ease of fabrication.