Effect of finite grating, waveguide width, and end-facet geometry on resonant subwavelength grating reflectivity

Resonant subwavelength gratings (RSGs) offer narrowband high reflectivity with low-reflectivity sidebands. Analysis with the commonly used rigorous coupled-wave analysis assumes an RSG with infinite lateral extent and illumination by plane waves. This analysis is performed with a finite-difference semivectorial high-order accurate two-dimensional Helmholtz code that is able to simulate the entire finite RSG structure in the dimension of the grating vector. We study the effect of finite beam size on RSG reflectivity, resonant wavelength, and spectral response width. Independently, we study the effect of a finite RSG by varying the waveguide length and number of grating periods while fixing the beam size. We show that the placement of the waveguide end facets relative to the termination of the grating has a significant effect on the reflectivity and response width.