The paper presents the design of a Raman supernotch filter with peak wavelength at 785 nm based on the resonant grating waveguide structure (RGWS), comprising of substrate, dielectric waveguide and polymer nanoscale-grating layers. The characteristics of the filter wavelength depend on various design and optical parameters. Rigorous coupled wave analysis is adopted to study the filter design and the effects of various design parameters on the sensitivity of the filter wavelength. Parameters such as waveguide thickness, grating periodicity, grating depth and duty cycle have been studied to achieve a supernotch filter at 785 nm, with a bandwidth of less than 2 nm and an optical density of more than 5.