In the light of the rigorous coupled wave theory and equivalent medium theory

this paper presents the structure of and design method for GaN-based subwavelength guided-mode resonant grating filters for C band of optical communications and discusses in detail the effects of grating period and incident angle on the resonant wavelength of the filter reflectance spectrum under the actions of high duty cycle of strongly modulated grating.While keeping the filtering effects as high diffraction efficiency（resonant wavelength peak reflectivity above 99.5%）

low sideband reflection and narrow linewidth

it uses its sensitivity to the incident angle and in combination with the numerical simulation presents a method for tuning the incident angle（0

4

.07°）by a MEWS planar reflector

thus linearly controlling the resonant wavelength output in a tuning range of 36 nm and realizing a tunable filter with FWHM lower than 0.8nm for C band of optical communication networks.