Utilizing the glass photosensitivity. The supergratings can be fabricated with the function of wavelength-division demultiplexing in the planar waveguide. Through the study of the demultiplexing characteristics of planar waveguide supergratings based on the theory of mode coupling,the authors found that by influencing the coupling index,the angle of incident light can affect the reflectivity and bandwidth of gratings. When the incident light angle is large,although the reflectivity of the grating becomes large slightly,the bandwidth becomes wide. When the incident angle is small,although the reflectivity decreases slightly,the bandwidth becomes narrow obviously. In order to achieve the better demultiplexing performance,the requirements of reflectivity and bandwidth must be considered synthetically when designing the supergrating.