Resonant properties of the encapsulated grating in fused silica are studied based on the GMR effect. The planar waveguide model is used to demonstrate the resonant properties of the TE1,0, TE1,1, and TE1,2 resonances, such as the resonance locations, the confinement factor and the effective waveguide thickness. It is shown that the resonant modes of the TE1,0, TE1,1, and TE1,2 resonances are confined in a wavelength band, and the resonance locations can be tuned within this band. The mode confinement of the top layer for the TE1,0, TE1,1, and TE1,2 resonances is increased as the thickness of the top layer increases. By properly selecting the thickness of the grating layer, multiline GMR filter with different peak reflectivity can be obtained.