A shallow grating triple-layer guided-mode resonance (GMR) filter and its properties are presented. For this type of GMR filter, the grating layer has the equal refractive index to the waveguide layer. It is shown that the GMR filter with shallow grating has good characteristics of narrow bandwidth, symmetrical line shape, and low-reflection sideband. The spectral FWHM of the GMR filter can be controlled by varying the grating thickness. The desired FWHM at the same resonance wavelength with symmetrical line shape and low-reflection sideband can be obtained by adjusting the grating thickness and the grating period with the total thickness of the grating and waveguide layers kept unchanged.
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