Narrow Bandstop Filters with Wide and Flattened Sidebands Using Silicon-Based and Suspended Membrane Type of Guided-Mode Resonance Structures

In this paper, the simple two-layer silicon-based and suspended-membrane-type guided-mode resonance (GMR) filter with a narrow bandstop spectrum as well as wide and flattened sidebands is experimentally demonstrated. The proposed filter based on a free-standing silicon nitride membrane suspended on a silicon substrate is realized by using the anisotropic wet etching to remove the substrate beneath the silicon nitride layer. Both of grating and waveguide structures are fabricated simultaneously on a silicon nitride membrane. Moreover, the silicon dioxide membrane playing a role on modifying the spectral response of proposed GMR filter is deposited beneath the free-standing silicon nitride layer. The resonance wavelength of proposed band-stop filter is controlled at 1580.6 nm with a bandwidth less than 0.92 nm, measured in full-width at half-maximum (FWHM). The improved spectral performance including the sideband can be extended to be 415 nm with the maximum transmittance greater than 93%.