Fig. 1. Geometry of (a) a conventional three-layer resonant structure and (c) the proposed two-groove planar filter, and (b) the refractive (effective refractive) index profile of the structure. The values in (b) and dimensions in (c) correspond to one of the examples described in the text. I, R, and T denote incident, reflected, and transmitted waves, respectively.

Fig. 2. (a) Angular and (b) wavelength TGPF transmission spectra at hcl=400  nm (dashed blue curves) and hcl=600  nm (solid red curves). The insets show the FWHM of the resonant peaks versus hcl.

Fig. 3. Distributions of the |Hy|2 component of the electromagnetic field in the TGPF normalized by the maximum |Hy|2 value of the incident guided mode at hcl=400  nm and θ=θ1 for the free-space wavelengths (a) 600, (b) 620, and (c) 630 nm.

Fig. 4. Calculated transmittance spectra at varying ridge widths hwg ranging from 87.5 nm (leftmost peak) to 112.5 nm (rightmost peak) in steps of 2.5 nm. Colors of the curves correspond to the resonant wavelengths at each ridge width value.

Fig. 5. Transmittance spectra of the TGPF with hwg=100  nm, hcl=600  nm (dashed blue curve), and of the planar structure consisting of two TGPFs separated by an additional groove with a width of 198 nm (shown in the inset) (solid red curve).