2 × 1D crossed strongly modulated gratings for polarization independent tunable narrowband transmission filters

Abstract

We design a narrowband polarization independent transmission guided mode resonance filter whose center wavelength is tunable with respect to the angle of incidence. The device is composed of two identical structures assembled back to back. Each half structure is a dielectric multilayer stack in which a grating is engraved. This so-called 2×1D crossed gratings component has already been demonstrated for reflection filtering [Opt. Lett.36, 1662 (2011)OPLEDP0146-959210.1364/OL.36.001662; Opt. Lett.39, 6038 (2014)OPLEDP0146-959210.1364/OL.39.006038]. The functioning in transmission requires the use of a high index material for the grating bumps. For the design, we resort to a clustering global optimization algorithm, used for the first time to our knowledge for grating structures. We demonstrated two filters with a quality factor of about 4000, tunable over more than 15 nm when the angle of incidence varies over a range of 4°, and with a transmittivity at resonance greater than 95% whatever the incident polarization.

Recent Advances in Resonant Waveguide Gratings

“…RWGs can theoretically reach 100% of reflection efficiency when their profile is vertically or horizontally symmetric or when integrated with quarter‐wave Bragg stacks . Recently, a high efficient narrowband transmission filter has been demonstrated with two crossed and strongly modulated RWGs and at normal incidence with partially etched single‐layer RWG . RWGs can also be utilized to make efficient wideband reflectors using a periodic array of high‐index scatterers on a low index layer (Figure b,c) .…”

Guided‐Mode Resonances in All‐Dielectric Terahertz Metasurfaces

“…For most practical applications, resonances with strong intensity and narrow linewidth are desirable. [8,[21][22][23][24][25][26][27][28][29][30][31] The GMR filter primarily comprises of a diffractive grating and an in-plane waveguide. However, most of the resonances are constrained by the trade-off between resonance intensity and linewidth.…”

“…[35] The 2D array of silicon cuboid resonators acts as a grating and more importantly, the silicon metasurface also acts as a homogeneous core layer that support slab waveguide modes, governed by total internal reflection (TIR) [36] (see Supporting Information for details). The combination of the waveguiding criteria (i.e., TIR) and the grating equation provides the critical condition for the realization of GMR, which is given by: n sin [8,[21][22][23][24][25][26][27][28][29][30][31][32][33]36] where Λ is the lattice period, λ is wavelength and the corresponding frequency is given by f = c/λ . The modes that lie above the light line are radiative in nature, while those lying below are guided within the slab waveguide.…”

“…[8] Due to this versatile nature of GMRs, they have found wide range of applications, including extremely high-Q filters, ultrabroadband reflectors, wavelength selective polarizers, and beam splitters. [8,[21][22][23][24][25][26][27][28][29][30][31] The GMR filter primarily comprises of a diffractive grating and an in-plane waveguide. The grating diffracts the incident light and couples it into the waveguide, which propagates as a guided mode.…”

“…Due to band folding, the guided modes now fall above the light line and hence become guided resonances that couple to the radiating modes of the cladding. The combination of the waveguiding criteria (i.e., TIR) and the grating equation provides the critical condition for the realization of GMR, which is given by: n sin [8,[21][22][23][24][25][26][27][28][29][30][31][32][33]36] where Λ is the lattice period, λ is wavelength and the corresponding frequency is given by f = c/λ . By solving the GMR equation, a pair of GMRs can be readily achieved as a function of θ (see Supporting Information for details).…”