Recent Advances in Resonant Waveguide Gratings

Abstract

Resonant waveguide gratings (RWGs), also known as guided mode resonant (GMR) gratings or waveguide‐mode resonant gratings, are dielectric structures where these resonant diffractive elements benefit from lateral leaky guided modes from UV to microwave frequencies in many different configurations. A broad range of optical effects are obtained using RWGs such as waveguide coupling, filtering, focusing, field enhancement and nonlinear effects, magneto‐optical Kerr effect, or electromagnetically induced transparency. Thanks to their high degree of optical tunability (wavelength, phase, polarization, intensity) and the variety of fabrication processes and materials available, RWGs have been implemented in a broad scope of applications in research and industry: refractive index and fluorescence biosensors, solar cells and photodetectors, signal processing, polarizers and wave plates, spectrometers, active tunable filters, mirrors for lasers and optical security features. The aim of this review is to discuss the latest developments in the field including numerical modeling, manufacturing, the physics, and applications of RWGs. Scientists and engineers interested in using RWGs for their application will also find links to the standard tools and references in modeling and fabrication according to their needs.

Guided‐Mode Resonances in All‐Dielectric Terahertz Metasurfaces

“…The resonance phenomena in photonics allow for strong localization of electromagnetic waves that is essential for numerous applications, [1][2][3][4][5][6][7] such as narrowband filtering, [8] outof-plane wave coupling, [9] chemical and biological sensing, [10] Adv. Optical…”

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The important parameters that describe a resonance feature are its intensity and spectral linewidth. [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. Higher resonance intensity provides better signal to noise ratio, while narrower linewidth signifies larger field confinement.

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“…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.…”

“…However, most of the resonances are constrained by the trade-off between resonance intensity and linewidth. [8] Earlier reports on THz GMRs were realized through 1D grating elements on quartz substrate [33] and periodic metallic patterns on cyclo-olefin substrates. On the contrary, guided mode resonance (GMR) can provide arbitrary resonance intensity and linewidth through geometrical design and selection of materials.…”

“…[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.…”