Under certain conditions, a resonance phenomenon can occur in waveguide grating structures. Such structures have multilayer configuration, the most basic of which is comprised of a substrate, a thin dielectric layer or semiconductor waveguide layer, and an additional transparent layer in which a grating is etched. When such a structure is illuminated with an incident light beam, part of the beam is directly transmitted and part is diffracted and subsequently trapped in the waveguide layer. Some of the trapped light is then rediffracted outwards, so that it interferes destructively with the transmitted part of the light beam. At a specific wavelength and angular orientation of the incident beam, the structure "resonates"; namely, complete interference occurs and no light is transmitted. This paper reviews previous investigations on the resonance phenomena and presents analytic and numerical models for evaluating the resonance as a function of the geometric and optical parameters of the structures and incident radiation.

Resonant grating waveguide structures

Optical reflection, or in other words the loss of reflection, from a surface becomes increasingly crucial in determining the extent of the light-matter interaction. The simplest example of using an anti-reflecting (AR) surface is possibly the solar cell that incorporates an AR coating to harvest sunlight more effectively. Researchers have now found ways to mimic biological structures, such as moth eyes or cicada wings, which have been used for the AR purpose by nature herself. These nanoscopic biomimetic structures lend valuable clues in fabricating and designing gradient refractive index materials that are efficient AR structures. The reflectance from a selected sub-wavelength or gradient index structures have come down to below 1% in the visible region of the spectrum and efforts are on to achieve broader bands of such enhanced AR regime. In addition to the challenge of broader bands, the performance of AR structures is also limited by factors such as omnidirectional properties and polarization of incident light. This review presents selected state-of-the-art AR techniques, reported over the last half a century, and their guiding principles to predict a logical trend for future research in this field.

Anti-reflecting and photonic nanostructures

Periodic structures with a sub-wavelength pitch have been known since Hertz conducted his first experiments on the polarization of electromagnetic waves. While the use of these structures in waveguide optics was proposed in the 1990s, it has been with the more recent developments of silicon photonics and high-precision lithography techniques that sub-wavelength structures have found widespread application in the field of pho- tonics. This review first provides an introduction to the physics of sub-wavelength structures. An overview of the applications of sub-wavelength structures is then given including: anti-reflective coatings, polarization rotators, high-efficiency fiber-chip cou- plers, spectrometers, high-reflectivity mirrors, athermal waveg- uides, multimode interference couplers, and dispersion engi- neered, ultra-broadband waveguide couplers among others. Particular attention is paid to providing insight into the design strategies for these devices. The concluding remarks provide an outlook on the future development of sub-wavelength structures and their impact in photonics.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.201400083

Waveguide sub-wavelength structures: a review of principles and applications

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.

/pdf/recent-advances-in-resonant-waveguide-gratings-17dyntevmn.pdf

Recent Advances in Resonant Waveguide Gratings

In this paper, we address resonant leaky-mode reflectors made with a periodic silicon layer on an insulating substrate. Our objective is to explain the physical basis for their operation and to quantify the bandwidth provided by a single resonant layer by illustrative examples for both TE and TM polarized incident light. We find that the number of participating leaky modes and their excitation conditions affect the bandwidth. We show that recently reported experimental [1, 2] wideband reflectors operate under leaky-mode resonance. These compact reflectors are new elements with many potential applications in photonic systems. The results presented explaining their physical basis will aid in their continued development.

https://profdoc.um.ac.ir/articles/a/1024435.pdf

Physical basis for wideband resonant reflectors.

It is shown that reflection of a plane monochromatic wave by the surface of a corrugated waveguide structure may excite a guided mode in one of the diffraction orders and thus alter greatly the reflection and transmission coefficients of the incident wave until total reflection or total transmission are achieved.

http://iopscience.iop.org/article/10.1070/QE1985v015n07ABEH007275/pdf

Total reflection of light from a corrugated surface of a dielectric waveguide

Experimental results on the formation of antire-flective periodical microrelief on the surface of CVD diamond films are presented. Diamond surface microstructuring was performed by a laser ablation technique by using either a tightly focused beam of a Nd:YAP laser (λ=1078nm) or a projection optical scheme with a KrF excimer laser (λ= 248 nm). The minimal period of the produced one- and two-dimensional surface gratings, consisting of parallel microgrooves or microcraters, was 3 μm. The optical transmission of the structured diamond surface was found to increase in the IR spectral region depending on the relief depth. The rise of the transmission at a wavelength of 10.6 μm from 70% to 80% was achieved for the diamond films, both sides of which were patterned.

Formation of antireflective surface structures on diamond films by laser patterning

A study is made of the spectral characteristics of selectively reflecting mirrors in the form of a plane-parallel substrate on the surface of which a corrugated optical waveguide is formed. It is shown that a resonance coupling between the modes excited in the waveguide determines the spectral profile of the reflection line obtained for normal incidence of a beam. It is shown that the use of such mirrors in a laser resonator should improve the distribution of the laser radiation field in the far zone.

Spectral and laser characteristics of a mirror with a corrugated waveguide on its surface

Grating coupling is now currently used in evanescent-wave biochemical sensors as a waveguide coupling element or as the sensing element. In most coupling cases of practical interest, the Rayleigh-Fourier method is valid, and leads to physically meaningful analytical solutions allowing grating coupling to be designed in simple terms. In the present paper the emphasis is placed on the grating as a waveguide coupling element.

/pdf/waveguide-coupling-gratings-for-high-sensitivity-biochemical-23i17ib0ms.pdf

Waveguide coupling gratings for high-sensitivity biochemical sensors

Light reflection from a corrugated waveguide is studied and application is made to dispersive elements in dye lasers.

A V Tishchenko

Papers

Total reflection of light from a corrugated surface of a dielectric waveguide

Formation of antireflective surface structures on diamond films by laser patterning

Spectral and laser characteristics of a mirror with a corrugated waveguide on its surface

Waveguide coupling gratings for high-sensitivity biochemical sensors

Light reflection from the surface of a corrugated waveguide