Angle Of Total Internal Reflection Research Articles

Surface Electromagnetic TE-Waves Total Internal Reflection

We have considered the refraction of surface electromagnetic waves (SEW) at the heterogeneous metasurface. The considered structure consists of three regions: mu-negative metamaterial, ordinary magnetic, and vacuum. The boundaries between considered media are planar. A phenomenological approach was used; media were assumed to be lossless and isotropic. In this paper, we show the possibility of total internal reflection effect for SEW of TE-polarization that can propagate along such heterogeneous metasurface. The value of the angle of total internal reflection decreases for higher frequency waves from the interval under consideration. The presented result may help design both research and industry complex systems.

Theoretical optimization of a frequency-domain- based color polarization interference sensor viacoupling with a Gaussian beam.

In this paper, a Gaussian-beam-coupled color polarization interference (CCPI) sensor with an adjustable digital Gaussian filter was proposed theoretically in the frequency domain. The coupling principle of a traditional color polarization interference (CPI) sensor and a Gaussian beam was investigated, and sensitivity optimization was then implemented. The formation of a doublet is related to the shape of a CPI curve, expected wavelength, and FWHM of the Gaussian beam. Based on the calculated results, the angle between the two polarizers and the obliquity of the wave plate are the two most significant adjusting parameters. The sensitivity of a CCPI sensor is approximately twofold higher than that of a traditional CPI sensor. The sensing range is also related to the FWHM of the Gaussian beam and a larger FWHM usually means a wider sensing range. We also found that the sensitivity would reach a maximum when the incident angle is near the total internal reflection angle. Besides, a longer incident wavelength usually corresponds to a higher sensitivity and the sensitivity could reach as high as 9270nm/refractive index unit when the resonance wavelength is 977.40nm.

Polymer-Based Optical Waveguide Tactile Sensing Method for 3-D Surfaces

At present, most tactile sensors are fabricated based on the flat surface, which greatly limits their applications in the 3-D scenario. To deal with the bottleneck, this article proposes a polymer-based optical waveguide sensing method. The waveguide can be integrally formed along a channel within a 3-D surface. Microbending light loss of a waveguide is the sensing principle. By studying the linearity between the degree of microbending and light loss, the feasibility analysis of spherical tactile sensing element (tactile) was completed, as well as the basis for size selection of it. In addition, the key to layout on 3-D surface of the proposed sensing method is that the bending radius of the waveguide is within the critical angle of total internal reflection (TIR). By normalizing the ratio of the side length of the cross Section to the bending radius, it is shown that the light loss does not increase when the proportionality coefficient is less than 0.3. The experiment is validated by embedding four tactiles in a 3-D surface. The cross Section of the waveguide is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times1.5$ </tex-math></inline-formula> mm. We demonstrated that the static hysteresis error for a tactile is less than 16% within 595 kPa, the best sensing sensitivity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1}.{42} \times {{10}}^{-{5}} {}{\text {kPa}}^{-{1}}$ </tex-math></inline-formula> , and the maximum measurement range is from 0 to 850 kPa. As for the dynamic measurement, the tactile can rapidly response the signal change with given frequencies (the maximum is 10 Hz). The average delay time is around 12 ms.

Actively tunable weak and strong couplings in epsilon-near-zero ultrathin film-based Weyl semimetallic photonic crystals

Lithography-free layered dielectric media plays an important role in photonic platforms and opens up new possibilities in the design of devices with large-scale compatibilities. In this work, we propose a hybrid structure consisting of phononic thin layer and Weyl semimetallic photonic crystals. Manipulation of electromagnetic waves and the interactions between different optical modes are presented, which is highly demanded for both fundamental research and practical applications. The weak and strong coupling effects result in hybrid polariton modes, of which the dispersion can be quantitatively described by a coupled harmonic oscillator model. In the Kretschmann coupling proposal, when the incident angle is smaller than the critical angle (θ c = 25∘) of total internal reflection, a weak coupling is generated. However, when the incident angle is larger than θ c , anticrossing resluts from strong coupling can be observed. We believe that the use of easily manufactured WSM elements and the tunable hybridization of multiple optical modes will enable the manipulation of light-matter interactions with more flexibility in the mid-infrared range, and can significantly improve the functional properties of various devices.

Metasurfaces Excited by an Evanescent Wave for Terahertz Beam Splitters with a Tunable Splitting Ratio

In terahertz (THz) photonics, a beam splitter is an important component. Although various THz beam-splitting devices using several principles have been proposed, the splitting ratio of existing designs is not adjustable. Here, a THz beam splitter with an adjustable splitting ratio is demonstrated using a metasurface integrated onto a prism. The metasurface excited by an evanescent wave can convert part of a linearly polarized incident wave into a cross-polarized wave and manipulate its phase simultaneously. As a result, the cross-polarized wave can pass through the interface, even if the incident angle is larger than the total internal reflection angle, while the co-polarized wave is reflected by the prism. The splitting ratio of the device can be adjusted from 4.56:1 to 0.63:1 by tuning the resonant response of the metasurface and varying the interval distance between the metasurface and the prism. The metasurface samples are fabricated using low-cost standard printed circuit technology, and the experimental results are consistent with the simulations. Therefore, the proposed beam splitter with a tunable splitting ratio is promising as a key component in the THz system.

Coupling interactions of anisotropic hyperbolic phonon polaritons in double layered orthorhombic molybdenum trioxide

The natural hyperbolic phonon polariton material-orthorhombic molybdenum trioxide (α-MoO&lt;sub&gt;3&lt;/sub&gt;) has recently attracted much interest , due to the associated ultra-confinement of light and enhanced light-matter interactions. We theoretically propose and study the in-plane anisotropic phonon polaritons (APhPs) in the Kretschmann structure with monolayer and dual layers α-MoO&lt;sub&gt;3&lt;/sub&gt;. The excitation of phonon polaritons and the corresponding dispersion properties in this multilayer system are studied by using a generalized 4×4 transfer matrix method (TMM). The frequency dispersions with geometrical parameters are also discussed in detail. The results confirm that the interlayer coupling can be modulated by stacking the multilayer films and regulating the thickness of each layer. More interestingly, when the distance between double α-MoO&lt;sub&gt;3&lt;/sub&gt; layers is much smaller than the propagation length of PhPs, a strong coupling phenomenon occurs, and the photon tunneling probability and intensity can be greatly improved. When the incident angle is greater than the total internal reflection angle, the phase matching condition for SPhP excitation can be satisfied. Within the 40° incident angle, the SPhP blue-shifts rapidly with the increase of incident angle. But then the dispersion curve no longer changes with increase of incidence angle. The enlargement of the interstitial layer can also lead the Fabry-Perot (FP) resonance mode to be excited. The APhP in layered heterostructure is an important part of today's nanophotonic technology, our study can help optimize and design tunable optoelectronic devices based on hyperbolic materials.

Ray Optics for Gliders.

Control of self-propelled particles is central to the development of many microrobotic technologies, from dynamically reconfigurable materials to advanced lab-on-a-chip systems. However, there are few physical principles by which particle trajectories can be specified and can be used to generate a wide range of behaviors. Within the field of ray optics, a single principle for controlling the trajectory of light─Snell's law─yields an intuitive framework for engineering a broad range of devices, from microscopes to cameras and telescopes. Here we show that the motion of self-propelled particles gliding across a resistance discontinuity is governed by a variant of Snell's law, and develop a corresponding ray optics for gliders. Just as the ratio of refractive indexes sets the path of a light ray, the ratio of resistance coefficients is shown to determine the trajectories of gliders. The magnitude of refraction depends on the glider's shape, in particular its aspect ratio, which serves as an analogue to the wavelength of light. This enables the demixing of a polymorphic, many-shaped, beam of gliders into distinct monomorphic, single-shaped, beams through a friction prism. In turn, beams of monomorphic gliders can be focused by spherical and gradient friction lenses. Alternatively, the critical angle for total internal reflection can be used to create shape-selective glider traps. Overall our work suggests that furthering the analogy between light and microscopic gliders may be used for sorting, concentrating, and analyzing self-propelled particles.

Infrared radiation transfer through semitransparent windows supporting absorbing droplets

Water droplets are commonly observed on the inner or outer surface of solar energy conversion systems due to rain or condensation. These droplets affect the systems’ efficiency and thermal load. This study experimentally and numerically investigates infrared radiation transfer through semitransparent windows covered with droplets on their front or back sides. In order to validate our previously developed numerical code and to facilitate the systematic characterization of the samples, acrylic droplets (instead of water) were deposited onto glass windows with contact angle ranging from 26 to 76° and projected surface area coverage from 0% to 60%. The measured transmittance of glass windows with slightly absorbing droplets on the front increased while the reflectance decreased with increasing contact angle and surface coverage due to antireflection effects. For slightly absorbing droplets on the back with contact angles larger than the critical angle for total internal reflection at the droplet/air interface, the transmittance decreased by up to a factor 2 with increasing contact angle and surface area coverage. In the infrared spectral range when droplets were strongly absorbing, the window transmittance decreased by up to a factor 2.5 with increasing surface coverage for droplets either on the front or back sides. Experimental measurements were in excellent agreement with numerical predictions obtained using the Monte Carlo ray-tracing method. Then, the experimentally-validated simulation tool was used to predict the solar transmittance and emittance of glass windows covered with water droplets. The solar transmittance was found to decrease significantly with water droplets on either side depending on the time of day while the emittance remained unchanged.

Analysis and optimization of graphene based reconfigurable electro-optical switches

We consider a planar layered structure including a graphene sheet with an unexpected transmission of the beam in total internal reflection angles. In this paper, we investigate this particular response through the excitation of leaky type surface plasmons of graphene and the coupling of surface plasmons to far-field radiations. Dependence of the transmission on the chemical potential of graphene is investigated and maximized by optimization techniques. Thus, for a fixed frequency and angle of incident beam, the transmission coefficient can be set between 0 and a maximum value (up to more than 0.9) by tuning the chemical potential of graphene via the applied voltage. This effect can be used in design of tunable optoelectronic frequency/angle switches.

Magnonic Metamaterials for Spin-Wave Control with Inhomogeneous Dzyaloshinskii-Moriya Interactions.

A magnonic metamaterial in the presence of spatially modulated Dzyaloshinskii–Moriya interaction is theoretically proposed and demonstrated by micromagnetic simulations. By analogy to the fields of photonics, we first establish magnonic Snell’s law for spin waves passing through an interface between two media with different dispersion relations due to different Dzyaloshinskii–Moriya interactions. Based on magnonic Snell’s law, we find that spin waves can experience total internal reflection. The critical angle of total internal reflection is strongly dependent on the sign and strength of Dzyaloshinskii–Moriya interaction. Furthermore, spin-wave beam fiber and spin-wave lens are designed by utilizing the artificial magnonic metamaterials with inhomogeneous Dzyaloshinskii–Moriya interactions. Our findings open up a rich field of spin waves manipulation for prospective applications in magnonics.

Light Scattering by a Subwavelength Plasmonic Array: Anisotropic Model.

We calculate the light transmission by a subwavelength plasmonic array using the boundary element method for parallel cylinders with different cross-sections: circular or elliptic with axis ratio 4:1. We demonstrate that plasmonic resonance is sharper for the case of horizontal ellipses. This structure is susceptible to refractive index variations in the media since the high derivatives of reflection and transmission coefficients are near the angle of total internal reflection. To obtain an approximate analytical expression, we used the model of a metallic layer. We explore the “sandwich” structure with an anisotropic film between two dielectrics and demonstrate its quantitative agreement with numerical results.

Dual-detection-parameter SPR sensor based on graded index multimode fiber

In this paper, a dual-detection-parameter SPR sensor for micro angle and micro displacement measurement was fabricated by using graded index multimode fiber. By employing mathematical modeling and theoretical simulation, the micro angle and micro displacement sensing properties of the graded index multimode fiber were studied and verified based on its special light transmission characteristics. The simulation results indicated that the total internal reflection angle (SPR incident angle) of the graded index multimode fiber was sensitive to the deviation angle and deviation displacement of the incident light. The experimental results showed that the wavelength sensitivity and light intensity sensitivity of the micro angle sensor was 2.417 nm/° and 0.236 a.u./°, respectively. And the wavelength sensitivity and light intensity sensitivity of the micro displacement sensor is 0.7084 nm/° and 0.0236 a.u./°, respectively. The dual-detection-parameter fiber SPR sensor is simple, stable and not easy to be damaged, which can be easily applied in various fields of micro angle and micro displacement measurement.

A simple and comprehensive electromagnetic theory uncovering complete picture of light transport in birefringent crystals

Birefringence production of light by natural birefringent crystal has long been studied and well understood. Here, we develop a simple and comprehensive rigorous electromagnetic theory that allows one to build up the complete picture about the optics of crystals in a friendly way. This theory not only yields the well-known refraction angle and index of ellipse for birefringence crystal, but also discloses many relevant physical and optical quantities that are rarely studied and less understood. We obtain the reflection and transmission coefficient for amplitude and intensity of light at the crystal surface under a given incident angle and show the electromagnetic field distribution within the crystal. We derive the wavefront and energy flux refraction angle of light and the corresponding phase and ray refractive index. We find big difference between them, where the phase refractive index satisfies the classical index of ellipse and Snell’s law, while the ray refractive index does not. Moreover, we disclose the explicit expressions for the zero-reflection Brewster angle and the critical angle for total internal reflection. For better concept demonstration, we take a weak birefringent crystal of lithium niobate and a strong birefringent crystal tellurium as examples and perform simple theoretical calculations. In addition, we perform experimental measurement upon z-cut lithium niobate plate and find excellent agreement between theory and experiment in regard to the Brewster angle. Our theoretical and experimental results can help to construct a clear and complete picture about light transport characteristics in birefringent crystals, and may greatly facilitate people to find rigorous solution to many light–matter interaction processes happening within birefringent crystals, e.g., nonlinear optical interactions, with electromagnetic theory.

The Elaboration of Effective Coatings for Photonic Crystal Chips in Optical Biosensors.

Here, we propose and study several types of quartz surface coatings designed for the high-performance sorption of biomolecules and their subsequent detection by a photonic crystal surface mode (PC SM) biosensor. The deposition and sorption of biomolecules are revealed by analyzing changes in the propagation parameters of optical modes on the surface of a photonic crystal (PC). The method makes it possible to measure molecular and cellular affinity interactions in real time by independently recording the values of the angle of total internal reflection and the angle of excitation of the surface wave on the surface of the PC. A series of dextrans with various anchor groups (aldehyde, carboxy, epoxy) suitable for binding with bioligands have been studied. We have carried out comparative experiments with dextrans with other molecular weights. The results confirmed that dextran with a Mw of 500 kDa and anchor epoxy groups have a promising potential as a matrix for the detection of proteins in optical biosensors. The proposed approach would make it possible to enhance the sensitivity of the PC SM biosensor and also permit studying the binding process of low molecular weight molecules in real time.

Optofluidic Resonance of a Transparent Liquid Jet Excited by a Continuous Wave Laser

We report a new optofluidic resonating phenomenon that naturally links the optical radiation pressure, total internal reflection, capillary wave, and Rayleigh-Plateau instability together. When a transparent liquid jet is radiated by a focused continuous wave laser beam, the highly ordered periodic jet breakup is unexpectedly triggered and maintained. The capillary wave enables the liquid-gas interface to serve as a rotating mirror reflecting the laser beam in a wide range of angles, including the critical angle for total internal reflection. The liquid jet acts as an optical waveguide to periodically transmit the laser beam to the upstream of the jet. The periodic optical beam transmittance inside the liquid jet exerts time-dependent optical pressure to the jet that triggers the Rayleigh-Plateau instability. The jet breakup process locks in at the frequency corresponding to the peak growth rate of the Rayleigh-Plateau instability of the liquid jet, which agrees with the prediction from the dispersion relation of a traveling liquid jet.

Waveguide-type see-through dual focus near-eye display with a polarization grating.

Waveguide-type near-eye displays have useful properties such as compact form factor, lightweight and see-through capability. Conventional systems, however, support only a single image plane fixed at a certain distance, which may induce eye fatigue due to the vergence-accommodation conflict. In this paper, we propose a waveguide-type near-eye display with two image planes using a polarization grating. Two images with orthogonal polarizations propagate within the waveguide with different total internal reflection angles and form virtual images at different distances. The use of the polarization grating and two pairs of holographic optical elements enables dual image plane formation by a single waveguide with high transparency for the real scene. Optical experiments confirm the principle of the proposed optical system.

Modelling of ATR-FTIR MEMS Spectrometer Under Partially-Coherent Multimode-Fiber Illumination

Miniaturization of attenuated total reflectance (ATR) spectrometers has been an emerging field applying such powerful surface sensing method for in-situ spectroscopic analysis. In this work, we present a model for field propagation through ATR element under the illumination of multimode fiber (MMF) in a micro-electro-mechanical-systems (MEMS) based ATR Fourier transform infrared (FTIR) spectroscopic system. The core spectrometer is based on micro-fabricated Michelson interferometer using deep etching technology, in which the light propagates in-plane with respect to the silicon substrate. An ATR multiple reflection crystal is illuminated with infrared (IR) thermal blackbody radiation source through an MMF. The output light of the crystal is fiber-coupled to the MEMS interferometer then to an IR broadband photodetector. The optical system is modelled using scaler Fourier optics, where the fiber output field is represented by a group of spatially shifted elementary sources, to predict the ATR absorbance response, taking into account the partial spatial coherence nature of the MMF output. The model output leads to the requirements on the ATR measurement conditions and numerical aperture (NA) of the system. The model is compared to practical results of MEMS spectrometer which is experimentally characterized over the mid-infrared (MIR) wavenumber range from 5000 cm−1 to 2100 cm−1, lower limited by the used fiber and photodetector cut-off. Spectra of liquid samples are obtained using two different crystals and total internal reflection (TIR) angles showing good agreement with theoretical prediction.

Transmittance of transparent horizontal and tilted windows supporting large non-absorbing pendant droplets

This study establishes that the deviation of large pendant droplets from an ideal cap-shape due to gravity can have significant and complex impacts on the normal-hemispherical and directional-hemispherical transmittances of light through horizontal and tilted transparent windows. First, the shape of pendant droplets larger than the capillary length was predicted numerically by balancing gravitational and surface tension forces for various droplet volumes, contact angles, and window tilt angles. Then, light transfer through windows supporting such numerically generated droplets was simulated using the Monte Carlo ray-tracing method. The window transmittance for large droplets was found to be nearly independent of droplet spatial arrangement and size distribution for relatively narrow size distributions. Furthermore, the droplets could be assumed to be cap-shaped in predicting the normal-hemispherical transmittance for droplet volumes V< 10 µL and contact angles θc<θcr where θcr is the critical angle for total internal reflection at the droplet/air interface. However, for larger droplets and/or contact angles, assuming droplets to be cap-shaped caused the transmittance to be overestimated by as much as 37% for horizontal windows. This was due to gravity-induced deformation of the droplet shape resulting in increased reflection at the droplet/air interface. For tilted windows, the droplet deformation caused the normal-hemispherical transmittance to increase with increasing droplet volume and window tilt angle. For both horizontal and tilted windows, transmittance decreased linearly with increasing droplet surface area coverage. These results and numerical tools can be used to design energy efficient solar stills, greenhouses, and covered photobioreactors, for example.

Stimulated emission in vicinity of the critical angle

We have demonstrated amplified spontaneous emission (ASE) propagating along the planar interface between two adjacent dielectrics with slightly different refractive indexes. This emission originates from the leaky mode, fueled by optical gain in the low-index dielectric, that is outcoupled to the high-index dielectric in vicinity of the critical angle for total internal reflection. This led us to the observation of spectacular concentric rings of ASE emission occurring above the low and soft stimulated emission threshold. The results of our study can be used to develop novel miniature low-threshold stimulated emission sources and photonic circuits operating at optical frequencies.

Fabrication-Friendly On-Chip Silicon Polarizer Based on Polarization-Selective Corner Mirrors

We propose and demonstrate a fabrication-friendly on-chip polarizer based on polarization-selective corner mirrors. The total internal reflection angles are distinct between TE and TM modes due to the strong birefringence of silicon-on-insulator (SOI) waveguide. Thus, by properly choosing the inclination angle, TE mode can be completely reflected at each corner mirror with negligible losses, whereas TM mode can be efficiently filtered out. The minimum feature size of such polarizer is as large as 400 nm. The measurement results show low excess losses of <; 1.2 dB and high extinction ratios of >20 dB over a 200-nm bandwidth. Such high performance can be maintained even with a large width deviation of > ±50 nm.