Oblique Incidence Of Light Research Articles

Polarization rotation of localized modes in magneto-photonic Fibonacci structures containing nematic layers

ABSTRACTIn this study, we investigate the spectral characteristics of the oblique incident light transmitted by a multilayered structure composed of a quasi-periodic Fibonaccian sequence of nematic and magnetic layers. Using the Berreman 4 × 4 matrix formalism, we numerically obtain the transmission spectrum and the polarization rotation angle of the system as a function of the incidence angle. Our results reveal that the mismatch between the wavelengths of the localized transmitted mode within the band gap and the mode with pronounced polarization rotation angle is reduced when one departs from the normal incidence condition. Further, we report the dependence of the band gap width and the spectral characteristics of the transmitted mode as a function of the incidence angle. The relevance of the present finding to the development of new magneto-optical devices is discussed.

New regions of diffraction reflection in apodized one-dimensional photonic crystals with a large modulation depth

Particular features of the band structure of one-dimensional apodized photonic crystals based on metamaterials are studied in the case in which the medium is simultaneously inhomogeneous with respect to both the dielectric and the magnetic properties. It is shown that in the case of oblique incidence of light at large values of the modulation depth, a new region of diffraction reflection appears. This new region of diffraction reflection is also observed at magnetic permeability μ = const = 1. The particular features of the absorption and localization of light in these structures are examined.

Extrinsic chirality of non-concentric plasmonic nanorings

We show how extrinsic chirality, i.e. the optical activity of achiral media exhibited at oblique light incidence, can be achieved in plasmonic nanorings by symmetry breaking. We demonstrate that even a small, 5% offset of an inner hole of a 190 nm gold ring results in a measurable circular dichroism signal in the near-infrared region. By using computer simulations, we show that optical activity arises upon excitation of a symmetric dipolar localized surface plasmon resonance mode due to the appearance of co-aligned electric and magnetic dipole moments.

Optical Tamm states at the interface between a photonic crystal and a gyroid layer

The spectral properties of a one-dimensional photonic crystal bounded by an absorbing plasmonic gyroid layer are investigated. The gyroid material is a foam-like metallic three-dimensionally periodic curved film with zero mean curvature at every point. We calculate the transmittance and reflectance spectra at the normal and oblique light incidence. The possibility of the Tamm state formation at the interface between a photonic crystal and a plasmonic gyroid layer caused by the negative real part of the gyroid permittivity is demonstrated for the first time. Specific features of field localization at the Tamm state frequencies are discussed. It is shown that the spectral and polarization properties of the optical Tamm states are highly sensitive to the change in the angle of incidence and in the refractive index of a medium filling the gyroid cavities.

Light diffraction features in an ordered monolayer of spheres

The structure and optical diffraction properties of monolayers of monodisperse spheres crystallized on transparent dielectric substrates are studied. Two types of diffraction phenomena are considered: surface light diffraction on the lattice of spheres and waveguide resonances in the monolayer plane. For experimental study of these phenomena, optical retroreflection and transmission spectra are measured as functions of the light incidence angle and azimuthal orientation of the incidence plane. The monolayer structures determined by scanning electron microscopy and light diffraction methods are in quantitative agreement. It is concluded that one-dimensional Fraunhofer diffraction is applicable to describe surface diffraction in the hexagonal lattice of spheres. In the case of oblique light incidence, anisotropy of diffraction and transmission spectra depending on the light incidence plane orientation with respect to the sphere lattice and linear polarization of incident light is detected. Waveguide resonances of the planar two-dimensional photonic crystal are approximated within the light diffraction model in the “empty” hexagonal lattice. The best approximation of the waveguide resonance dispersion is achieved using the effective refractive index, depending on the wavelength. Surface diffraction suppression by waveguide resonances of the photonic crystal is demonstrated. Surface diffraction orders are identified as diffraction at singular points of the Brillouin zone of the planar twodimensional photonic crystal.

Bragg reflection from periodic helicoidal media with laterally graded refractive index

Light interaction with a columnar structure of InxAl1-xN where each column is a layered periodic helical medium with laterally graded refractive index is considered. It is demonstrated that such a columnar structure can be presented as a stack of layers with a gradient of the refractive index. To calculate reflectance in the proposed model, the 2 × 2 characteristic matrix method adopted for a gradient index medium was applied. The influence of the refractive indices (including absorption), parameters of the twisting, and thickness of the periodic structure on reflectance is studied. Cases of normal and oblique incident light are considered. The presented medium is a one-dimensional photonic crystal that can be utilized in many devices for light manipulation.

Thermal analysis on multijunction photovoltaic cell under oblique incident laser irradiation

Laser beam irradiation was modeled to investigate the thermal responses of multijunction photovoltaic cell to the irradiation of oblique incident monochromatic light. First, the monochromatic light absorption in multijunction photovoltaic cell is formulated with accounting for multiple reflections as well as interferences. Then, an iterative algorithm was established to calculate the depositions of incident laser energy in every layer. Finally, the temperature characteristics of the photovoltaic cell are analyzed with finite element method.

Effect of angle of incidence on the performance of bulk heterojunction organic solar cells: A unified optoelectronic analytical framework

We analyze the performance of bulk heterojunction organic solar cells under oblique incidence of light. In this regard, we present an optoelectronic analytical model that describes the current-voltage characteristics of bulk heterojunction organic solar cells taking into account the effect of angle of incidence. A closed-form general expression is derived for the optical generation rate under oblique incidence employing transfer matrix formalism. The resulting expression is then incorporated in the classical drift-diffusion transport and continuity equations of charge carriers to derive a unified expression of voltage dependent current density combining optical and electrical parameters. Thus, the model is capable of determining the accurate optical absorption in the active layer for varying angles of incidence as well as predicting the corresponding wavelength dependent external quantum efficiency of the device. The results are verified by comparing with published numerical and experimental results. We show that the maximum efficiency might be achieved at an oblique angle of incidence rather than normal incidence for certain active layer thicknesses. We also report the optimum angles at which the maximum efficiency occurs and show that they are active layer thickness dependent.

Band structure peculiarities of magnetic photonic crystals

In this work we studied light diffraction in magneto-photonic crystals (MPC) having large magneto-optical activity and modulation large depth. The case of arbitrary angles between the direction of the external static magnetic field and the normal to the border of the MPC layer is considered. The problem is solved by Ambartsumian’s modified layer addition method. It is found that there is a new type of non-reciprocity, namely, the relation R(α)≠R(-α) takes place, where R is the reflection coefficient, and α is the incidence angle. It is shown the formation of new photonic band gap (PBG) at oblique incidence of light, which is not selective for the polarization of the incident light, in the case when the external magnetic field is directed along the medium axis. Such a system can be used as: a tunable polarization filter, polarization mirror, circular (elliptical) polarizer, tunable optical diode, etc.

Manifestation of optical activity at oblique incidence of light in crystals of classes $$\overline 4 $$ 4 ¯ 2m and $$\overline 4 $$ 4 ¯

The polarization azimuths and ellipticities of the reflected and transmitted light have been calculated as functions of the angle of incidence for transparent crystals of classes \(\overline 4 \)2m and \(\overline 4 \). Analytical expressions for these parameters are obtained. It is shown that in the general case the polarization azimuths and ellipticities for a plate cut parallel to the optical axis differ for positive and negative angles of incidence of light.

Optical chirality of achiral three-dimensional photonic crystals

Extrinsic optical chirality in a form of the asymmetric transmission of circularly polarized light at the oblique light incidence has been observed in three-dimensional opal photonic crystals assembled from monodisperse polymer spheres in the closely packed face-centered-cubic lattice. This effect has been assigned to the translation-rotation symmetry of the lattice. The cross-polarization conversion of the circularly polarized light and the related asymmetry of the transmission of the inverted circularly polarized light have been demonstrated.

Circular Dichroism in Planar Achiral Plasmonic L-Shaped Nanostructure Arrays

Circular dichroism (CD) can be initially observed in intrinsic chiral structures. It was discovered that CD can also be observed in achiral structures with an oblique incident light beam. In this paper, a metal planar achiral L-shaped nanostructure arrays was proposed, and its CD was investigated using the finite element method. The CD phenomenon is due to extrinsic chirality resulting from the achiral structures with an oblique incident electromagnetic wave. Results show that the L-shaped nanostructure arrays can achieve strong and broad bandwidth CD. In addition, the sign of CD can be reversed through changing azimuthal rotation angle of incident light, and the strength of CD depends strongly on light incident direction.

Effects of cell gap on the optoelectronic properties of pure blue-phase liquid crystal devices: estimating the Kerr constant.

In this study, the Kerr constant of pure blue-phase liquid crystal (BPLC) without polymer doping at room temperature and the optoelectronic properties dependent on the cell thickness are explored. The relation between the phase and the voltage in oblique incident light was measured via a reasonable vertical electric field for different thicknesses of BPLC cells. It was found that the Kerr constant formula can be amended with the functions related to the cell gap. This study demonstrates a method to estimate the Kerr constant, especially for cells within a small electrical field, which will benefit optoelectronic applications.

Enhanced circular photogalvanic effect in HgTe quantum wells in the heavily inverted regime

Thanks to the strong spin-orbit interaction (SOI), HgTe-based quantum wells (QWs) exhibit very rich spin-related properties. But the full descriptions of them are beyond the simple parabolic band models and conventional Rashba and Dresselhaus SOI terms, as a result of the strong interband coupling of the narrow gap band structures. Here, we develop a theoretical method to calculate the circular photogalvanic effect (CPGE) in Hg$_{0.3}$Cd$_{0.7}$Te/HgTe/Hg$_{0.3}$Cd$_{0.7}$Te quantum wells (HgTe QWs) based on the realistic eight-band $\mathbf{k}\cdot\mathbf{p}$ model with density matrix formalism. Our method could take account of the unusual band structures and SOIs of HgTe QWs, therefore can be used to calculate the CPGE currents in HgTe QWs with non-parabolic, Dirac-like and inverted energy dispersions. The microscopic origin of CPGE and the interplay effect of structure inversion asymmetry (SIA) and bulk inversion asymmetry (BIA) is also investigated. In addition, this method is extended to study the pure spin currents (PSCs) in HgTe QWs injected by linearly polarized light at normal incidence. Our calculation results support the following findings: (i) In the inverted phase regime, the energy dispersion of heavily inverted HgTe QWs could be strongly distorted, lead to a significant enhancement of CPGE at a certain range of energy spectrum. (ii) The interplay of SIA and BIA could lead to the CPGE currents anisotropically dependent on the azimuth angle of oblique incident light. (iii) The PSC $j_{y'}^{x'}$ ($x'\parallel[110]$ and $y'\parallel[\bar{1}10]$) produced by [110]-linearly-polarized light could change sign with HgTe QW transformed from normal phase to inverted phase. These findings might be utilized in developing the HgTe-based infrared/terahertz optoelectronic and spintronic devices.

Considering Symmetry Properties of InP Nanowire/Light Incidence Systems to Gain Broadband Absorption

Geometrically designed III-V nanowire arrays are promising candidates for disruptive optoelectronics due to the possibility of obtaining a strongly enhanced absorption resulting from nanophotonic resonance effects. With normally incident light on such vertical nanowire arrays, the absorption spectra exhibit peaks that originate from excitation of HE1m waveguide modes in the constituent nanowires. However, the absorption spectra typically show dips between the absorption peaks. Conventionally, such weak absorption has been counteracted by either making the nanowires longer or by decreasing the pitch of the array, both alternatives effectively increasing the volume of absorbing material in the array. Here, we first study two approaches for compensating the absorption dips by exciting additional Mie resonances: 1) oblique light incidence on vertical InP nanowire arrays and 2) normal light incidence on inclined InP nanowire arrays. We then show that branched nanowires offer a novel route to achieve broadband absorption by taking advantage of simultaneous excitations of Mie resonances in the branches and guided HE1m modes in the stem. Finite element method calculations show that the absorption efficiency is enhanced from 0.72 for vertical nanowires to 0.78 for branched nanowires under normal light incidence. Our work provides new insight for the development of novel efficient photovoltaics with high efficiency and reduced active material volume.

Observation of Dynamic Wetting Behavior by Fringe Method with Bottom Up Oblique Incident Light

Observation of Dynamic Wetting Behavior by Fringe Method with Bottom Up Oblique Incident Light

可視域から近赤外域にわたる広帯域および広角入射光を制御する多層フィルム構造の最適設計

The purpose of this study is to obtain an optimum structure by using the optimum design method of multi-layered films under the target specifications to reflect the near-infrared light range and transmit the visible light range. We propose a method to achieve the spectral characteristics of the target specification in a wide wavelength range by combining substructures to high reflection of light. In this study, a sub-structure to control the oblique incident light at a particular angle is formulated and applied to design of multilayered structure. It works not only for vertical incident light but also for oblique incident light. Furthermore the film structure is designed for controlling more wide range of oblique incident angle by laminating the resulting sub-structures. Finally multilayer films that achieved high reflection in the near infrared region for wide-angle incident light are obtained. We investigated a method of improving the transmittance for light of wavelength in the visible range that contribute to power generation of solar panels using the multi-objective optimization method.

Experimental investigation on aero-optics of supersonic turbulent boundary layers at different light incident angles

The aero-optical distortion caused by the compressibility of high-speed flow field has a great influence on the development of airborne optical detection system of (hypersonic) supersonic vehicles. The turbulent boundary layer is one of the most important aspects in the aero-optical study, and has become one of the hot research points in the field of aero-optical study. The nano-particle-based planar laser scattering technique is used to measure the density distribution of the supersonic (Ma=3.0) turbulent boundary layers, and the optical path difference, which is quite crucial for the aero-optical study, is obtained by ray-tracing method. The experimental result is verified by being compared with the theoretical result computed by the aero-optical scaling method of turbulent boundary layers. Five different light incident angles (α=60°, 75°, 90°, 105°, 120°) are selected and used to examine the influences of light incident angles on the supersonic turbulent layer, and the underlying flow physics is analyzed. Research shows that the light propagation path in the supersonic turbulent boundary layer contributes to the light incident angle dependence of aero-optics. The different propagation paths lead to the difference between the light propagation distance in the flow field and the correlation results of the corresponding density fluctuation. The oblique incidence of light results in the increase of the propagation distance in the flow field, and then the aero-optics turns worse. The greater the angle between the incident direction of light and the vertical direction of the wall, the more significant the aero-optics is, the difference increases at different times, the difficulty in correcting the aero-optics is also increased. In the supersonic turbulent boundary layer, a large number of vortices with a specific orientation lead to the anisotropy of the aero-optics in the turbulent boundary layer. By calculating the spatial two-point correlation of the density fluctuations at the streamwise plane (x-y plane), the cross-correlation result of density fluctuations at any light incidence angle (α=0°-180°) can be obtained. The local coherent structure scale is nearly 0.20 mm, which is basically consistent with the aero-optical effective scale (≈ 0.18 mm) computed from the formula proposed by Mani et al. When the light is inclined downstream, the direction of light propagation is consistent with the vortex structure in the flow field, and in this direction, the correlation coefficient of density fluctuation is larger, so the aero-optics is more serious. When the light beam is tilted upstream, the correlation coefficient is smaller, so the aero-optics is weaker.

Optical anisotropy of cubic photonic crystals under conditions of multiple-mode light propagation

Bragg reflection spectra of light are studied for opal-like photonic crystals made of polystyrene spheres. A resonant enhancement of reflectivity is observed in cross-polarization configuration of the analyzer and polarizer when varying the azimuthal orientation of a sample in respect to the incidence plane. The cross-polarization effect takes place at oblique incidence of light on the lateral (111) crystal plane with the plane of incidence being non-perpendicular to the inclined (11-1) crystal plane. The effect is shown to be due to the multiple Bragg diffraction of light when the resonant Bragg conditions are fulfilled at a certain angle of incidence and azimuth for the lateral and inclined crystal planes simultaneously.

Unidirectional Coupling of Surface Plasmon Polaritons by a Single Slit on a Metal Substrate

In this letter, a theoretical model is proposed to calculate the coupling efficiency of surface plasmon polaritons (SPPs) by a single slit on the metal film. In contrast to previous work developed for normal incident light only, TM0 and TM1 modes of the slit are incorporated in the model, which makes it applicable for the case of oblique incidence. Numerical simulations confirm that this two-mode model can accurately predict the coupling efficiency of SPPs by slits with subwavelength widths ( $ ). Moreover, we demonstrate that unidirectional SPPs can be coupled by an oblique incident light beam, which can be explained by the generation and interference of these two modes in the slit.