Scattering properties of metallic carbon nanotubes in the presence of dielectric media

Scattering properties of a metallic single-walled carbon nanotube that encapsulates a nanowire is studied within the framework of classical electrodynamics. The system is assumed to be illuminated by either a transverse magnetic (TM) or a transverse electric (TE) wave. Electronic excitations on the nanotube's surface are modeled as an infinitesimally thin cylindrical layer of the π-electrons, whose dynamics are described by means of the fluid hydrodynamic theory. The problem is two-dimensional and the solution to both TM and TE uniform plane waves by the system at normal incidences is presented.     

Analysis of the focal characteristics of cylindrical lenses made of anisotropically dielectric material based on rigorous electromagnetic theory

Abstract

The focal characteristics of refractive cylindrical lenses made of anisotropically dielectric material (uniaxial crystal) are analysed based on rigorous electromagnetic theory and the boundary element method. The performances of the lenses with different f numbers are appraised for both incident waves of the TE (transverse electric) and TM (transverse magnetic) polarizations. Numerical results show that the focal performance of this kind of lens for the TE polarization and the TM polarization of incident light wave is a difference, in particular, different focal lengths, owing to the anisotropy of the material. However, for the conventional isotropic lens, the focal features for both the TE and TM polarizations are the same. It is anticipated that this new kind of lens proposed for the first time may serve as a light switching device with high speed used in the micro-optical communication.     

Polarization dependent solar cell conversion efficiency at oblique incident angles and the corresponding improvement using surface nanoparticle coating

Despite tremendous efforts on improving the solar cell conversion efficiency at normal incidence, improvement at oblique angles has not been widely addressed, not to mention the corresponding light absorption behaviors at different polarizations. Here we report the characterization of the solar cell conversion efficiency and the spectra of photoresponsivity at various tilted angles. The results show that TM (transverse magnetic) polarized light possesses higher photoresponsivity than TE (transverse electric) polarized light and the difference becomes larger with the incidence angle. To address the issue, a monolayer of silica nanoparticles on the solar cell surface was employed to improve the light absorption. Even though both TE and TM waves show a decrease in the surface reflectivity with the presence of nanoparticles, the interaction between the silica particles and the TE wave is more significant. The improvement of the conversion efficiency for obliquely incident light is explained from the refractive index difference of the nanoparticles for the TE and TM polarizations.     

Analysis of Reflectance Properties in 1D Photonic Crystal Containing Metamaterial and High-Temperature Superconductor

In the present work, reflectance properties of one-dimensional photonic crystal (1D PC) containing a metamaterial and high-temperature superconductor have been investigated theoretically and analyzed. The reflectance/transmittance spectrum of the proposed structure is obtained by using the characteristic or transfer-matrix method (TMM). The results show that by increasing the thickness of the metamaterial layer, the width of the second reflection band decreases while the width of the first reflection band remains almost the same though it shifts towards the higher frequency side. In addition to this, a new band gap arises in the lower side of frequency. But, when the thickness of the superconductor layer is increased, the width of both the bands increases and no additional band arises in this case. Moreover, the reflection band is also affected by varying the operating temperature of the superconducting layer and the results show that bands get narrower by increasing the operating temperature. Finally, the effect of incident angle on the reflection band has been discussed for both transverse electric (TE) and transverse magnetic (TM) polarizations.     

Investigation of Reflectance Properties in 1D Ternary Annular Photonic Crystal Containing Semiconductor and High-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Bold">c</Emphasis></Subscript> Superconductor

In this paper, we present the theoretical investigation and study of reflectance properties in a 1D ternary annular photonic crystal (TAPC) containing a semiconductor and a high-temperature superconductor. The proposed structure consists of alternate layers of indium nitride (InN), Bi₂Sr₂CaCu₃O₈ (BSCCO), and air placed in free space. A reflectance spectrum of the TAPC is obtained by employing the transfer matrix method (TMM) in the cylindrical waves for both transverse electric (TE) and transverse magnetic (TM) polarized waves. From the study of reflectance spectra, it is observed that the reflection band of the annular photonic crystal depends on the azimuthal mode number m in addition to other parameters. It is found that for azimuthal mode number m = 0, the width of the reflection band of the annular photonic crystal is the same as that of a planar photonic crystal (PPC). When the azimuthal mode number increases, the width of the reflection band increases at higher m values (m >5) for TE waves. In the case of the TM wave, it is interesting to observe that a superpolariton gap is created for a higher value of the azimuthal number (m >0). Further, we see the effect of the starting radius (ρ ₀) on the reflection band of the TAPC structure at the given m number for both TE- and TM-polarized waves. Finally, the effect of temperature on the reflectance spectra for both TE and TM waves at the given ρ ₀ and azimuthal mode has been studied.     

Light propagation along periodic metal-dielectric layers

Analysis and experiments on TE and TM waves along periodically laminated metal-dielectric layers are described; the waves propagate parallel to the layers. Aluminum (Al) and silica (SiO2) are chosen as the metal and the dielectric, respectively. We find that the attenuation for TE waves is much higher than that for TM waves. Typically, alphaTE/alphaTM ranges from 10(3) to 10(4). Thus, an optical polarizer can be made in a multilayer structure.     

Critical Angles for Reflectivity at an Isotropic-anisotropic Boundary

Abstract

The angular dependent reflectivities, and in particular sharp, critical, edges in these have been analysed for the boundary between an isotropic and a uniaxial medium. For the general uniaxial case, it is shown that for measured reflectivities of the type transverse magnetic (TM) incident to TM reflected or transverse electric (TE) incident to TE reflected there is only one sharp critical angle, the other being rounded due to TM to TE conversion. On the other hand if the TM to TE conversion reflectivity is measured (or TE to TM) then a sharp cusp occurs at the otherwise rounded critical edge. This thereby allows, from some very simple reflectivity measurements the determination of the optical tensor for the anisotropic medium. A full analytic treatment of this behaviour is presented together with numerical evaluations of the electromagnetic field distributions which illustrate how this cusp arises. The possible application of the use of this TE to TM conversion cusp measurement in the case of obliquely oriented liquid crystals is also discussed.     

Transformation properties of an indefinite media slab for paraxial beams

On the basis of paraxial beam propagation theory in indefinite media, the effective refraction index for both of the two types of polarized electromagnetic wave, TE and TM waves, are introduced. According to the definition of effective refraction index, we obtain the conditions that paraxial beams pass through the indefinite media. We propose to employ a slab of indefinite media to construct a polarizer or polarizing beam splitter by choosing appropriate anisotropic parameters. Under certain conditions, the indefinite media slab exhibits polarization-selective focusing effect.     

Spatially resolved plasmonically enhanced photocurrent from Au nanoparticles on a Si nanowire

Semiconducting nanowires have been demonstrated as promising light-harvesting units with enhanced absorption compared to bulk films of equivalent volume. However, for small diameter nanowires, the ultrahigh aspect ratio constrains the absorption to be polarization selective by responding primarily to the transverse magnetic (TM) light. While this effect is useful for polarization-sensitive optoelectronic devices, practical light-harvesting applications demand efficient light absorption in both TM and transverse electric (TE) light. In this study, we engineer the polarization sensitivity and the charge carrier generation in a 50 nm Si nanowire by decorating the surface with plasmonic Au nanoparticles. Using scanning photocurrent microscopy (SPCM) with a tunable wavelength laser, we spatially and spectrally resolve the local enhancement in the TE photocurrent resulting from the plasmonic near-field response of individual nanoparticles and the broad-band enhancement due to surface-enhanced absorption. These results provide guidance to the development and the optimization of nanowire-nanoparticle light-harvesting systems.     

Tunable Modal Birefringence in a Low‐Loss Van Der Waals Waveguide

van der Waals (vdW) crystals are promising candidates for integrated phase retardation applications due to their large optical birefringence. Among the two major types of vdW materials, the hyperbolic vdW crystals are inherently inadequate for optical retardation applications since the supported polaritonic modes are exclusively transverse‐magnetic (TM) polarized and relatively lossy. Elliptic vdW crystals, on the other hand, represent a superior choice. For example, molybdenum disulfide (MoS₂) is a natural uniaxial vdW crystal with extreme elliptic anisotropy in the frequency range of optical communication. Both transverse‐electric (TE) polarized ordinary and TM polarized extraordinary waveguide modes can be supported in MoS₂ microcrystals with suitable thicknesses. In this work, low‐loss transmission of these guided modes is demonstrated with nano‐optical imaging at the near‐infrared (NIR) wavelength (1530 nm). More importantly, by combining theoretical calculations and NIR nanoimaging, the modal birefringence between the orthogonally polarized TE and TM modes is shown to be tunable in both sign and magnitude via varying the thickness of the MoS₂ microcrystal. This tunability represents a unique new opportunity to control the polarization behavior of photons with vdW materials.     

A photoexcited switchable perfect metamaterial absorber/reflector with polarization-independent and wide-angle for terahertz waves

We present a photoexcited switchable perfect metamaterial absorber/reflector for terahertz waves. The switchable absorber/reflector is based on a cross-shaped structure (CSS) integrated semiconductor photoconductive silicon (Si). The electric response property of the photoconductive Si can be easily modified through a pump optical beam. The conductivity of Si pads filled in the gap of CSS is tuned efficiently through the incident pump optical beam with different power, resulting in the modulation of absorption magnitude from 0 to 100% at the fixed operation frequency. Thus, the switch ability of the perfect absorber/reflector can be easily realized. Furthermore, the proposed design is polarization insensitive and operated well at wide incidence angles for both TE and TM waves.     

Dispersion relation of guided-mode resonances in multimode grating waveguide structures

It is well known that the location of guided-mode resonance (GMR) in grating waveguide structures closely tracks the leaky mode dispersion curves. In this paper, taking Bragg reflection due to periodicity and interaction between different modes into account, we first present a schematic diagram of the dispersion relations of leaky modes in multimode grating waveguide structures, both for s-polarized (TE mode) and p-polarized (TM mode) incident waves. Due to the perturbation of the grating layer, the interaction between different resonance modes (transverse standing waves) is inevitable. This transverse interference will result in the non-Bragg nature resonance band gaps in the dispersion curves. Exploiting the characteristics of leaky mode dispersions over the full range of the first Brillouin zone, we hoped we could gain some insight into the relationship among the mode interactions, band gaps, and their benefits to optical elements utilizing the GMR effect in grating waveguide structures. Finally, a specific structure is analyzed.     

Resonant scattering of light from a glass/Ag/MgF2/air system with rough interfaces and supporting guided modes in attenuated total reflection

We report experimental results of the resonant scattering of light from a prism-glass/Ag/MgF2/air system with use of the attenuated total reflection technique for p and s polarized light. Two MgF2 film thicknesses were used. The system with the thinner dielectric layer supports two transverse magnetic (TM) and two transverse electric (TE) guided modes at a wavelength of 632.8 nm, and the system with the thicker dielectric layer supports three TM and three TE guided modes. In both cases we found dips in the specular reflection as a function of incident angle that is due to excitation of guided modes in the MgF2 film. The scattered light shows peaks at angles corresponding to the measured excitation of the guided modes. These peaks are due to single-order scattering and occur for any angle of the incident light. All features in the scattering response are enhanced in resonance conditions, and the efficiency of injecting light into the guide is reduced.     

Design of retrodiffraction gratings for polarization-insensitive and polarization-sensitive characteristics by using the Taguchi method

We present the design of retrodiffraction gratings that utilize total internal reflection (TIR) in a lamellar configuration to achieve high performance for both TE and TM polarized light and polarization-sensitive performance for gratings behaving as polarizer filters; the design was based on rigorous coupled wave analysis (RCWA) and the Taguchi method. The components can thus be fabricated from a single dielectric material and do not have to be coated with a metallic or dielectric film layer to enhance the reflectance. The effects of the structural and optical parameters of lamellar gratings were investigated, and the TIR gratings in a lamellar configuration were structurally and optically optimized in terms of the signal-to-noise ratio (S/N) and a statistical analysis of variance (ANOVA) of the refractive index, grating period, filling factor, and grating depth as control factors and the estimated efficiency by RCWA as a noise factor. For more accurate robustness, a two-step optimization process was used for each purpose. For TIR gratings designed to perform similarly for TE and TM incident polarization, the -1st-order efficiencies were estimated to be up to 92.0% and 88.5% for TE and TM polarization, respectively. Also, for the TIR gratings designed to achieve polarization-sensitive performance when behaving as a polarizer filters, the -1st-order diffraction efficiencies for TE and TM polarization were estimated to be up to 95.5% and 2.7%, respectively. From these analysis results, it was confirmed that the Taguchi method shows feasibility for an optimization approach to a technique for designing optical devices.     

YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript>/BaTiO<Subscript>3</Subscript> 1D Superconducting Photonic Crystal with Tunable Broadband Response in the Visible Range

Based on the transfer matrix method, we studied theoretically the transmittance of a 1D photonic crystal (PC), consisting of alternating layers of a dielectric material (BaTiO₃) and a superconductor (YBa₂Cu₃O_7?x ). The dielectric properties of this system are described by the two fluid model. We have investigated the transmittance intensity and its bandwidth dependence on the superconductor thickness, incident angle, and temperature in the PC. It was found that the electromagnetic wave propagation can be controlled to be forbidden or allowed in certain wavelengths in the visible and ultraviolet range, and the photonic band gap (PBG) width can also be tuned varying these parameters. We showed that by increasing the thickness of the superconductor layer it is possible to control the number of PBGs in the structure. Also, we found that the frequency ranges of PBGs are sensitive to the incident angle and the polarization of the electromagnetic waves; the bandwidth of PBGs can be notably enlarged by increasing the angle in the TE polarization, but narrowed in the TM one. Additionally, we found that transmission is not markedly affected by temperature variation, but small shifts in the PBGs are presented. We hope these results can be of technical use for developing potential applications in optoelectronic devices.     

Compact hybrid TM-pass polarizer for silicon-on-insulator platform

Hybrid waveguides consisting of a metal plane separated from a high-index medium by a low-index spacer have recently attracted a lot of interest. TM and TE modes are guided in two different layers in these structures and their properties can be controlled in different manners by changing the waveguide dimensions and material properties. We examine the effects of different parameters on the characteristics of the two modes in such structures. We show that by properly choosing the dimensions, it is possible to cut off the TE mode while the TM mode can still be guided in a well-confined manner. Using this property of the hybrid guide, we propose a TM-pass polarizer. The proposed device is very compact and compatible with the silicon-on-insulator platform. Finite-difference time-domain simulation indicates that such a polarizer can provide a high extinction of the TE mode for a reasonable insertion loss of the TM mode.     

Tin-diffused glass slab waveguides locally covered with tapered thin TiO2 films for application as a polarimetric interference sensor with an improved performance

Common soda lime slide glass substrates made by floating molten glass on the surface of molten tin contain a tin-diffused layer that is demonstrated to be a low-loss polarization-insensitive slab optical waveguide. In this study, such a tin-diffused waveguide was locally covered with a tapered thin TiO2 film to form a composite structure in which the zeroth-order transverse electric (TE0) and magnetic (TM0) modes are spatially separated from each other. This feature enables the composite structure to serve as a highly sensitive polarimetric interferometer. Moreover, a negligible modal birefringence of tin-diffused waveguides offers the polarimetric interferometer an improved performance relative to those fabricated earlier using single-mode potassium ion-exchanged glass waveguides. In situ detection of both the protein adsorption and a small change in refractive index of liquid was accomplished using the tin-diffused waveguide-based polarimetric interferometer. With horse heart myoglobin, adsorption from aqueous solution less than 0.125 monolayer coverage can cause the interferometer to yield a phase-difference change of delta phi = 2pi.     

A polarization-independent and broadband microwave metamaterial absorber based on three-dimensional structure

In this paper, we design a polarization-independent and broadband microwave metamaterial absorber (MMA) based on three-dimensional structure. The simulated results show that the proposed absorber has a broad absorptance band from 60.4 to 100.0 GHz with the absorptance efficiency over 90%. The effective medium theory (EMT), electric field, surface current and power loss density distributions are adopted to explain the physical mechanism of the perfect absorptance. In addition, the absorptance differences can be observed between transverse electric (TE) wave and transverse magnetic (TM) wave at oblique incidence. The proposed absorber can be utilized in many applications such as perfect absorbers and radomes.     

Reflection and refraction of an arbitrary electromagnetic wave at a plane interface separating an isotropic and a biaxial medium.

Exact solutions are obtained for the reflected and transmitted fields resulting when an arbitrary electromagnetic field is incident on a plane interface separating an isotropic medium and a biaxially anisotropic medium in which one of the principal axes is along the interface normal. From our exact solutions for the reflected fields resulting when a plane TE or TM wave is incident on the plane interface, it can be inferred that the reflected field contains both a TE and a TM component. This gives a change in polarization that can be utilized to determine the properties of the biaxial medium. The time-harmonic solution for the reflected field is in the form of two quadruple integrals, one of which is a superposition of plane waves polarized perpendicular to the plane of incidence and the other a superposition of plane waves polarized parallel to the plane of incidence. The time-harmonic solution for the transmitted field is also in the form of two quadruple integrals. Each of these is a superposition of extraordinary plane waves with displacement vectors that are perpendicular to the direction of phase propagation.     

Accurate modeling of dielectric interfaces by the effective permittivities for the fourth-order symplectic finite-difference time-domain method

The fourth-order finite-difference time-domain (FDTD) method using a symplectic integrator propagator can calculate the propagation of the electromagnetic waves with very low dispersion error in the region of a constant or smoothly varying index profile. An additional technique is required for the problem with the discontinuous dielectric interfaces. We derived the third-order effective permittivities at dielectric interfaces for the fourth-order FDTD method in the case of 2D TE polarization. As the required accuracy level is increased, the memory resources used by the fourth-order FDTD method with the effective permittivities are reduced severalfold or more compared with the standard FDTD method. The accurate performance of the proposed method is demonstrated through numerical examples.