Multilayer Dielectric Structure Research Articles

Investigation of optical properties of multilayer dielectric structures using prism-coupling technique

A method based on resonant excitation of waveguide modes with a prism coupler is proposed for measuring the thickness and refractive index of thin-film layers in multilayer dielectric structures. The peculiarities of reflection of TE- and TM-polarised light beams from a structure comprising eleven alternating layers of zinc sulfide (ZnS) and magnesium barium fluoride , whose thicknesses are much less than the wavelength of light, are investigated. Using the mathematical model developed, we have calculated the coefficients of reflection of collimated TE and TM light beams from a multilayer structure and determined the optical constants and thicknesses of the structure layers. The refractive indices of the layers, obtained for TE and TM polarisation of incident light, are in good agreement. The thicknesses of ZnS and layers, found for different polarisations, coincide with an accuracy of . Thus, we have demonstrated for the first time that the prism-coupling technique allows one to determine the optical properties of thin-film structures when the number of layers in the structure exceeds ten layers.

Hybrid transmission bands and large birefringence in hollow-core anti-resonant fibers

We identify, for the first time to our best knowledge, a new type of transmission band having hybrid resonance nature in hollow-core anti-resonant fibers (ARF). We elucidate its unique phase-locking feature of the electric field at the outermost boundary. Exploiting this hybrid band, large birefringence in the order of 10(-4) is obtained. Our analyses based on Kramer-Kronig relation and transverse field confinement interpret the link between the hybrid transmission band and the large birefringence. Guided by these analyses, an experimentally realizable polarization-maintaining ARF design is proposed by introducing multi-layered dielectric structure into a negative curvature core-surround. This multi-layered ARF possesses characteristics of low loss, broad transmission band and large birefringence simultaneously.

A Compact, Broadband Spiral Antenna With Unidirectional Circularly Polarized Radiation Patterns

A low-profile, compact spiral antenna with a broadband circularly polarized (CP) response is presented. The antenna is backed by a ground plane and has unidirectional radiation patterns over its entire frequency band of operation. This antenna is a multilayer structure composed of a center-fed modified Archimedean spiral that exploits a novel loading structure, a ring-shaped absorber, and a feed network, which includes a 180° power splitter. The loading structure possesses both inductive and capacitive characteristics, which increase the equivalent electrical length of the antenna while maintaining its maximum dimensions. The Archimedean spiral is integrated into the multilayer dielectric structure along with its differential feed network. An optimized ring-shaped absorber is used on the periphery of the antenna to reduce the ground effects on the antenna performance. The proposed antenna occupies a volume that is 89% smaller than that occupied by a conventional ground-plane-backed Archimedean spiral antenna. At its lowest frequency of operation, the antenna has electrical dimensions of 0.21λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> × 0.21λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> × 0.09λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> is the free-space wavelength at the lowest frequency of operation (0.5 GHz). Over the frequency range from 0.5 to 1.4 GHz (2.8:1), the antenna has a VSWR of 2.4:1, and it has a CP radiation pattern with an axial ratio better than 1.2 dB. Within this frequency range, the antenna has minimum and maximum realized gain values of -5.0 dBiC and 3.1 dBiC, respectively.

Omnidirectional reflector using linearly graded refractive index profile of 1D binary and ternary photonic crystal

The effect of the refractive index profile on the omnidirectional reflector (ODR) of one dimensional dielectric and semiconductor multilayer structure having linearly graded material has been simulated using transfer matrix method. The theoretical analysis shows that the proposed structure works as a perfect mirror within a certain wavelength range. These wavelength ranges can be completely controlled by the refractive index profile of a graded semiconductor layer and also observed that these wavelength ranges are also controlled by refractive index parameters. Reflectance characteristics of 1D binary and ternary photonic crystal (PC) structure have been studied. This property shows that the ODR range of structure increased when a third layer of semiconductor added in a binary photonic crystal.

Spectral barcodes by superposition of quasiperiodic refractive index profiles.

Averaging and shifting the refractive index profiles of quasiperiodic structure reveals the formation of several localized modes in the reflectivity spectrum and were used to generate different spectral barcodes. By associating the depth and wavelength of the observed resonant modes to the thickness and position of blackbars, respectively, the possibility to generate multiple codes has been shown. An experimental verification was carried out with multilayered dielectric porous silicon structures with reflectivity spectra revealing unique photonic fingerprints.

Reflection and transmission calculations in a multilayer structure with coherent, incoherent, and partially coherent interference, using the transmission line method.

A generalized transmission line method (TLM) that provides reflection and transmission calculations for a multilayer dielectric structure with coherent, partial coherent, and incoherent layers is presented. The method is deployed on two different application fields. The first application of the method concerns the thickness measurement of the individual layers of an organic light-emitting diode. By using a fitting approach between experimental spectral reflectance measurements and the corresponding TLM calculations, it is shown that the thickness of the films can be estimated. The second application of the TLM concerns the calculation of the external quantum efficiency of an organic photovoltaic with partially coherent rough interfaces between the layers. Numerical results regarding the short circuit photocurrent for different layer thicknesses and rough interfaces are provided and the performance impact of the rough interface is discussed in detail.

Dielectric Constant and Boundary Extraction Method for Double-Layered Dielectric Object for UWB Radars

Microwave ultra-wideband (UWB) radar systems are advantageous for their high-range resolution and ability to penetrate dielectric objects. Internal imaging of dielectric objects by UWB radar is a promising nondestructive method of testing aging roads and bridges and a noninvasive technique for human body examination. For these applications, we have already developed an accurate internal imaging approach based on the range points migration (RPM) method, combined with a method that efficiently estimates the dielectric constant. Although this approach accurately extracts the internal boundary, it is applicable only to highly conductive targets immersed in homogeneous dielectric media. It is not suitable for multi-layered dielectric structures such as human tissues or concrete objects. To remedy this limitation, we here propose a novel dielectric constant and boundary extraction method for double-layered materials. This new approach, which simply extends the Envelope method to boundary extraction of the inner layer, is evaluated in finite difference time domain (FDTD)-based simulations and laboratory experiments, assuming a double-layered concrete cylinder. These tests demonstrate that our proposed method accurately and simultaneously estimates the dielectric constants of both media and the layer boundaries.

A new characteristics matrix method based on conductivity and its application in the optical properties of graphene in THz frequency range

A new characteristics matrix method along with the formulas based on conductivity, which can be used to calculate the optical properties of an ultra-thin conductive composite multilayer dielectric structure, is derived for the first time as faras we know based on the electromagnetic boundary conditions Maxwell's equations required. It can be used to calculate the reflection, transmission, and absorption of light, provided that the conductivity of the conductive body is known, also it can overcom the shortcoming of the traditional transfer matrix method, i.e.it is necessary to know the permittivity and permeability of the material. By using the proposed method, the optical behavior of graphene and composite multilayer structures can be obtained in the THz frequency range.

One-way absorption of terahertz waves in rod-type and multilayer structures containing polar dielectrics

One-way absorption can be obtained at terahertz frequencies in low-profile rod-type and multilayer dielectric structures with broken spatial inversion symmetry, which contain either a rod layer or an ultrathin homogeneous layer made of a polar dielectric. Perfect absorption for one of the two opposite incidence directions and perfect reflection for the other one are observed at the edge of the polaritonic gap in a wide range of the incident angle variation, when the thickness of the entire structure is of the order of the incident wavelength. Moreover, this regime appears in a wide frequency range, in which the forward-to-backward absorption contrast is strong. The exploited mechanism is connected with the parameter adjustment that enables the location of the polaritonic gap of the polar dielectric, of which the lossy part of the structure is made, inside the stop band arising due to the periodicity of the lossless part of the structure that is made of a nondispersive dielectric. It also exploits absorption enhancement in the lossy part by backing it with the highly reflecting lossless part, which has alternating stop and pass bands.

Experiment and Theory of the Broadband Absorption by a Tapered Hyperbolic Metamaterial Array

A broadband absorber based on a tapered, alternating metal–dielectric multilayered structure was realized in the visible and IR range. The structure is fabricated by using a versatile method easily scalable to large areas by taking advantage of the line width reduction that occurs naturally in masked evaporation processes. The multilayered structure can be treated as a hyperbolic metamaterial (HMM), and the tapered structure can be regarded as a HMM waveguide with varying width. Light couples into the tapered structure most strongly at the mode cutoff position in the waveguide due to the hyperbolic dispersion and the phase matching condition. Resonant cavities are formed between the top of the tapered structure and the cutoff level, producing strong absorption peaks. These resonances are closely spaced spectrally due to the high k modes in HMM. Finally a broad absorption band is formed due to the broadening of the resonances from an array of coupled HMM tapered structures.

Solar-blind ultraviolet band-pass filter based on metal—dielectric multilayer structures

Solar-blind ultraviolet (UV) band-pass filter has significant value in many scientific, commercial, and military applications, in which the detection of weak UV signal against a strong background of solar radiation is required. In this work, a solar-blind filter is designed based on the concept of “transparent metal”. The filter consisting of Al/SiO2 multilayers could exhibit a high transmission in the solar-blind wavelength region and a wide stopband extending from near-ultraviolet to infrared wavelength range. The central wavelength, bandwidth, Q factor, and rejection ratio of the passband are numerically studied as a function of individual layer thickness and multilayer period.

Thickness and Permittivity Measurement in Multi-Layered Dielectric Structures Using Complementary Split-Ring Resonators

This paper presents a non-invasive microwave method based on a square-shaped complementary split-ring resonator (CSRR) to measure the thickness and permittivity of multilayer dielectric structures. The CSRR sensor is etched on the ground plane of a microstrip line. The change of resonance frequency depends on the thickness and permittivity of the multilayer dielectric sample below the ground plane. For resolution analysis, the resonance frequency shifts caused by a variation of permittivity (Δε = 0.01) and thickness (Δd=0.01 mm) in the detection layer were compared across various design dimensions. Sensor size optimization improved the resolution in permittivity and thickness measurement by 66% and 37%, respectively. Subsequently, the permittivity and thickness resolution was improved by 28% and 16%, respectively, by optimizing the separation of the etched CSRRs. The analysis results show that a CSRR sensor can be designed with excellent resolution in core layer permittivity changes and thickness resolution in multilayered dielectric structures.

Computational Procedure for Resonant Frequency of a Multi-Layer Dielectric Structure on the Basis of Circuit Analysis

This paper introduces a computational procedure to define the resonant frequency of a multi-layer dielectric structure on the basis of circuit analysis which allows for a simplest determination of its characteristic equation system vs. electrodynamic methods

Double Negative Optical Metamaterial with All-Dielectric Fishnet Structure

An all-dielectric fishnet metamaterial (DFM) composed of multilayer dielectric structure with periodically patterned holes is proposed to generate left-handed behavior in optical frequency region. Different from the metallic fishnet negative index metamaterial realized by coupling the neighbouring functional layers along the propagation direction, this DFM owes its simultaneous negative permeability and permittivity to the hybrid coupled resonances in the same layer. Based on this configration, a wide-band and polarization-independent negative refraction with maximum figure of merit as large as 13.85 is obtained by a silicon-based DFM at 450 nm wavelength. Simple and easy to fabricate, this concept is believed to provide an alternative route to realize high-performance negative index metamateirals at optical frequencies.

Diffraction of Cylindrical Waves by a Plane-Stratified Structure with a Cylindrical Inclusion

We consider the problem of radiation from an electric-current filament located near the surface of a multilayer plane dielectric structure with a cylindrical inclusion. It is assumed that the penetrable inclusion lies completely within one of the layers and its generatrices are parallel to the current filament. The solution is obtained using the modified zero-field method. The results of numerical simulation and their physical analysis are presented.

Research about Jet Flow Mechanism and Flow Field Analysis for Layered Composite Materials

Layered carbon fiber composite performing microstructure was a part of multi-layer porous piping dielectric structure. At first a jet mechanism was put forward and researched for layered composite materials. The Z reinforcing fibers puncture was put to the layered composite structures. By the CFD simulation analysis, the feasibility of jet puncture was verified, the interlayer strength of the connection was increased and the Z bunch to the carbon fiber was eliminated, which laid theoretical foundation by enhancing the layered carbon fiber composite perform quality.

Volume integral equation for analysis of three-dimensional scattering from dielectric frequency-selective structures

The space-domain volume integral equation method is presented for the analysis of three-dimension scattering from dielectric frequency-selective structures involving homogeneous and inhomogeneous lossy materials. The method directly solves for the electric field in order to easily enable the periodic boundary conditions in the spatial domain. The special basis and test functions are introduced to deal with the current continuity in periodic boundaries. The computation of the spatial domain periodic Green’s function (PGF) is accelerated by the modified Ewald transformation, so that a very thick periodic structure can also be analyzed efficiently and accurately. The PGF mentioned above is of free-space type and very smooth and amenable to interpolation. Thus, optimized interpolation procedures for the PGFs can be applied, resulting in a considerable reduction of matrix-filling time without any significant influence on the accuracy. A study of the scattering parameters of a multilayered dielectric periodic structure is accomplished by imposing the boundary conditions in terms of the multimode scattering matrix. Numerical examples show the reliability and accuracy of the proposed method.

Controlling the optical properties of composite multilayered photonic structures: effect of superposition

Tunability of the optical response of multilayered photonic structures has been compared with sequential (SQ) and superposition (SP) addition of refractive index profile functions. The optical response of the composite multilayered structure, formed after the SP addition of the two Bragg type refractive index profile functions has been studied as a function of percentage overlap and relative shift between the profiles. Apart from the substantial advantage in terms of the reduced physical thickness of the SP composite structures (over the SQ addition), at certain optimum values of relative shift, photonic structures with better quality factor resonant modes or a broader PBG could be designed. Similar analysis has been extended for rugate filters as well. The experimental verification of the optical response, was carried out through multilayered dielectric porous silicon structures fabricated by electrochemical anodization.

Optical transmittance of a multilayer structure with Gaussian modulation of the refractive index

Using the transfer matrix method we calculate the electromagnetic transmittance for a multilayer dielectric structure, where the refractive index of the layers with odd numbering follows a Gaussian distribution of values, while the inserted even layers have a constant refractive index. The transmission spectrum presents intervals of stopbands and very flat passbands.

Colored solar selective absorbing coatings with metal Ti and dielectric AlN multilayer structure

The colored solar–thermal collectors have the advantages of architectural integration and color appearance. The solar selective absorbing coatings with a metal–dielectric multilayer structure can show different colors by changing the layer number and thickness. In this work, five colored coatings with a metal titanium (Ti) and dielectric aluminum nitride (AlN) multilayer structure were designed by the optical multilayer software and fabricated by magnetron sputtering. The color of the five coatings is black, purple, yellowish green, red, and yellowish orange. The energy performance, chromaticity, and brightness of the coatings were studied and compared. The results show that the solar absorbance of these coatings is between 0.82 and 0.94, the thermal emittance is between 0.05 and 0.27, and the brightness is in the range of 0.65–8.89%. These colored coatings can be produced by a commercial production process, and is suitable for the application of building integration.