Electric Field Distribution in Multilayer Thin-film Polarizers

Abstract

The distribution of electric-field amplitude inside multilayer thin-film polarizers is evaluated for various polarizer designs. The polarizers, based on (H/2, L, H/2) as the basic stack, show higher field amplitude than those based on all quarter-wave layers. Here H and L represent quarter-wave layers of high- and low-index materials respectively. It has been pointed out that, to avoid damage to the polarizers in high-power laser systems, it is necessary to know the field distribution inside the layers both for radiation incident from the air-multilayer interface as well as the glass-multilayer interface. Some implications of the positioning of thin-film polarizers in Faraday isolators used in high-power laser chains are discussed in relation to the susceptibility of these polarizers to optical damage. The results indicate that the liquid-prism MacNeille polarizer shows a higher damage threshold, which can possibly be further improved by increasing the angle of incidence at the multilayer.     

Electrical properties of polycrystalline PTCR barium titanate

Semiconducting n-type barium titanate with a positive temperature coefficient of resistance (PTCR) has been made by doping BaTiO₃ with 0.4 mol% Ho₂O₃. The d.c. resistivity, a.c. resistivity (1.2 kHz) and relative permittivity (1.2 kHz) at different temperatures between room temperature and 523 K have been measured. The high relative permittivity and the PTCR effect are attributed to the existence of potential barriers at the grain boundaries as proposed by Heywang. The height of the potential barrier has been calculated as a function of temperature on the basis of the Heywang model, using the measured resistivity versus temperature and relative permittivity versus temperature above the Curie temperature. Several different kinds of electrode have been used to study the effect of the contact on measurements of resistivity and relative permittivity.     

Computer-Aided Permittivity Measurements of Moistened and Pyrolized Materials in Strong RF Fields (Part I)

This paper presents the results of computer-aided permittivity measurements (CAPM) on moistened paper samples, exposed to strong RF fields inside a microwave cavity. Permittivity measurements, sample weight, and RF power absorbed by the sample are monitored in real time by a microcomputer. From the CAPM, the permittivity values and the moisture content of the material are calculated. The effects of paper pyrolization on the permittivity measurements are examined, and a reversal in the measured dielectric parameters is observed at the 0-percent moisture level. This CAPM method is useful to examine the dielectric properties of materials critically dependent on the moisture content, for example, in food products and in the telephone wire industry where the insulating material is obtained from dried paper pulp. In addition, this CAPM technique can be applied to study the effects of thermal and RF shocks in dielectric materials such as used in high-power microwave windows or in studying the biological effects of microwave radiation using both short and long exposure cycles.     

Exact analysis of dispersive SAW devices on ZnO/diamond/si-layered structures

In this paper, a formulation for calculating the effective permittivity of a piezoelectric layered SAW structure is given, and the exact frequency response of ZnO/diamond/Si-layered SAW is calculated. The effective permittivity and phase velocity dispersion of a ZnO/diamond/Si-layered half space are calculated and discussed. The frequency response of an unapodized SAW transducer is calculated, and the center frequency shift caused by the velocity dispersion is explained. In addition, the electromechanical coupling coefficients of the ZnO/diamond/Si-layered half space based on two different formulas are calculated and discussed. Finally, based on the results of the study, we propose an exact analysis for modeling the layered SAW device. The advantage of using the effective permittivity method is that, not only the null frequency bandwidth, but also the center frequency shift and insertion loss can be evaluated     

Dielectric and structural characteristics of Ta2O5 anodic films formed in phosphoric acid electrolytes

The duplex nature of Ta₂O₅ films formed in H₃PO₄ electrolytes with different concentrations has been chanyotarired by net weight gain measurements of the films during the anodic oxidation, as well by capacitance and etch-rate measurements of the oxide films. The density and permittivity of each layer of the films formed in different concentrations of the electrolyte have been calculated.     

Microwave Properties of Yarns and Textiles Using a Resonant Microwave Cavity

Modified cavity perturbation methods for permittivity measurements of yarn and textile are described. A cylindrical cavity which is split into equal parts is designed to operate in the TE011 mode. The dielectric yarn is placed across the midplane of the cavity and a textile sample is placed in the cavity on a low-loss dielectric sheet in annular form. The shift in the resonant frequency and change in Q-factor are measured and the complex permittivity is calculated.     

Complex permittivity measurements of ferroelectrics employing composite dielectric resonator technique

Composite cylindrical TE(0n1) mode dielectric resonator has been used for the complex permittivity measurements of ferroelectrics at frequency about 8.8 GHz. Rigorous equations have been derived that allowed us to find a relationship between measured resonance frequency and Q-factor and the complex permittivity. It has been shown that the choice of appropriate diameter of a sample together with rigorous complex angular frequency analysis allows precise measurements of various ferroelectric. Proposed technique can be used for materials having both real and imaginary part of permittivity as large as a few thousand. Variable temperature measurements were performed on a PbMg(1/3)Nb(2/3)O3 (PMN) ceramic sample, and the measured complex permittivity have shown good agreement with the results of measurements obtained on the same sample at lower frequencies (0.1-1.8 GHz).     

High-extinction-ratio resonant cavity polarizer for quantum-optics measurements

The use of a high-finesse Fabry-Perot ring cavity with an odd number of reflections as a high-extinction-ratio resonant polarizer is shown. Experimental results from quantum-noise measurements using resonant cavities as spatial and spectral filters and precision polarizers are presented.     

A method for measuring the permittivity without ambiguity usingsix-port reflectometer

Automatic network analyzers are used for the broadband measurement of permittivity in different experimental arrangements. In many of them ambiguity appears because permittivity is calculated by solving a transcendental equation. This makes automatic measurements difficult. A method of eliminating this ambiguity is shown, with no additional experimental data required, except for a manipulation of the existing data. Theory and experimental results for low-loss dielectrics are shown for the short-circuited waveguide method using a six-port reflectometer. Errors are analyzed and several samples with permittivities of up to 16 are measured with an accuracy on the order of 1%     

A methodology for determining complex permittivity of construction materials based on transmission-only coherent,wide-bandwidth free-space measurements

An integrated methodology for determining the unique combination of complex permittivity based on measured transmission coefficient and time difference of arrival (TDOA) information in free-space measurements is proposed. The methodology consists of an estimation procedure of the real part of complex permittivity based on TDOA, and a root-searching procedure based on parametric system identification (SI) together with an error sum of squares (SSE) criterion. Generally, non-unique combinations of dielectric constant and loss factor are encountered when lossy or low-loss materials are measured and the proposed methodology is aimed at the determination of unique combinations of dielectric constant and loss factor for such materials. The proposed methodology is validated by measurements of several materials with known dielectric properties. The estimated complex permittivity values for Teflon, Lexan, Bakelite, and concrete are in good agreement with those reported in the literature. The method has potential for in-situ measurement of dielectric properties for construction materials. Applicability and limitations of the methodology are discussed.     

Computer study of methane adsorption by water clusters

Methane adsorption by water clusters including 50 molecules was studied by the molecular dynamics (MD) technique. The calculated frequency dependence of the real and imaginary parts of the dielectric permittivity points to the prevalence of a high-frequency mode in the spectra of these parameters after methane is adsorbed by water clusters. Such changes are also observed in the spectrum of the IR radiation absorption coefficient; however, the average value of this coefficient remains nearly the same. Methane adsorption causes a considerable increase in the reflection coefficient of the disperse water medium and the integrated power of IR radiation emission.     

A Combined Total Reflection-Transmission Method in Application to Dielectric Spectroscopy

A combined total reflection-transmission method for permittivity measurements at radio and microwave frequencies is described. Analytical expressions for the dielectric constant and the loss factor of a sample, viewed as a two-port in the transmission system, in terms of the measured scattering parameters are given. ne uncertainty of measurements of the dielectric constant and the loss factor is discussed and a method ofselecting an optimum sample length is suggested.     

Extraordinarily large permittivity modulation in zinc oxide for dynamic nanophotonics

The dielectric permittivity of a material encapsulates the essential physics of light-matter interaction into the material’s local response to optical excitation. Photo-induced modulation of the permittivity can enable an unprecedented level of control over the phase, amplitude, and polarization of light. Therefore, the detailed dynamic characterization of technology-relevant materials with substantially tunable optical properties and fast response times is a crucial step to realize tunable optical devices. This work reports on the extraordinarily large permittivity changes in zinc oxide thin films (up to −3.6 relative change in the real part of the dielectric permittivity at 1600 nm wavelength) induced by optically generated free carriers. We demonstrate broadband reflectance modulation up to 70% in metal-backed oxide mirrors at the telecommunication wavelengths, with picosecond-scale relaxation times. The epsilon near zero points of the films can be dynamically shifted from 8.5 µm to 1.6 µm by controlling the pump fluence. The modulation can be selectively enhanced at specific wavelengths employing metal-backed zinc oxide disks while maintaining picosecond-scale switching times. This work provides insights into the free-carrier assisted permittivity modulation in zinc oxide and could enable the realization of novel dynamic devices for beam-steering, polarizers, and spatial light modulators.     

Passive Integrated Optical Anisotropy-based Devices

Abstract

A new class of passive integrated optical devices based on dielectric anisotropy (birefringence) is described. In general, the allowed modes in uniaxial materials such as lithium niobate are hybrid. These modes have been calculated rigorously (i.e. without approximations) electromagnetically. Cut-off can occur, starting from either an unconditionally stable mode or a critically stable mode, through a transition to either a leaky guided mode or a leaky unguided wave. Passive cut-off anisotropy-based devices can be constructed simply by changing the direction of the channel waveguide on the anisotropic substrate. Example devices described include: high-pass filters, TE-pass polarizers, TM-pass polarizers, and temperature sensors (performing an absolute rather than a differential measurement). A design procedure for anisotropy-based devices is presented.     

Millimeter-wave dielectric properties of single-crystal ferroelectric and dielectric materials

Transmittance measurements on various single crystal ferroelectric and dielectric materials, BaTiO(3), SrTiO(3), LiNbO(3), LiTaO(3), (PbMg(1/3)Nb(2/3)O(3))0.73-(PbTiO(3))0.27, LaAlO(3), and Bi(4)Ge(3)O(12), over a broad millimeter-wave (MMW) frequency range have been performed. Frequency dependence of the complex dielectric permittivity has been measured in the MMW region using high-power sources for the first time, using a free-space, quasi-optical MMW spectrometer equipped with high-power backward wave oscillators (BWOs) as sources of coherent radiation, tunable in the range from 30 to 120 and 180 to 260 GHz. These results are compared with MMW permittivity of these materials obtained by other methods as well as to RF, microwave, and optical frequency permittivities for all the materials tested. The effects of both crystallographic orientation and quality of the surface polishing of the crystals have been examined. Uncertainties and possible sources of instrumentation and measurement errors related to the freespace MMW technique are discussed. This work demonstrates that precise MMW permittivity data can be obtained even on relatively small and thin crystals of different surface conditions and orientations using the high-power BWO-based quasioptical approach.     

Effects of annealing treatment on the dielectric properties of manganese-modified Pb(Fe2/3W1/3)O3 ceramics

The dielectric properties of thermally treated manganese doped Pb(Fe2/3W1/3)O3 (PFW) ceramics were investigated. Modifications of the dielectric properties by thermal annealing were observed. Air annealing causes a sharpening of the dielectric permittivity and an increase of the permittivity maximum values, more pronounced as the amount of manganese dopant increases. Oxygen annealing does not cause evident variations in the dielectric permittivity curve. The presence of oxygen vacancies is evinced by thermal gravimetric measurements. The role of oxygen vacancies, as well as the associations of manganese ions with oxygen vacancies, on the annealing process, is proposed and discussed. © 1998 Chapman & Hall     

Aligned Ag nanowires for radiation manipulation: efficient and broadband infrared polarizing beam splitter

We developed a numerical method to model and design infrared (IR) devices based on aligned metal nanowires on a flat substrate. Homogenization techniques and the transfer matrix method for birefringent-layered materials have been combined to obtain a simple but effective tool for tailoring and optimizing the optical properties of the resulting, strongly anisotropic system. As an example, we show the design of an efficient, broadband, IR polarizing beam splitter. With the emerging of new self-assembling techniques allowing orientation of metallic nanowires in uncomplicated and less-expensive ways, our results show a route to get a class of efficient, low cost and broadband IR polarizers.     

Optical Processing Using a Birefringence-based Spatial Filter

Abstract

It is well known that a suitably shaped birefringent material, placed between two polarizers, exhibits a spatial variation in amplitude transmittance. The present article explores the possibility of using such an arrangement as a spatial frequency filter. The advantage of such filters is that the nature of filtering achievable can be changed by rotating any of the two polarizers. The specific case of a biconvex quartz lens as a spatial frequency filter is considered and techniques for real-time edge enhancement and periodic noise removal are discussed. Experimental results are also presented.     

Broad-band dielectric spectroscopy of low-permittivity fluids usingone measurement cell

Dielectric spectroscopy is a relevant method for quality characterization of petrochemical products, provided that the permittivity spectra are measured with high precision over a broad frequency range. This paper describes how the permittivity of low-loss liquids such as crude oils can be measured with high precision using a single measurement cell in the broad frequency range 1 kHz to 6 GHz. The use of a single cell ensures that the whole dielectric spectrum is measured under the same conditions, which is an advantage for both on-line and laboratory applications. The permittivity spectrum is obtained by combining impedance and S-parameter measurements of a coaxial transmission/reflection cell with suitable permittivity calculation methods. The high sensitivity of the system is confirmed by measurements on crude oils and known low-loss liquids     

超材料宽带圆偏振器的研究进展

超材料因其独特的性质可以作为选择圆偏振光的器件,即圆偏振器。随着偏振分辨成像系统的重要性日益增强,圆偏振器已被用于增强对比度、圆偏振显微镜以及生物分子的检测,如氨基酸、DNA和具有固有手性结构的葡萄糖,尤其是在可见光波长下工作的圆偏振器已经引起了人们广泛的关注,已被用作控制复杂显示系统中光的偏振态的关键光学元件。然而通过传统方法获取圆偏振器有很大的局限性,如体积庞大、工作带宽窄等,极大地限制了它们的发展。近几年来,超材料中螺旋结构和堆叠结构的提出,促进了宽带圆偏振器的发展。本文简述了超材料中螺旋结构和堆叠结构形成宽带圆偏振器的偏振原理,详述了两种结构作为宽带圆偏振器的数值模拟和实验研究进展。