Method for designing an arbitrary continuous refracting surface with specified property of wavefronts conversion

A method is proposed for designing an arbitrary continuous refracting surface that can realize conversion between two specified distributions of wavefront. Optimization technique is avoided by solving a partial differential equation governing the surface-profile function. This equation is obtained using the property of congruence and the law of refraction, and its solution in this special case is found to be the same as that obtained in wavefront conjugation. A method based on finding the local coefficients of the surface is developed to solve the equation numerically, and an example is given to illustrate its feasibility.     

Angular interferometer using calcite prism and rotating analyzer

An interferometer using a calcite prism and rotating analyzer is proposed for angular displacement determinations. The calcite prism senses the angular displacements and the rotating analyzer transfers the interference signals from dc-type into ac-type. Compact optical setup and using low-cost devices are thus the advantages of the interferometer. The theory of the interferometer is first demonstrated. A setup constructed to realize the interferometer and the results of using this setup are then presented.     

Method for designing arbitrary two-dimensional continuous phase elements

We propose a method for designing arbitrary two-dimensional continuous phase elements. The phase anomalies that are due to amplitude zeros that occur in conventional design methods can be avoided completely with this method. Therefore the method is also useful for designing holographic elements that are free from amplitude zeros. The method is based on an iterative Fourier-transform algorithm. In the iteration process the method operates on the unwrapped phase. Consequently, a subsequent continuation step is not needed.     

Modelling optical fibres with arbitrary refractive-index profiles

The characteristics of various models of refractive-index profile are examined. Four models are considered: (1) power-law profile, (2) truncated even polynomial profile, (3) truncated all-term polynomial profile, (4) Gauss-Chebychev approximation. The characteristics of the various models are examined with particular reference to the ray-delay times and the shape of the impulse response. The results show that models (1) and (2) are limited in their usefulness in representing practical profiles, while the approximation (4) is easily applied to a variety of practical profiles.     

Angular emission profiles of dye molecules excited by surface plasmon waves at a metal surface

The angular distribution of fluorescence emission from dye molecules excited by surface plasmon waves in a silver film is reported. Coupling of the emitted fluorescence to a surface plasmon mode at the Stokes shifted wavelength results in a sharply peaked angular profile in the prism half space. Fresnel theory is used to model experimental results obtained for thick and thin sample dye films and for micron-size particles containing dye.     

Angular tolerance of Shack-Hartmann wavefront sensors with microaxicons

Wavefront sensing under nonparaxial conditions was studied with Shack-Hartmann setups based on arrays of microaxicons. The robustness of the generated pseudonondiffracting subbeams against tilt and axial displacement was demonstrated for ultraflat Gaussian- and inverse-Gaussian-shaped elements in transmission and reflection. To characterize slight aberrations and to identify optimum parameter fields, spatial moments of intensity profiles were analyzed with high sensitivity. Reflective design enables for wavefront sensing at oblique incidence as necessary for low-feedback detection and phase diagnostics of ultrashort pulses.     

Exact hole-bound states for semiconductor quantum wells with arbitrary potential profiles

An efficient numerical-analytical method for finding confined and continuum states in quantum-well systems with arbitrary potential profiles, described by coupled Schrödinger equations, is presented. The method is based on the analytical properties of the wave functions, in particular, the power series representation of solutions of the corresponding coupled differential equations. Using only the general properties of the coefficients of a system of an arbitrary number of coupled Schrödinger equations, and imposing for definiteness the simplest boundary conditions, we derive exact expressions for the wave functions and present methods for accurate calculations of the energies and wave functions of confined states and of the wave functions of continuum states in quantum wells. The method is applied to the calculation of the dispersion of hole bound states in a single GaAs quantum well with truncated parabolic confining potentials of different strengths. The results are compared with data available from previous calculations.     

Numerical method of designing three-dimensional open cloaks with arbitrary boundary shapes

In this paper, three-dimensional (3-D) open cloaks were designed based on the coordinate transformation method. When the transformation center point is close to the boundary of the cloaks, the material parameter tensors in the near-boundary areas of the cloaks approximate to those in the background, so the near-boundary areas can be designed to be open. Full wave simulations based on finite element method verified the open cloaks we designed. Open cloaks can exchange information and materials with background media. Using the design method proposed in this paper, the boundary of open cloaks can be arbitrarily shaped, which greatly enhances the applicability of open cloaks.     

Optimization of sensitivity encoding with arbitrary k-space trajectories

Sensitivity encoding (SENSE) is a magnetic resonance technique that unifies gradient and receive coil encoding. SENSE reconstructs the image by solving a large, ill-conditioned inverse problem, which generally requires regularization and preconditioning. The present study suggests a simple heuristic for determining the regularization parameter. Also discussed are the use of density weighting and intensity correction as preconditioners and the role that coil sensitivity estimation has in regularization. A modification to the intensity correction is proposed for use with a phase constraint.     

Interferometric tolerance determination for a Dove prism using exact ray trace

We use exact ray trace to calculate the interferometric Dove prism tolerance to manufacturing errors. We model the manufacturing errors by modifying the position of the prism vertices. The normal to the prism faces establishes the direction of the rays. We determine the prism tolerance by analyzing the optical traversed path rays. We evaluate the change in the image quality introduced by the normal deviation. When the manufacturing tolerance is maintained within ±0.35 arc sec, the maximum wave-front deviation is better than λ/10 at 633 nm. We found that a Dove prism with such tolerance introduces an OPD of two orders of magnitude lesser than a commercial Dove prism. The exact ray trace accuracy of the developed program is validated with the commercially available optical-design program OSLO™. The calculated tolerance complements a previous analysis of a Dove prism for its implementation in a rotationally shearing interferometer.     

Frequency selective surface with better polarization-independency for arbitrary incident angle

This paper investigates the frequency-selective property of a planar layer consisting of period arrays both theoretically and experimentally for different polarizations at arbitrary incident angle. The novel element is designed by loading the rectangular microstrip element with L-shaped conducting patch at its two ends. Based on the spectral-domain method, the frequency response including angle effect and polarization effect of the frequency selective surface (FSS) structure are analysed and the plots of the frequency versus transmission coefficient are obtained. As a result of the numerical analysis, it is shown that if the source polarization is changed, polarization-independence of previous FSS design can be achieved only for normal incidence, which limits most FSS applications. But in our proposed structure, the better polarization-independency for arbitrary incident angle can be achieved. It is observed that the simulated result comes very close to the experimental result.     

Hybrid photonics structures with grating and prism couplers based on ZnO waveguides

This paper presents the results of investigations concerning input-output systems of an electromagnetic wave in the visible and near visible spectrum for their application in structures of integrated optics. The input-output structures used in described planar optical waveguides are in a form of prism and grating couplers. The first part of the paper contains numerical analysis of grating couplers aiming at an optimization of their geometrical parameters, strictly — the depth of the grooves in the grating coupler. The second part presents the practical realization, as well as experimental tests of the planar optical waveguide with the hybrid input-output system. As the input system of the electromagnetic wave, a prism coupler was used, and in the case of the output system — a photonic structure with grating coupler was applied. The investigated planar wave guides with the input-output structures were made of a wide energy band gap semiconductor — zinc oxide (ZnO).     

Analytic methods for field induced tunneling in quantum wells with arbitrary potential profiles

Electric field induced tunneling is studied in three different types of quantum wells by solving time-independent effective mass equation in analytic methods based on three different Airy function approaches. Comparison of different Airy function methods indicates that they are identical and connected to each other by the Breit-Wigner formula.     

Modal analysis of circular Bragg fibers with arbitrary index profiles

A finite-difference approach based upon the immersed interface method is used to analyze the mode structure of Bragg fibers with arbitrary index profiles. The method allows general propagation constants and eigenmodes to be calculated to a high degree of accuracy, while computation times are kept to a minimum by exploiting sparse matrix algebra. The method is well suited to handle complicated structures comprised of a large number of thin layers with high-index contrast and simultaneously determines multiple eigenmodes without modification.     

纳弧度分辨力角位移传感器及平均灵敏度标定

给出了基于六次临界反射棱镜的精密角位移传感器,采用的是差动式结构。实验结果表明,传感器灵敏度高,量程为500μrad,具有5nrad的分辨力。提出了适合于小量程角位移传感器的平均灵敏度的标定方法,可以快速标定平均灵敏度,降低标定过程中标定系统及传感器自身漂移对标定精度的影响。     

The block Schur algorithm for designing optical multi-layered structures

We present how to use the block Schur algorithm to design optical multi-layered filters. The block Schur algorithm can, in turn, be applied to find reflection coefficients of optical multi-layered filters. We show that the block Schur algorithm using the block matrices is faster than the standard Schur algorithm using the scalar elements on vector processor. The optimum sub-matrix size for the block Schur algorithm on CRAY Y-MP C98 supercomputer is also suggested.     

Modeling of waveguide UV-induced Bragg gratings with arbitrary apodization function: Tools for designing high-performance related devices

We present a semi-analytical modeling suitable for the investigation of the spectral characteristics of UV-waveguide Bragg gratings (UV-WBGs) having arbitrary apodization function and extending both in the film layer and in the overlayer. The modeling is based on a proper combination of coupled mode theory and transfer matrix formalism and provides a powerful tool for designing and simulation of complex UV-grating based structures. The results of a detailed investigation of UV-WBGs in doped silica based channel optical waveguides are presented and critical issues for upgrading the performances of related device are discussed. Validation of the modeling is provided by means of an extensive comparison between theoretical and experimental results relevant to UV-WBGs realized in phosphorous (P)- and boron (B)-doped silica based waveguides.     

Enhancing sensitivity of a contactless method for measuring profiles and revealing macrodefects in composite periodic structures of the transmission type

Various interference techniques for comparing individual periodic structures incorporated into a transmission-type composite are suggested. All of the techniques are based on the method of interference patterns resulting from superposition of waves diffracted by the elementary periodic structures. It is shown that the sensitivity of measurements can be significantly enhanced and the width and direction of reference fringes can be arbitrarily adjusted. An interference-moire technique allowing a comparative study of elementary periodic structures incorporated into the composite is considered. Efficiency of the technique is confirmed experimentally.     

Analysis of periodic thin-film structures with rectangular profiles

A rigorous analysis is presented for thin-film structures on which a rectangular-profile grating layer is superimposed. Typical dispersion curves are calculated for guided leaky waves, which are relevant to beam couplers in integrated-optics applications.