Polarization-dependent nonlinear gain in semiconductor lasers

We have numerically studied the nonlinear gain coefficients in terms of spectral hole burning for the optical fields in parallel and orthogonal polarizations in semiconductor lasers by solving the equation of motion for the density matrix in perturbation series. The electronic band structures and the transition matrix elements used in the calculations are obtained by diagonalizing Luttinger's Hamiltonian. In the present analysis for InGaAsP lasers, the cross-saturation coefficient for the parallel polarizations is twice as large as the self-saturation. Also, the cross-saturation coefficient for the orthogonal polarizations, which affects the polarization switching and polarization bistable operations of the laser, rests between the two. The relative magnitude of self-saturation coefficients and cross-saturation coefficients for orthogonal polarizations satisfies the condition for polarization bistable operations. We also discuss the effect of carrier heating on gain saturation coefficients     

Electromagnetic scattering from anisotropic plasma-coated perfect electromagnetic conductor cylinders

The scattering of electromagnetic waves by a perfect electromagnetic conductor (PEMC) cylinder coated with a homogeneous plasma anisotropic material is studied in this paper. Both of the transverse electric and the transverse magnetic polarizations of the incident waves have been analyzed and formulated. The presented analysis and formulations are general for any perfect conductor cylinder (PEC, PMC, or PEMC) with general isotropic/anisotropic material coatings that include plasma and metamaterials. The co-polarized and the cross-polarized components of the scattered fields are computed for different cases of the anisotropic plasma coated PEMC cylinders and for an anisotropic plasma column. Bistatic echo widths for the cases of PEMC, PEC (perfect electric conductor) and PMC (perfect magnetic conductor) cores have been computed and compared. The behavior of the monostatic echo width with the variation of the admittance parameter for the co-polarized and the cross polarized fields is also investigated. The comparisons of the computed results of the presented formulations with the published results of some special cases confirm the accuracy of the presented analysis.     

Polarization state of the emission of external grating diode lasers

The laser emission of transverse electric (TE) and transverse magnetic (TM) polarization, in alternating successive spectral ranges, that can occur when external grating diode lasers are wavelength tuned, is theoretically and experimentally investigated. The modulated threshold gain curves of the external cavity for the two polarizations can be made to intersect with each other if a grating is used in such a way as to practically eliminate the difference between the laser diode losses and confinement factors for TE and TM polarization. The result is a sequence of wavelength ranges where the threshold gain is alternately lower for the TE resp. TM polarization. Within each range, a wavelength tunable single mode laser emission is obtained. The phenomenon is described, taking into account the characteristics of the key components of the external cavity, i.e., laser diode structure, antireflective (AR) coating, and grating efficiency. Design tools are proposed for the characteristics of the components necessary for the development of such an external cavity. The theoretical and design concepts are experimentally confirmed in a number of external cavities, using diode lasers emitting around 1.5 μm, with different types of antireflective coatings, as well as different grating configurations     

Efficient solution for backscattered field of a dihedral cornerreflector

The problem of transverse magnetic (TM) plane wave scattering from a dihedral corner reflector is investigated. Using the mode matching technique (MMT), the transmitted and scattered fields are expressed in the angular spectral domain in terms of radial waveguide modes. The boundary conditions are enforced to obtain simultaneous equations for the transmitted and scattered fields. The simultaneous equations are then solved to represent the fields in a series form. Numerical results obtained by this method compare favourably with those obtained by other methods     

Sampling method using prefiltered band-limited Green's functionsfor the solution of electromagnetic integral equations

In the context of far-field scattering, the spatial spectrum of fields or currents on a scatterer may be approximated as band-limited. On this premise one can greatly simplify the computation of radiation integrals by eliminating in advance those spectral components of the Green's function not expected to be present in the fields. This approach enables one to dispense with the notion of basis functions and, instead, represent fields and currents as well as the impedance matrix representing the Green's function entirely in terms of a sparse set of samples, thereby obviating the need for integration. Moreover, by taking full advantage of the band-limited character of the solution, this sampling theoretical approach yields an efficient representation with a minimal number of degrees of freedom. The method was explored for scattering from two-dimensional perfect electric conductors including ellipsoidal cylinders and flat strips, in both polarizations, using uniform as well as nonuniform sampling, and yielded surprisingly good results     

Analysis of the electromagnetic scattering by thick gratings usinga combined FEM/MM solution

The problem of diffraction by a thick, conducting grating situated in an inhomogeneous dielectric slab is investigated using the generalized network formulation. This formulation combines the method of moments and the finite-element method, permitting the treatment of periodic elements of arbitrary cross section and inhomogeneous profiles. Solutions are presented for both transverse electric (TE) and transverse magnetic (TM) polarizations. Transmission gratings composed of rectangular conductors filled with dielectric materials of arbitrary profiles are studied     

衍射微柱透镜轴向光强分布特性的严格电磁分析

衍射聚焦器件轴向光强分布的焦深和焦移特性，直接决定着系统接收面的装配误差和获得最佳的能量利用率。当器件的口径和面型特征尺寸可与照射波长比拟时，必须考虑光波与衍射器件的电磁作用。利用严格电磁分析方法——时域有限差分法，对有限口径衍射微柱透镜的轴向光强分布进行了严格分析，并且与传统的标量分析方法进行详细比较。分析比较了TE和TM极化波入射情况下，不同面型分布(8台阶，16台阶量化面型和连续面型)的衍射微柱透镜焦深和焦移特性与透镜F数的关系。结果表明透镜轴向光强最大点向透镜面偏移，焦移量的严格计算结果要大于标量计算结果，表明透镜的快聚焦特性，而二者得到的焦深量基本一致，同时两种理论方法都表明透镜焦深和焦移随F数的增加而增加。     

铁电薄膜的厚度对其相变性质的影响

当铁电薄膜的厚度改变时,利用平均场近似方法,研究了基于横场伊辛模型的铁电薄膜的相变性质。在文中利用数值计算方法计算了不同厚度的铁电薄膜的相图和居里温度。研究结果表明,厚度对铁电薄膜的相图会产生明显的影响,但对居里温度则几乎没有影响。     

Centimeter-wave microstrip phase shifter on a ferrite-dielectricsubstrate

The propagation characteristics and fields of a microstrip transmission line on a composite ferrite-dielectric substrate are studied with a focus on its phase-shifting behavior. Two different methods are used for theoretical analysis, namely, the least-squares boundary residual method, which offers high precision, and a variational method in the spectral domain which requires a low computing time. Quasi-TEM (transverse electromagnetic) propagation is assumed in both cases. The results obtained are compared to experimental data, and good agreement is observed. Besides its easy design, this phase shifter presents the advantage of having a good peak power handling capacity as well as a low production cost because of the ease with which it can be integrated in planar systems     

Electromagnetic wave propagation in multilayer dielectric periodicstructures

The propagation characteristics in multilayer dielectric periodic structures, that extends a previous analysis by introducing additional dielectric layers, is presented. It is applied to propagating electromagnetic modes along the longitudinal and transverse directions of the structure's periodicity. The use of Floquet's theorem reduces the analysis to a single cell of the propagating fields for both, TE and TM polarizations. Results showing the effect of varying the layers thickness and electric permittivity on the propagation constant and on the field distributions within each cell are presented as well as the band structure associated with the periodic structure     

Scattering from narrow rectangular filled grooves

The solution of the integral equation for a small width rectangular groove is considered. It is shown that by retaining the dominant mode supported by the rectangular groove, the resulting quasi-static integral equations are comparable to those associated with the perfectly conducting narrow strip. They are, therefore, amenable to analytic solution yielding the exact field distribution or equivalent currents across the groove's aperture. The derived currents exhibit the same edge behavior as that associated with the currents of a perfectly conducting half-plane. The corresponding current behavior based on a (numerical) impedance simulation of the groove is quite different. However the resulting echowidths are comparable. Both transverse electric (TE) and transverse magnetic (TM) polarizations are treated     

Spectral resolution and solution of field problems in an anisotropic and compressible medium

It is shown that when source currents are present in a compressible and anisotropic plasma, the longitudinal components of the electric and magnetic fields and the pressure variation satisfy a coupled inhomogeneous equation. Based on the spectral resolution of a square matrix, a general method for the solution of such an equation is presented. The solution of the coupled-wave equation is thus reduced to the evaluation of some simple integrals. Formulas for the determination of the transverse components are given. To demonstrate the simplicity of the method, fields due to a magnetic line source are worked out in detail. Some numerical results are also included.     

Numerical analysis and validation of the combined field surfaceintegral equations for electromagnetic scattering by arbitrary shapedtwo-dimensional anisotropic objects

The numerical solution of coupled integral equations for arbitrarily shaped two-dimensional, homogeneous anisotropic scatterers is presented. The combined theoretical and numerical approach utilized in the solution of the integral equations is based on the combined field formulation and is specialized to both transverse electric (TE) and transverse magnetic (TM) polarizations. As opposed to the currently available methods for anisotropic scatterers, the present approach involves integration over the surface of the scatterer in order to determine the unknown surface electric and magnetic current distributions. The solution is facilitated by developing a numerical approach employing the method of moments. The various difficulties involved in the numerical effort are pointed out, and ways of overcoming them are discussed in detail. The results obtained for two canonical anisotropic structures, namely, a circular cylinder and a square cylinder, are given and validated by results obtained by alternative methods     

Design and Analysis of an Ultra-Compact and Ultra-Wideband Polarization Beam Splitter Based on Coupled Plasmonic Waveguide Arrays

We present the design of an ultra-compact polarization beam splitter where three symmetrical dielectric channel waveguides are hybrid integrated with Au plasmonic waveguide arrays. Ultra-wideband operation over 50 THz with the insertion loss less than 2 dB for both transverse electric and transverse magnetic mode are predicted. The extinction ratio is better than 15 dB for both polarizations and it is realizable on a chip size as small as 0.93times4.2 mum².     

Full-wave modeling of coplanar waveguide discontinuities withfinite conductor thickness

An extended version of the spectral domain approach (SDA) is developed to analyze discontinuities in open coplanar waveguide with finite metallization thickness. By making use of the exact Green's function in the spectral domain, the effects of surface wave and radiation phenomena are accurately accounted for. Both longitudinal and transverse components of the aperture electric fields are used in the analysis to allow modelling of structures with large transverse dimensions at high frequencies. The procedure also includes mode conversion near the discontinuities. As an illustration of the method, analytical steps and computed scattering parameters of the coplanar waveguide short-circuits and transitions are provided and compared against measured data     

A semivectorial finite-difference time-domain method (optical guided structure simulation)

A semivectorial finite-difference time-domain method (FDTD) that solves the vector wave equations for the transverse electric fields is presented and validated. By taking into consideration the boundary conditions for the transverse, electric fields in the finite-difference scheme, the polarization effect of the electromagnetic waves can be modeled. In comparison with the full vector FDTD, the present approach requires less memory and is more computational efficient. The method is validated by a comparison with the exact analytical solutions as well as the full vector FDTD results and is shown to be very accurate.<>     

Axial slot antenna on dielectric-coated elliptic cylinder

The radiation properties of an axial slot antenna on a conducting elliptic cylinder with a homogeneous dielectric coating are investigated. In the dielectric coating and in the exterior free-space region the field is expanded in elliptic waves using the Mathieu functions. The Mathieu angular functions are employed as basis and testing functions to enforce the boundary conditions at the interface between the dielectric and the free-space regions. The equations of continuity at the boundary are solved by Galerkin's method. Numerical results are presented in graphical form for the transverse electric (TE) and transverse magnetic (TM) polarizations to illustrate the far-field radiation patterns, the gain versus coating thickness, and the aperture conductance versus coating thickness     

Spectral FDTD: a novel technique for the analysis of oblique incident plane wave on periodic structures

This paper introduces a new technique which calculates the reflection coefficient for the plane wave incident on planar periodic structures. The method referred to as spectral finite-difference time-domain (SFDTD) replaces the conventional single-angle incident wave, with a constant transverse wavenumber (CTW) wave. Because the transverse wavenumbers are constant, the fields have no delay in the transverse plane (x-y plane), and PBC (periodic boundary condition) can be directly implemented in the time domain for both oblique and normal incident waves. The stability criterion for this new FDTD technique is angle-independent and therefore this method works well for incident angles close to grazing (/spl theta/=90/spl deg/) as well as normal incident (/spl theta/=0/spl deg/). This shows the efficiency of the method compared to other available FDTD techniques for the same purpose that force a more restricted stability criterion as angles turns to grazing. The validity of this method is verified by comparing the reflection coefficient calculated by this method with the analytical results of a grounded slab. The results of this technique are also compared with method of moments for a periodic array of metallic patches and a good agreement is observed. A periodic array of metallic patches above a PEC plate is analyzed and the reflection coefficient is calculated over a wide frequency band for angles varying from 0/spl deg/ to close to 90/spl deg/.     

Fast and accurate algorithm for electromagnetic scattering from 1-D dielectric ocean surfaces

A fast and accurate multigrid (MG) algorithm is presented for the direct method-of-moments (MoM) numerical simulation of radar scattering from large-scale one-dimensional (1-D) dielectric randomly rough surfaces. The proposed MG algorithm combines the desirable features of the generalized conjugate residual preconditioned iterative procedure and a parallel implementation of the spectral acceleration scheme proposed by Chou and Johnson. In addition, the paper proposes effective preconditioning schemes designed to further enhance the numerical efficiency of the proposed algorithm. The accelerated MG algorithm was benchmarked against the exact MG solution for both transverse electric and transverse magnetic polarizations. The efficiency of the proposed algorithm facilitates scattering calculations from electrically large surfaces. Hence, the algorithm was used to assess the performance of an approximate physical-optics scattering model used for ocean forward scattering simulations at the Johns Hopkins University Applied Physics Laboratory (JHU/APL). The validations are performed at X-band and W-band frequencies.     

Gaussian beam scattering from a conducting cylinder partially buried in a ground plane

The problem of scattering from an infinitely long conducting cylinder that is partially buried in a perfectly conducting ground plane due to an obliquely incident gaussian beam is solved by an exact procedure based on the method of images by first adopting a simplification originally proposed by Kozaki. The incident and the specularly reflected fields are expressed in terms of cylindrical vector wave functions multiplied by a weighting function which involves the beam parameters like the radial distance of the source and beam width. The scattered fields originating from the cylinder and its image in the ground plane are expressed in terms of cylindrical vector wave functions. The boundary conditions on the surface of the cylinder are then imposed and this procedure leads to a coupled infinite system of equations for the even and odd mode expansion coefficients of the scattered field. These equations are solved numerically for the case of cylinders having electrical radius in the Rayleigh and resonance regions. Both the transverse magnetic and transverse electric polarizations of the incident beam wave are considered and some representative numerical results for the scattered far-field are presented in graphical form. The magnitude of the induced current for the TM polarization is calculated and compared with the corresponding case of plane wave incidence.