Analysis of polarization rotation in periodically loaded ribwaveguides by transfer matrix method

A novel transfer matrix method is employed for the analysis of polarization rotation in an asymmetrically periodically loaded rib waveguide. The transfer matrix method is based on the hybrid local normal modes. The vector normal modes are approximated by a linear combination of the scalar modes. In comparison with the coupled-mode analysis, this approach takes the radiation loss due to scattering at the junctions of the periodic loading into account. A new simple analytical solution in the power coupling for the periodically loaded rib waveguide is derived. Analytic results are shown for some typical structure and compared with results by more rigorous numerical methods     

Simulation of three-dimensional optical waveguides by a full-vectorbeam propagation method

Simulations of optical guided waves in three-dimensional waveguide structures by a full vector beam propagation method are described. Two sets of coupled equations governing the propagation of the transverse electric and magnetic fields are derived systematically. Polarization dependence and coupling due to the vectorial nature of the electromagnetic fields are considered in the formulations. The governing equations are solved subsequently by finite-difference schemes. The vector BPM is first assessed for a step-index circular fiber by comparing the numerical results with the exact analytical solutions. The guided modes of a rib waveguide are then investigated in detail. Comparisons among the scalar, semi-vector and full-vector simulations of the rib waveguide are made. Finally polarization rotation of a periodically loaded rib waveguide operated fully based on the vector nature of the electromagnetic waves is modeled and simulated     

Vectorial simulation of passive TE/TM mode converter devices on InP

Accurate calculations of polarization rotation at abrupt waveguide interfaces are performed by a vectorial two-dimensional finite difference scheme. It is shown that the small orthogonal component of the vector field in rib waveguides can play an important role in mode polarization rotation. Polarization rotations in mode converters fabricated on InGaAsP/InP by periodically arranged tilted waveguides or periodic loading of the rib are explained by these calculations, and design rules for passive mode converter devices are given     

TE/TM mode splitters on InGaAsP/InP

In a monolithic heterodyne polarization diversity receiver, mode splitters which effectively separate the TE and TM polarization of the optical wave are required. For this purpose, a directional coupler which utilizes a metal cladding on one of its branches to separate both polarizations was investigated. The polarization splitters can act in two distinct modes of operation, depending on the degree of lateral confinement of the optical rib waveguide before an asymmetric coupler. For weak confinement, the metallized waveguide is guiding for TE- but nonguiding for TM-polarization, and negligible TM-crosstalk results     

Analysis and measurement of polarization conversion in a periodically loaded dielectric waveguide

The full-vectorial beam-propagation method with the improved finite-difference formula is applied to the analysis of a TE/TM mode converter based on an asymmetric periodic loaded waveguide. The polarization conversion behavior is measured at a microwave frequency. It is demonstrated that the calculated complete conversion length is in agreement with the experimental result.     

Some Results for Thin-Iris Loaded Periodic Waveguides

The planar waveguide holding planar obstacles is a prototype structure--its fields correspond to some sets of lowest modes in circular and coaxial line waveguides that use coaxial iris loading and in inductive iris loaded rectangular guides. An analysis of a periodically thin-iris loaded planar waveguide is offered, the procedure for which can also be applied to the other waveguides mentioned. A particular example for small iris separation is considered. Among the results of this study are adjustments to some formulas of Brillouin so as to allow consideration of large phase shifts per cell of periodic guide. The procedure, which can be recommended as a formula deriving technique, can find use with such other planar obstacles as the thick periodic iris, the interdigitally placed irises, or the single iris in a multimode guide. Some consideration is given to interdigital loading.     

Theory of polarization rotation and conversion in verticallycoupled microresonators

Two orthogonally polarized waveguide modes can exchange power through an intermediate level, if the polarization state of that level is tilted with respect to the polarization states of the waveguide. Microrings with modest sidewall angles support such tilted modes. Ultracompact, wavelength selective polarization rotators might be achieved. Simple analytic expressions are derived for polarization rotation by vertically-coupled resonators in terms of geometrical factors     

Performance of an array of circular waveguides with strip-loadeddielectric hard walls

An infinite planar periodic antenna array of radiating open-ended circular waveguides is considered. The conducting waveguide walls are covered with dielectric layers loaded with longitudinal conducting strips for providing the hard wall boundary condition. Analysis of the array is carried out by the mode-matching method. The waveguide modes involved in the method are calculated by using the asymptotic strip boundary condition. It is shown that they are split into an independent subsystem of TE modes for the whole cross section and two independent subsystems of TM modes: one is for the central region and another is for the layer region. The calculations show that the operation of the hard waveguides in an array with small element spacing is similar to that of the multimode smooth wall waveguides completely filled with dielectric. For large diameters and element spacing, the hard waveguides have significant advantages over the smooth ones. It is shown that unlike an individual hard waveguide, the aperture efficiency of such a waveguide in the array has a nonmonotonic dependence on the waveguide radius. The results characterizing the behavior of the aperture efficiency and cross-polarization level in a frequency band as well as the contribution of certain waveguide modes in the reflected power are presented and discussed. The examples of the element patterns corresponding to minimal cross polarization are also given     

Wide-Band Polarizer In Circular Waveguide Loaded with Dielectric Discs

A converter between linear and circular polarization has been designed in circular waveguide by the use of periodic loading with oblong dielectric discs. The disc loading increases the single-mode (TE-11) bandwidth relative to that of homogeneously filled circular waveguide. Moreover, periodic loading gives the designer freedom to adjust the disc thickness and shape to meet certain requirements. With the abutting disc-loaded waveguide as a reference, the dielectric loading is increased in one plane of polarization and decreased in the orthogonal plane. In a wide-band design, this differential loading gives nearly constant 90/spl deg/ difference in time phase between space-quadrature component waves, the condition for circular polarization. Such a polarizer has been constructed with four oblong discs. Across a frequency bandwidth of about 15 percent, the measured phase difference is within 2/spl deg/ of the desired value and the SWR is within 1.5 dB.     

Investigation into Polarization of Unloaded and Loaded Microstrip Square-Ring Antennas

The polarization characteristic of unloaded and loaded square-ring microstrip antennas is investigated. Several different loading types like single-stub, dual-stub, notch, gap and shorting-pin are considered and their effects are studied. Loading enables feeding using a 50-Omega probe. The simulation and measurement results show that the loading techniques excite a loaded TMy ₁₁ mode that is orthogonal to the unloaded TMx ₁₁ mode. This indicates that by loading the ring antenna its polarization can be switched adaptively. However, the purity of the loaded and unloaded modes depends on the loading type. For some loading types like gap and shorting-pin, the excitation of the unloaded mode seems negligible, in comparison to the loadings by stub and notch. For the stub and notch loaded antennas the unloaded mode is also present, and its excitation efficiency is frequency dependent. Thus, their polarization plane, which is due to both loaded TMy ₁₁ and unloaded TMx ₁₁ modes, also becomes frequency dependant. The results of this investigation can be useful in selecting the loading methods for high-impedance microstrip ring antennas, and control of their impedance and polarization. The knowledge of the antenna polarization is essential in communications, and its dependence on the loading type can be used as an important parameter in design of adaptive antennas and sensors.     

High-performance traveling-wave electroabsorption modulators utilizing mushroom-type waveguide and periodic transmission line loading

For the first time, periodic loaded electrodes and mushroom-type waveguide are combined to improve the performance of traveling-wave electroabsorption modulators (TWEAMs) based on the asymmetric intra-step-barrier coupled double strained quantum well (AICD-SQW). The electrical modulation response of periodic mushroom-type TWEAM is obtained by using equivalent circuit model, and is compared with simulation result of conventional mushroom-type TWEAM counterpart. The equivalent circuit model simulation results indicate that for the exemplary modulation length of 300 mm, the mushroom-type TWEAM with periodic transmission line loading can achieve much wider bandwidth about 99.7 GHz and 43.1 GHz than the conventional counterpart with about 43 GHz and 33 GHz for 35 W and 45 W terminations, respectively.     

Broad-Band Ferrite Rotators Using Quadruply-Ridged Circular Waveguide

It has been shown that the rotation of the plane of polarization of a wave propagating in a magnetized unbounded ferrite medium should be independent of frequency. However this is not the case when a ferrite rod of small diameter is placed within a waveguide. For example, if a ferrite rod one-quarter inch in diameter in a fifteen-sixteenth inch diameter circular waveguide is used, the rotation will change by a factor of four to one over the frequency band from 8000 to 10,000 mc. This variation in rotation is substantially due to the waveguide characteristics, and can be minimized by lowering the cutoff frequency of the waveguide. Various methods of lowering the cutoff of circular waveguide are compared. Data on the broadbanding of the rotation by dielectric loading and also by the use of quadruply-ridged circular waveguide is shown. An experimental study showing the effect of the ridge width and height on the cutoff of the circular waveguide and the frequency dependence of the rotation is discussed.     

Integrated optical waveguide polarizer based on photobleaching-induced birefringence in an electrooptic polymer

A TE-pass waveguide polarizer is fabricated by utilizing the photobleaching-induced birefringence at room temperature in an electrooptic polymer. The polarizer consists of the photobleached waveguide supporting only TE mode, which is integrated in the middle of the etched rib waveguide supporting both TE and TM modes. It has a simple structure and requires no high temperature process like poling. The measured polarization extinction ratio is about 21 dB at the wavelengths of 1.3 and 1.55 /spl mu/m, and the estimated excess loss is about 0.4 dB.     

A Lossy Dielectric-Ring Loaded Waveguide With Suppressed Periodicity for Gyro-TWTs Applications

A dielectric-loaded (DL) waveguide is an attractive possibility for interaction circuits with high-power sources in the millimeter-wave regime down to tenths of millimeters, particularly for gyrotron-traveling-wave-tube amplifiers (gyro-TWTs). We present results on a systematic investigation of the influence of the periodically loaded lossy dielectric on the propagation characteristics of the operating modes, which reveals that a complex mode in the periodic system can be mapped to a corresponding mode in an empty waveguide or a uniform DL waveguide. Dielectric losses not only induce modal transitions between different modes with similar field structures and close phase velocities in the uniform system but also unify the discrete mode spectrum into a continuous spectrum in the periodic system. Since the lossy dielectric functions as a power sink, the higher order Bloch harmonic components arising from the structural periodicity are suppressed, and the mode spectrum of the lossy periodic system degenerates into that of an empty waveguide. This alleviates the potential danger of spurious oscillations induced by the higher order harmonic components, making the periodic lossy DL waveguide promising in a high-power millimeter-wave gyro-TWT.     

Analysis of polarization independent optical amplifiers and filtersbased on polarization rotation in periodically asymmetricwaveguides

Polarization rotation in periodically asymmetric passive and active waveguides is described theoretically. The analysis is based on the vector wave equation and analysis of the coupled mode equations. It is shown that these periodically asymmetric active waveguides can be employed as polarization-independent optical amplifiers, and that strictly polarization-independent amplifiers require a rotation of an integer multiplier of π radians. An illustrative example of such an amplifier with a buried waveguide structure suitable for monolithic integration is analyzed. Polarization-insensitive passive Bragg filters employing, in addition to the ordinary grating, a periodically asymmetric perturbation are also considered, and polarization rotation in a distributed feedback laser filter is discussed     

周期损耗介质加载波导与均匀圆波导间的模式映射

损耗介质环与金属环间隔加载的周期损耗介质波导能够有效地控制各种模式的衰减特性,这对于抑制毫米波回旋行波管放大器的绝对不稳定性和提高其性能具有重要作用.针对应用于Ka波段、TE01模的回旋行波管放大器的周期损耗介质加载圆波导,系统地分析了该周期系统与均匀系统间的模式映射关系.研究表明,当介质层厚度一定时,均匀介质加载波导中的高阶模式可以映射为光滑波导中的低阶模式,且相互映射的模式在中空区域的场型一致.周期系统中的模式表现出复合模式的分布.在一个周期中,介质段和金属段的模式分别映射为均匀介质波导和金属波导中的模式.明确周期介质加载波导系统与均匀波导系统间的模式映射关系是分析发生在这种复杂的互作用回路中的回旋电子脉塞注波互作用的前提,对简化其物理模型具有指导作用.     

波纹波导极化器的分析

极化器是天线馈电系统中的重要器件,但传统的极化器带宽一般很窄。介绍了一种新型的宽带极化器(波纹波导极化器),其结构是在方波导的两壁加载横槽波纹,使波导中的2个正交模产生了90°的相位差。因而将线极化信号转化成圆极化信号。波纹波导极化器在超过30%的带宽内仍然有很好的相移特性,因此他在宽带反射面天线馈电系统中有着很广阔的应用。     

A simple variational approach to optical rib waveguides

A simple method for the calculation of the mode properties of optical rib waveguides is presented. The method is based on a scalar variational principle combined with a vector perturbation analysis for the polarization correction. It is demonstrated that, with the proper trial functions, the approach can predict very accurately the dispersion characteristics with much less effort (in terms of formulation and computation) than the existing numerical techniques. The field patterns of the modes can be computed from the scalar analysis. The vector property of the mode can be taken into account by a perturbation formula. The computation is carried out on an IBM PC. The user-friendly computer program is written in Fortran     

Vector beam propagation analysis of polarization conversion in periodically loaded waveguides

An improved design of a short and low-loss polarization converter is proposed. It consists of an asymmetrically periodic loaded rib waveguides. At a wavelength of 1.5 /spl mu/m, 98% polarization conversion ratio is obtained with a relatively short 0.74-mm device length and an extremely low 0.13-dB total insertion loss. The simulation results are obtained using a full vector beam propagation method based on the finite element method.     

Polarization properties of a fiber-to-asymmetric planar waveguidecoupler

A coupled mode model describing the light transfer between a single-mode fiber and a planar asymmetric waveguide, which takes into account the two dimensions of the waveguide cross sections, as well as the TE or TM polarization of the planar waveguide modes, is presented. This model is applied to the practical case of a distributed (curved fiber) coupler, and the possibility of light modulation by changing the refractive index: of the cover medium is pointed out. The action of such a coupler as a polarizer, which could be externally driven, is also considered