Radiation loss in dielectric waveguide structures by the volume current method

The volume current method (VCM) is used to evaluate the radiation loss of dielectric waveguide structures. This perturbation technique is applicable to practically any waveguide structure. The radiation loss of two- and three-waveguide coupled wave structures is calculated. The theory leads to design criteria for the minimization of the radiation loss of these structures. The problem of radiation loss in bent waveguide is solved with the new formulation. Some properties of radiation from a bend are described. The expression for the bend-loss reduces to that in the literature.     

A novel wide-angle low-loss dielectric slab waveguide Y-branch

A new Y-branch structure for dielectric waveguides is proposed and analysed using simple geometrical optics and beam propagation methods. It is shown both qualitatively and quantitatively that the proposed structure has larger branching angles but lower radiation loss than those associated with either conventional Y-branches or structures with antenna coupled and phase front accelerators. The optimal design parameters calculated by numerical simulations are in very good agreement with those found from the geometrical optics. The simulations also reveal that the performance is fairly insensitive to fabrication errors     

Radiation loss of Y-junctions in rib waveguide

In this paper we analyze the effects of radiation in Y-junctions in rib waveguide by combining the effective dielectric constant method and the concept of local modes of a five-layer slab guide. The evaluation of the fields of the junction is performed together with the analysis of the radiation effects at the end of the transition; various kinds of junctions are examined and discussed, in both LSE and LSM polarizations     

Radiation characteristics of a dielectric disk-loaded circularcylindrical waveguide

The radiation pattern of a circular cylindrical waveguide that is loaded inside with periodically spaced dielectric disks is derived by considering the region between two disks as a medium with anisotropic permittivity and using Schelkunoff's equivalence principle. The far-field electric field components and their relationship to cross-polarization ratio are determined. The variation of the latter quantity with the size, spacing, and dielectric constant of the dielectric disks is studied     

Dissipation loss of mid-infrared radiation in a dielectric waveguide

Dissipation loss of electromagnetic radiation with wavelengths of 20–55 μm was theoretically studied in a three-layer planar dielectric insulating waveguide combined with a heterolaser. It was shown that the dependence of the loss on the waveguide layer thickness behaves differently for different wavelengths in the range of 20–55 μm. The lowest loss (several inverse centimeters) is characteristic of radiation with wavelength λ = 20 μm. The losses increase with the wavelength and reach a value of 150 cm^-1 at λ = 40 μm, which is almost independent of the waveguide layer thickness. For electromagnetic radiation with λ = 50 and 55 μm, a sharp (hundreds of times) decrease in the loss with an increase in the waveguide layer thickness is observed.     

Low loss integrated optical Y-branch

An antenna-coupled Y-branch with the advantages of low branching and short coupled length, and hence, compact size, is proposed. This structure is free from the critical fabrication requirements that are associated with the directional-coupler-type power dividers and 3 dB couplers. There is no need for any extra bending elements, hence, no bending loss, when this structure is used as a 3 dB coupler power divider of the Mach-Zehnder-type switch. Detailed theoretical analysis (both two-dimensional and three-dimensional) is carried out     

Radiation characteristics of multilayer periodic dielectric structures

Radiation characteristics of multilayer periodic dielectric structures are investigated by the method which combines the building block approach of multimode network theory with the rigorous mode matching procedure. The multilayer periodic structure is composed of uniform dielectric layers and single periodic layers. Two examples are given in this paper; first, radiation property of the double dielectric grating antenna is analyzed. The results indicate that the double dielectric grating antenna has relatively smaller dimensions than that of the single one. It is undoubtly of great importance in the case that the limitation of the weight and the volume of the system is strictly required. Secondly, some curved profile grating antennas are analyzed by combining the present method with the staircase approximation. In such a way, the effects of groove profile on the performance of the grating antennas are systemetically studied and some useful guidelines for the design of the dielectric grating antennas are thereby suggested.     

Radiation pattern synthesis of dielectric rod waveguide with many corrugations

The radiation pattern synthesis of dielectric rod waveguides with many corrugations is investigated. The guided waves are related in the form of a 2-port circuit and the radiation field is expressed by superposition of waves from the corrugations, so that the radiation pattern can be calculated in a very short time. This expression can be used in a genetic algorithm (GA) to seek the optimum arrangement of corrugations. Synthesized radiation patterns calculated using the 2-port circuit method compare well with patterns synthesised by the FDTD method. Conical beams and spherical sector beams can be synthesized. In the synthesized pattern, there are no unnecessary large lobes such as the grating lobe from a periodic waveguide. The experimental radiation patterns agree well with the synthesized patterns with small difference.     

A low-loss and compact waveguide Y-branch using refractive-index tapering

A new approach to an integrated Y-branch power splitter, useful for strongly guiding waveguide circuits, is proposed, fabricated and tested. The device uses adiabatic mode evolution by effective-refractive-index tapering to achieve a compact, low-loss geometry. Device performance is examined numerically by twoand three-dimensional beam propagation simulations. Y-branches with an overall length of /spl sim/330 /spl mu/m and losses of <0.2 dB are then fabricated in GaAs-AlGaAs. A compact and low-loss 1/spl times/4 power splitter incorporating this Y-branch is also described and demonstrated.     

Radiation properties of a planar dielectric waveguide loaded withconducting-strip diffraction grating

A dielectric planar waveguide periodically loaded with conducting strips is considered as a possible antenna for millimeter-wave range. We show that separating the grating from the waveguide leads to the reduction of radiative attenuation of the waveguided radiation and substantial narrowing of the angular spread of the diffracted radiation     

Y分支3维光波导横截面折射率分布

为了实现一个表达式同时反映Y分支光波导在纵横两方向上的折射率分布,通过对玻璃结构和离子交换过程进行分析,采用逆向分离变量法提出了基于横向和纵向两个方向折射率分布函数乘积的横截面折射率分布函数,并利用MATLAB软件对优化结果进行了编程模拟。利用Tl+-Na+离子交换法在BK7玻璃基底上制备了Y分支12型3维光波导,利用雅明干涉法对光波导横截面的折射率分布进行了测量。结果表明,利用改折射率分布函数模拟得到的Y分支光波导横截面折射率分布与雅明干涉法实验测得的结果吻合。该改进型折射率分布函数可以对Y分支光波导横截面折射率分布进行模拟,能准确快捷地对Tl+-Na+离子交换Y分支3维光波导横截面折射率分布进行重建。     

Effects of normal mode loss in dielectric waveguide directional couplers and interferometers

Theoretical arguments and experimental evidence are presented to show that the two fundamental normal modes of a coupled waveguide structure have different attenuations in traversing such a structure. The effects of this phenomenon on evanescent wave directional couplers and interferometers are derived. Parasitic effects in Mach-Zehnder and Sagnac interferometers utilizing directional couplers are described. An asymmetric output for the recently demonstrated all-single-mode fiber resonator is predicted and compared to experimental results. Some qualitative results are presented for integrated optic directional coupler switches.     

EBG结构在介质覆层波导缝隙相控阵中的应用

针对加载天线罩对于波导端头缝隙相控阵的天线性能和扫描盲点起到的恶化作用,提出了在阵面缝隙单元间加载EBG周期单元结构的方案,该方案结合了加载天线罩阵列缝隙之间的耦合特性以及EBG周期结构的抑制表面波特性,通过典型实例的数值仿真验证,消除了加载天线罩阵列的扫描盲点,展宽扫描范围,改善了天线阵的性能.     

Radiation and absorption losses of the whispering-gallery-modedielectric resonators excited by a dielectric waveguide

The scattering of a surface wave of a dielectric layer backed by a ground plane from the whispering-gallery-mode dielectric resonators is considered by use of the surface potential approach and analytical regularization. Efficient numerical algorithms have been developed with applications to the bandstop filter design. Transmitted and reflected power fractions and radiation and absorption losses are calculated and compared for two alternative field polarizations. The effect of excitation of the higher order modes of the waveguide is also studied     

Radiation characteristics of a waveguide excited dielectric sphere backed by a metallic hemisphere

The experimental results of the radiation characteristics of waveguide excited dielectric spheres backed by metallic hemispheres are reported. The test antenna consists of a dielectric loaded hemispherical horn excited by a circular waveguide. The test data have shown that such a structure produces a radiation pattern with low sidelobe levels, increased on-axis gain, and reduced 3 dB beamwidth as compared to a waveguide excited dielectric sphere of same diameter and an optimum horn having an aperture of identical cross section area. Also, it presents a low VSWR over the waveguide band.     

Nonradiative dielectric waveguide with perforated dielectric strip

The properties of a nonradiative dielectric waveguide with a dielectric strip perforated by a series of holes are described. The perforated guide can be used in instances where different wave impedances are desired, in addition to where different propagation velocities are needed without resorting to the use of physically different materials.     

Miniaturized dielectric waveguide filters

Design techniques for a new class of integrated monolithic high-permittivity ceramic waveguide filters are presented. These filters enable a size reduction of 50% compared to air-filled transverse electromagnetic filters with the same unloaded Q-factor. Designs for Chebyshev and asymmetric generalised Chebyshev filter and a diplexer are presented with experimental results for an 1800 MHz Chebyshev filter and a 1700 MHz generalised Chebyshev filter showing excellent agreement with theory.     

Radiation loss coefficients of asymmetric dielectric waveguides with shallow sinusoidal corrugations

Kiselev [10] has solved the boundary equations for an asymmetric slab waveguide with a shallow sinusoidal corrugation, and derived explicit, closed expressions for the TE radiation loss coefficients of various waveguide geometries. For many practical applications in integrated optics, the Rayleigh assumption justifying the boundary-matching procedure and the approximations of linear perturbation analysis employed in this derivation are both satisfied. We have extended this procedure to TM modes and found that the expressions for both TE and TM modes in all of the geometries so treated agree identically with those derived by coupled-mode theory. The dependence of the TM radiation loss coefficient in each waveguide geometry on the grating period, radiation angle, refractive index profile, and mode polarization is illustrated graphically, and compared with its TE counterpart.     

Radiation losses of tapered dielectric waveguides: a finitedifference analysis with ridge waveguide applications

The finite-difference third-order simplified wave equation method is used to study the radiation losses of optical waveguides with step (abrupt) and parabolic tapers, including the radiation losses of the tapered ridge waveguides used as electro-optic phase modulators for tuning the frequencies of infrared lasers. The radiation losses of the parabolic taper given by Burns et al. is found to be under 5%. The results of a step taper are compared with Marcuse's; and found to be in good agreement. The numerical results are also compared with those from the coupled wave equations used by Sporloder and Unger     

Corporate feed in nonradiative dielectric waveguide

The development of a corporate feed for application to antennas fed from a nonradiative dielectric (NRD) waveguide is described. A feed was constructed and tested, and its performance evaluated by allowing the unterminated circuit to radiate as an antenna