Magnetic Waves Guided by a Linearly Tapered Yig Film

A quasi-optical treatment is given for the dispersion relation and the group delay time of a magnetic wave guided by a YIG film having a weak linear taper in its thickness in the propagation direction of the guided magnetic wave. This treatment has 1) confirmed the intuitive results in which the local value of the thickness is used for the tapered film, 2) indicated the frequency regions of validity of the intuitive results, and 3) revealed interesting features of the wavenormal and ray directions inside a YIG film.     

Investigating nonlinear propagation in dielectric slab waveguides

A numerical method is employed to analyze the TE-wave propagation in Kerr-like nonlinear dielectric waveguides in which a nonlinear film is sandwiched between two linear media. The dispersion curves dependent on the magnitude of the electric field are obtained. All the results can be used in future investigations of devices composed of nonlinear dielectric slab structures     

Nonlinear pulse propagation in a monomode dielectric guide

We derive the nonlinear wave equation for an envelope of an electromagnetic wave in a monomode dielectric waveguide. Concrete examples are given for a single-mode optical fiber where the coefficients of resultant nonlinear Schrödinger equation with higher-order dispersion and dissipation (both linear and nonlinear) are given in terms of properties of the eigenfunction of the guided wave as well as of the material nonlinearity and dispersion. Using a newly-developed perturbation method, we show that the higher-order dispersions (linear and nonlinear) perserve the profile of a single soliton but to split up a boundNsoliton (N geq 2) into individual solitons with different heights which propagate at different velocities. We also show that the higher-order nonlinear dissipation due to the induced Raman effect downshifts the carrier frequency of a single soliton in proportion to the distance of propagation and to the fourth power of the soliton amplitude.     

自聚焦介质波导中的新型导波

本文给出了导波层为自聚焦介质平板波导波方程的特殊精确解,得到了具有非线性导波层的波导归一化色散方程及场分布,并对得出的结果进行了讨论。     

TM-polarized nonlinear guided waves in multilayer systems

The ability of various multilayer systems to support TM-polarized nonlinear guided waves is studied. A flexible numerical technique which includes the proper consideration of the nonlinear crossing conditions is used to calculate the field profiles and derive the dispersion relations. The fundamentals of the model are described, and the algorithm is applied to several nonlinear film configurations. For the sake of comparison with the finite-element method, a single linear film, embedded between two nonlinear materials, is treated. A three-film unit cell, consisting of a high-index linear film, sandwiched between two low-index nonlinear, ones is considered. This is the elementary unit cell of a composite geometry, a ten-unit-cell superlattice, which is then studied. It is found that unlike TE-polarized nonlinear guided waves in multilayer systems, the TM waves reveal a distinct power maximum. The inclusion of saturation effects in the analysis is straightforward     

The nonlinear self-defocusing electromagnetic surface waves in a metalised ferrite film

The dispersion relations for TE s-polarized nonlinear electromagnetic surface waves guided by a metallised ferrite film, surrounded by a nonlinear self-defocusing dielectric cover with intensity dependent refractive indices have been computed. Numerical results are also illustrated to show the propagation characteristics for different values of the film thickness, and at a fixed value of the dielectric-ferrite interface nonlinearity. It has been found that the surface waves exist in both directions of propagation, where the external field is applied. The propagation of these waves is non-reciprocal, and has a resonant interaction in the reverse direction. The power flow carried by the structure has also been calculated for different values of the slab thickness. The non-reciprocity has also been obsorved, and the power flow level can been controlled by the film thickness. of semi-infinite gyromagnetic and nonlinear media². If we increase the operating frequency, the power flow level changes at a fixed film thickness, forβ ≥ 0 and forβ ≤0 as in Figs.4. There exist a limited eigenvalues (solutions) with f=17.8GHz forβ ≥ 0, and for different values of the operating frequency forβ ≤ 0. So the eigenvalues and the power flow level can be varied as the operating frequency is tunned. At f=17.8GHz forβ ≥ 0, as in fig.4b, to some value of the power flow there correspond two propagation wave index, which are being related to bistable states of nonlinear surface. All the above mentioned behaviours exhibit the characteristics of microwave switches, isolators, and limiters and could be used in some experimental applications in Microwave Engineering Technology. The other parameters effects as the magnetic field, magnetization, types of ferrite etc. on the dispersion characteristics and the power flow are now under consideration.     

Nonlinear waves in saturable self-focusing thin films bounded bylinear media

Nonlinear guided wave behavior in the symmetric and asymmetric versions of an optical waveguide is studied. The waveguides are made to cut off at low field intensities by a step-index decrement in the dielectric constant of the film relative to those of the bounding media. The influence of this decrement on solutions of the TE₀ mode is calculated. The mode index variation of the asymmetric solution in the symmetric waveguide is shown to depend strongly on the index decrement as well as the saturation level. By making the media bounding the film have sufficiently different dielectric constants, only one solution is shown to be obtainable. This solution is followed both on the locus diagram relating the field intensities on the film boundaries and on dispersion plots     

非线性介质膜波导中高阶TE模的色散特性

用微扰方法对非线性波动方程求解,导出了各阶近似下非线性介质膜波导中高阶TE模的色散方程和截止波长。研究了高阶TE模的色散特性。计算结果表明,具有功率激发阈值的高阶模的一个传播功率可能对应两个不同的传播常数,具有光学开关的特性。     

Unified nonlinear waveguide dispersion equations without spuriousroots

Analysis is made of the behavior of transverse electric (TE) waves in an optical waveguide comprising a nonlinear film sandwiched between two semi-infinite linear media. Unified expression of dispersion equation is presented for all different nonlinear waveguides, which could have any possible linear dielectric profile, and comprise a nonlinear film with either self-focusing or self-defocusing nonlinearity. This new dispersion equation offers simple numerical calculations and avoids the appearance of spurious roots     

Field theory of dielectric Cherenkov maser

The effect of three-dimensional perturbed velocity and three-dimensional perturbed current density on the beam-wave interaction of dielectric Cherenkov maser is analysed by use of the self-consistent linear field theory. Three distinct cases are considered. First, the propagation of the electron beam in an annular dielectric liner enclosed by a loss-free conducting wall is investigated. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. It's clearly shown that the instability of the interaction results from the coupling of the TM mode in the dielectric lined slow-wave waveguide to the beam mode via the electron beam. And the coupling is proportional to the density of the beam. The growth rate of the wave produced by the electron beam are obtained. Then, the case of a relativistic electron beam guided by a longitudinal magnetic field in the same slow-wave structure is examined. The motion of electrons could be approximated to be one-dimensional when the simultaneous condition of the beam-wave interaction of dielectric Cherenkov maser is satisfied. Finally, the effect of the background plasma on the instability of the beam-wave interaction is studied.     

非线性平板介质波导传输特性的网络分析

本文提出了分析包含非线性介质的层状介质波导特性的等效传输线方法。通过把线性和非线性介质分别用等效传输线表示,从而把非线性介质这一复杂的电磁场问题等价成一个电路问题求解。其本征方程可以利用横向谐振原理得到。本文最后分析了层状介质波导包含饱和和非饱和非线性介质时TE模的传播功率与归一化传播常数之间的关系。所获得的结果与有关文献符合得相当好。     

Analysis and Calculations on Dispersion Relation and Coupling Resistance of Periodic Plasma-Cavities

The plasma tensor dielectric permittivity and electromagnetic field accurate expressions in the external axial magnetic field are obtained from the Maxwell’s equations and the double component plasma particle linear movement equations. Further, the flux of energy inside the plasma-cavity drift channel is presented. Based on them, some of the property of cavity passband dispersion and coupling resistance of plasma-filled coupled-cavities slow wave structure in different plasma density and magnetic field conditions is analyzed according to the numerical calculation.     

Modal analysis of nonlinear propagation in dielectric slabwaveguide

In this paper we present a study of nonlinear guided propagation based on the development of the actual electromagnetic field in terms of the modes of a linear dielectric guide. This approach permits in principle to consider propagation over finite lengths of waveguide of general nonuniform nonlinearity, with arbitrary excitation at a finite location and to retain the second derivative term that is neglected in the usual Schrodinger equation approximation to the wave equation     

A Perturbation Method for Complex Root Finding of Nonlinear Electromagnetic Waves

Aspects of the perturbation method are presented and implemented on the analytic function of the complex variable for the propagation of nonlinear electromagnetic surface guided by a thin film. The behavior of nonlinear TE waves guided by asymmetrical dielectric thin film, bounded by a generalizes nonlinear substrate with a permittivity of the form ? ～ | E |^δ is analyzed. The complex roots, which correspond to the propagation and attenuation coefficient are obtained and discussed.     

Propagation properties of ferromagnetic insulator guide

In order to realize new ferrite planar devices for applications at millimeter-wavelength frequencies, the authors have developed nonreciprocal ferrite devices schemes for incorporating ferromagnetic layers in dielectric insulator guide geometries. Their research program involves both the calculation and the measurement of device characteristics. For the calculation, a method of effective permeability, in which the permeability is a tensor, is introduced to characterize the ferrite material. The propagation properties of the insular guide are calculated by using a single-mode approach. The calculated results for dispersion, dielectric, and conductivity losses show resonant behavior with the application of a magnetic bias field for a guide configuration in which the ferrite replaces the insular dielectric. Ferrite phase shifters, filters, isolators, and circulators are potential applications of this guide configuration. For the experimental part of the study, wave dispersion and attenuation were measured in a purely dielectric insular guide from 26.5 to 40GHz. In addition to these experiments wave attenuation was measured as a function of magnetic bias field for the case where a hexagonal ferrite platelet was mounted on the ground plane near the insulator guide. General agreement is found between calculated and measured attenuation     

Pulse propagation in a nonlinear dielectric slab waveguide

The evolution of an optical pulse in a single-mode, step index dielectric slab waveguide which is characterized by an intensity dependent dielectric function in the core and cladding regions is treated by means of differential equation techniques. A cubic order non-linearity is considered. The electromagnetic field distribution in the slab waveguide region satisfies a non-linear wave equation. This field can be represented in terms of even TE guided modes with a slowly varying envelope amplitude function. Then using the well known approximation, based on the slowly varying character of the amplitude function, a non linear partial differential equation is obtained for the amplitude function. As the coefficients of this equation depend on the distance across the transverse direction X, an averaging technique over x is applied to reduce the nonlinear partial differential equation into a form that is easily transformed to the so-called non-linear Scroedinger differential equation. This equation is then attacked by means of the well known Inverse Scattering method in the case of reflection less potentials. The single and double soliton solutions are obtained explicitly for a single-mode slab waveguide. Finally numerical results are presented in the time domain.     

Finite-element formalism for nonlinear slab-guided waves

A unified computer-aided numerical approach, based on the finite-element method, is developed for analyzing optical waves guided by dielectric slab waveguiding structures with arbitrary nonlinear media. In the formulations, both TE and TM polarizations are considered. For the TM case, the biaxial nature of nonlinear refractive index is considered without any approximation. Numerical results are presented for nonlinear TE and TM waves propagating in symmetric slab waveguides. The dependence of dispersion relations on the refractive-index profile of the film is examined     

Guided waves in nonlinear saturable self-focusing thin films

Novel features of nonlinear guided waves in saturable thin-film waveguides are obtained. It is shown that the presence of saturation can strongly modify the behavior of TE waves in comparison to films having a Kerr-like nonlinearity. The fundamental mode index is seen to become bounded by limits determined by the saturation level. The example of symmetric waveguide is analyzed and the dispersion plots of symmetric and asymmetric solutions are obtained. It is shown that only the symmetric solution can be followed at high film interface intensity and that the asymmetric solution becomes absent at low saturation levels.     

单纯形法在非线性光波导传播特性分析中的应用

简要介绍了优化理论中的单纯形方法,并且应用到求解介质非线性光波导的色散方程。文中计算了非线性光波导传输特性的2个实例,1）非对称3层平板波导,由线性衬底、克尔型芯区和线性包层（LNL）组成;2）对称3层平板波导,由克尔型包层、衬底及线性芯区组成（NLN）。数值结果表明,非线性光波导的色散方程很困难求解时,单纯形方法对于分析非线性光波导的传输特性简便而且有效。     

Exact analytic solutions to the nonlinear wave equation for asaturable Kerr-like medium: modes of nonlinear optical waveguides andcouplers

Exact analytic solutions to the nonlinear wave equation for a lossless saturable Kerr-like medium are found. The nonlinearity is an intensity-dependent refractive index which saturates according to the model n²=n₀²±a|E|²/(1+b|E| ²). The solutions to the wave equation are used to determine the TE power-dependent dispersion relations, and therefore the guided modes, of a single waveguide structure and of a directional coupler whose coupling medium is the nonlinear saturable material. Although the interaction between the sinh- and cosh-like modes of the coupler, and therefore the coupling length, is not treated in this work, it is shown that the critical power, defined in the literature to be the level of input power above which 100% of the power cannot be switched between the guides of a coupler, is a mathematical misinterpretation in both saturable media as well as in nonsaturable Kerr media. The absence of a critical power in single waveguide structures is also demonstrated. Parameters of GaAs-based waveguides and of a GaAs-GaAlAs MQW coupling medium are used in the numerical analysis