Anisotropic Slab Waveguides Research Articles

Conical Swiss Roll Metamaterial Application for Slow-Light Waveguides

The framework for designing and fabricating a slow-light waveguide structure with conical Swiss roll metamaterial core at Terahertz frequencies has been carried out in this article. In the earliest work, theoretical backgrounds based on Maxwell’s equations have been developed for anisotropic single-negative permeability slab waveguides and anisotropic metamaterial slab waveguides. Subsequently, simulation results fulfilled by the MATLAB programming tool verify extremely low group velocities in the aforementioned slab waveguides in the Terahertz regime frequency. A volumetric conical Swiss roll metamaterial has been proposed as a practical achievement for slow-light waveguides. Dispersion characteristics of the electromagnetic waves in the proposed conical Swiss roll metamaterial have been investigated using the CST simulation tool in Terahertz frequencies. Furthermore, a 2-D dispersion diagram fulfilled by CST and MATLAB validates highly electromagnetic field concentration as well as the presence of backward waves in the conical Swiss roll configuration.

Effect of the electric field induced birefringence on the slab waveguide evanescent-wave sensor sensitivity

We have investigated the potential of using the E-field induced birefringence for improving the sensitivity of uniaxial anisotropic slab waveguide sensor based on evanescent wave interactions. LiNbO3 waveguide core was used as an example. We have calculated the sensor sensitivity formulas for the two kinds of modes propagating simultaneously in the waveguide sensor. In our study, we have distinguished between two different cases. The first case when the electric field is applied along the optic axis (+c) of the LiNbO3 wave guiding film (positive electric field); the second case when the electric field is applied opposite to the optic axis (−c) of such uniaxial crystal (negative electric field). The obtained results showed that, for positive electric field, increasing the electric field induces an increasing of the total anisotropy which causes decreasing on sensor sensitivity. However, for negative electric field, the increase of absolute values of negative electric field induces a decrease of the total anisotropy, the latter increases the sensor sensitivity. On the other hand, the study of the physical parameters on the sensor sensitivity showed that, to maximize the sensor sensitivity, it is advisable to use isotropic substrate that has a refractive index as closer as possible to the measurand index.

Optical modes in slab waveguides with magnetoelectric effect

Optical modes in anisotropic slab waveguides with topological and chiral magnetoelectric effects are investigated analytically, by deriving the closed-form characteristic equations of the modes and hence computing the dispersion-diagrams. In order to compute the characteristic equations, a vector-potential approach is introduced by incorporating a generalized Lorentz gauge, and the Helmholtz equations are derived correspondingly. It will be shown that the formation of the complex modes and hybridization of the optical modes in such slab waveguides is inevitable. Moreover, when the tensorial form of the permittivity in the waveguide allows for a hyperbolic dispersion, complex transition from the photonic kinds of modes to the plasmonic modes is expected.

Dipole radiation within one-dimensional anisotropic microcavities: a simulation method

We present a simulation method for light emitted in uniaxially anisotropic light-emitting thin film devices. The simulation is based on the radiation of dipole antennas inside a one-dimensional microcavity. Any layer in the microcaviy can be uniaxially anisotropic with an arbitrary orientation of the optical axis. A plane wave expansion for the field of an elementary dipole inside an anisotropic medium is derived from Maxwell's equations. We employ the scattering matrix method to calculate the emission by dipoles inside an anisotropic microcavity. The simulation method is applied to calculate the emission of dipole antennas in a number of cases: a dipole antenna in an infinite medium, emission into anisotropic slab waveguides and waveguides in liquid crystals. The dependency of the intensity and the polarization on the direction of emission is illustrated for a number of anisotropic microcavities.

Experimental and theoretical analysis of THz-frequency, direction-dependent, phonon polariton modes in a subwavelength, anisotropic slab waveguide

Femtosecond optical pulses were used to generate THz-frequency phonon polariton waves in a 50 micrometer lithium niobate slab, which acts as a subwavelength, anisotropic planar waveguide. The spatial and temporal electric field profiles of the THz waves were recorded for different propagation directions using a polarization gating imaging system, and experimental dispersion curves were determined via a two-dimensional Fourier transform. Dispersion relations for an anisotropic slab waveguide were derived via analytical analysis and found to be in excellent agreement with all observed experimental modes. From the dispersion relations, we analyze the propagation-direction-dependent behavior, effective refractive index values, and generation efficiencies for THz-frequency modes in the subwavelength, anisotropic slab waveguide.

Anisotropic Left-Handed and μ-Negative Slab Waveguides: Physics and Device Applications

We study the properties of various anisotropic left-handed slab waveguides. The analysis is extended to anisotropic μ-negative slab waveguides. The possible existence of the plasmon modes in various anisotropic slab waveguide configurations is discussed. An FDTD program is developed to investigate the potential device applications of these anisotropic structures. A new signal detector and a two-channel harmonic separator multiplexer are designed employing the μ-negative slab waveguide.

Reflectivity properties of an anisotropic slab waveguide with isolated substrate

The scattering properties for both TE and TM modes of an abruptly ended two-layered slab waveguide with anisotropic core and isolated substrate are examined by an improved iteration technique, which is based on the integral equation method with accelerating parameters. The relative dielectric constants of the core for the three Cartesian directions are considered to be different, but cases with isotropic core are also considered. The electric field distribution on the terminal plane and the reflection coefficients of the dominant TE and TM guided modes, as well as the near-field distribution and the far-field radiation pattern, are computed, while numerical results are presented for several cases of the core anisotropy.

An efficient method for measuring the parameters of single‐mode anisotropic slab waveguides using the prism‐coupling technique

AbstractAn efficient method for measuring the parameters of anisotropic slab waveguides is presented in this paper. This method can be used to measure the parameters of single‐mode anisotropic slab waveguides. The measured results show that the errors of the refractive indices are within 4.2 × 10−4. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 575–580, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21234

Fundamental modal phenomena on isotropic and anisotropic planar slab dielectric waveguides

The characteristic interactions of discrete modes supported by planar isotropic and anisotropic dielectric slab waveguides are analyzed using singularity and critical point theory, leading to a rigorous and complete explanation of all modal interactions. Complex frequency-plane singularities associated with modes on isotropic waveguides are identified and discussed, and the absence of mode coupling is proven. For an anisotropic planar waveguide having an arbitrarily oriented optical axis, it is shown that mode coupling is controlled by the presence of an isolated Morse critical point (MCP) accompanied by a pair of complex-conjugate frequency-plane branch points. The interaction of space-wave leaky modes on a grounded anisotropic slab is studied by investigating the evolution of complex frequency-plane branch point singularities as the orientation of the optical axis varies. The general theory is presented, and numerical results are provided for some specific waveguides.

Anisotropic surface relief diffraction gratings under arbitrary plane wave incidence

A modal method is used for the analysis under oblique incidence of a diffraction grating made of anisotropic material. The problem is studied viewing the structure as the cascade of junctions between periodic arrays of anisotropic slab waveguides with the same period and different heights. This diffraction problem is formulated in terms of an integral equation that enforces the continuity of the transverse magnetic field at the junction. The unknown is the transverse electric field at the junction. It is possible to use also another formulation, where the role of the two fields is exchanged. The kernels of these equations are the relevant Green's functions, which are expressed in terms of eigenfunction expansions. The determination of the modes of the various regions composed of arrays of anisotropic dielectric slabs has been carried out by the method of spectral elements, whereby the field components are represented in a polynomial basis and the original differential eigenvalue problem is converted into an algebraic one. The integral equation is solved numerically by the method of moments and each junction is characterized by its generalized scattering matrix (GSM). Finally, the diffraction efficiencies of the grating are obtained by combining the various GSM's.

Coupling efficiency of two anisotropic single‐mode slab waveguides butt‐joined via a gap

AbstractThe fundamental characteristics of the coupling efficiency between two anisotropic slab waveguides with different configurations butt‐joined via a gap are analyzed in the case of a TM mode incidence by means of a single‐mode slab waveguide model made of equatorial dielectric tensor. the electromagnetic field in the gap is represented by a combination of the forward elementary plane wave propagating from the incident side to the output waveguide and the backward elementary plane wave propagating in the opposite direction.By applying the boundary conditions, the power transmission and reflection coefficients in the guided‐wave system are computed. Further, the effects of the lateral misalignment and inclination between the wave‐guides and the index of refraction and spacing of the gap on the coupling efficiency are studied based on the numerical results. an optimum condition to maximize the coupling efficiency is obtained.

Transmission and Reflection at Butt Joints between Isotropic and Anisotropic Single-Mode Slab Waveguides

Transmission and reflection properties are studied for a butt joint between an isotropic slab waveguide and an anisotropic one consisting of uniaxial crystalline material which has the optical axis in the plane defined by the propagation axis and the normal of the waveguide surface. The effects of axial displacement and angular misalignment are discussed on the basis of numerical results obtained from two different formulas: one is derived from the boundary condition together with the modal orthogonality and the other is based on the simple overlap integral of modal profiles. It is confirmed that the simple formula in terms of the overlap integral is applicable to the characterization of butt joints involving anisotropic waveguides.

Coupling efficiency of butt-joined isotropic and anisotropic single-mode slab waveguides

Studied is the effect of axial displacement and angular misalignment on the power-coupling efficiency of a butt-joint between an isotropic and an anisotropic single-mode slab waveguide. The power-coupling coefficient is formulated by means of the boundary conditions at the interface of the butt-joint and the orthogonality relations between the modes in the outgoing waveguide. It is found from the numerical results that proper amounts of angular misalignment and axial displacement remarkably suppress transmission losses when the material coordinate system of the anisotropic waveguide is not aligned with its waveguide coordinate system in the plane defined by the propagation axis and the normal of the waveguide surface. >

Radiation loss due to step discontinuities in symmetric biaxially anisotropic slab waveguides

This paper is an extension of previous work [1] dealing with guided wave propagation through step discontinuities in anisotropic slab waveguides which focused on the radiated fields only. As opposed to the earlier work, this paper deals with radiation power losses suered by a guided mode incident on the junction, with calculation carried out by an approximate perturbation technique. In addition, the radiation mode solutions to Maxwell's equations in a symmetric biaxially anisotropic slab waveguide are presented for both odd and even symmetries. Characteristics of anisotropic guides are discussed and compared to those of their conventional isotropic counterparts.

Far‐field radiation from step junctions in biaxially anisotropic slab waveguides

AbstractIn this article far‐field radiation properties of step discontinuities on biaxially anisotropic slab waveguides are examined. The stationary phase method is applied to obtain the asymptotic form of the far‐field expressions, which are derived based on the transmission coefficient of the radiation mode. The analysis yields data that agree well with those previously published for special cases of isotropic slabs. The newly calculated results for far‐field radiation patterns of step junctions between biaxially anisotropic waveguides are presented for several combinations of tensor element parameters.

Anisotropic guided-wave diffraction by interdigitated electrode-induced phase gratings

The diffraction of a pure guided mode in a uniaxial anisotropic slab waveguide by a phase grating which is induced by a voltage applied to interdigitated electrodes over the waveguide is analyzed. A pure guided mode is decomposed into four plane wave components (two ordinary and two extraordinary), which are not phase matched on the boundary between the waveguide and the grating. Thus the diffraction of a pure guided mode may be decomposed into the diffraction of four plane waves. Three-dimensional vector rigorous coupled-wave diffraction analysis of anisotropic gratings with anisotopic external regions is used to treat the diffraction of each plane wave component of the pure guided mode. Geometrical and phase/amplitude requirements are identified for the diffracted waves to constitute a guided mode. Diffracted mode efficiencies and Bragg conditions are calculated. Optic axis orientations for efficient diffraction are identified. Example calculations are presented for lithium niobate waveguide Givens rotation devices, and herringbone multiplier structures including a favorable comparison with experimental results.

Scalar finite element analysis of electrooptic modulation in diffused channel waveguides and poled waveguides in polymer thin films

Electrooptic modulation with diffused channel waveguides is analyzed by utilizing the approximate scalar finite element approach developed for anisotropic asymmetric slab waveguides. The interaction of the applied electric fields with the optical fields is calculated over the 2-D finite element mesh, and the direct calculation of the waveguide eigenmodes provides the electrooptic changes in the propagation wavenumbers. Applications of this simplified finite element approach to arbitrary index profiles and fields are illustrated for both titanium-indiffused LiNbO(3) and poled waveguides in polymer thin films.

An exact method for analysing light propagation in anisotropic inhomogeneous optical waveguides

A method is proposed for finding field distributions and dispersion characteristics of an effective refractive index in anisotropic graded-index slab waveguides with arbitrary parameters of the waveguide layer and the substrate's optical anisotropy.

Approximate scalar finite-element analysis of anisotropic optical waveguides

An approximate scalar finite-element program for the analysis of anisotropic optical waveguides with a diagonal permittivity tensor is described. The accuracy of the method has been checked by calculating the eigenmodes of two-dimensional, anisotropic asymmetric slab waveguides. The results obtained for a channel waveguide embedded in LiNbO3 agree well with the results of the earlier vectorial finite-element method.

Network Representation and Transverse Resonance for Layered Anisotropic Dielectric Waveguides

First, the matrix wave impedance in an unbounded uniaxial lossless dielectric material is determined. Next, the transformation properties of the input impedance of a terminated anisotropic layer are established. It is then demonstrated that the boundary conditions in an anisotropic dielectric slab waveguide lead to a generalized transverse resonance condition involving the previously obtained matrix input impedances. Network equivalent representations are given for waveguides fabricated with dielectrics in polar and longitudinal orientations. The results show that a circuit approach to the analysis and design of planar anisotropic dielectric waveguides is feasible and practicable.