Mode -pairs in the multi-layer waveguide are defined relative to a prescribed mode in a single layer as being synchronized and having nearly perfect wavestructure matching. Only a limited number of mode -pairs exist, and each has a unique frequency range. A hybrid model based on semi-analytical finite elements and the normal mode expansion is implemented to assess mode conversion at a step transition in a waveguide.
The model results indicate that synchronism and wavestructure matching is associated with energy transfer through the step transition, and that the energy of an incident wave mode in a single layer is transmitted almost entirely to the associated mode -pair, where one exists. This analysis guides the selection of incident modes that convert into transmitted modes and improve adhesive joint inspection with ultrasonic guided waves.
Analytical relation between effective mode field area and waveguide dispersion in microstructure fibers. For optical fibers exhibiting a radially symmetric refractive index profile, there exists an analytical relation that connects waveguide dispersion and the Petermann-II mode field radius. We extend the usefulness of this relation to the nonradially symmetric case of microstructure fibers in the anomalous dispersion regime, yielding a simple relation between dispersion and effective mode field area. Assuming a Gaussian mode distribution, we derive a fundamental upper limit for the effective mode field area that is required to obtain a certain amount of anomalous waveguide dispersion.
This relation is demonstrated to show excellent agreement for fiber designs suited for supercontinuum generation and soliton lasers in the near infrared. A comparison was made of the calculated and measured radiative losses suffered by the fundamental and first higher modes in real waveguide structures with a depressed cladding. It was found that in determination of the operating range of single- mode waveguides with a depressed cladding it is essential to allow not only for the increase in the losses due to leaking of the fundamental HE11 mode at long wavelengths, but also for the shift of the cutoff wavelength of the first higher HE21 mode for shorter wavelengths.
Circular free-electron laser. A high efficiency, free electron laser utilizing a circular relativistic electron beam accelerator and a circular whispering mode optical waveguide for guiding optical energy in a circular path in the circular relativistic electron beam accelerator such that the circular relativistic electron beam and the optical energy are spatially contiguous in a resonant condition for free electron laser operation. Both a betatron and synchrotron are disclosed for use in the present invention. A free electron laser wiggler is disposed around the circular relativistic electron beam accelerator for generating a periodic magnetic field to transform energy from the circular relativistic electron beam to optical energy.
Waveguide modes of 1D photonic crystals in a transverse magnetic field. We analyze waveguide modes in 1D photonic crystals containing layers magnetized in the plane. It is shown that the magnetooptical nonreciprocity effect emerges in such structures during the propagation of waveguide modes along the layers and perpendicularly to the magnetization. This effect involves a change in the phase velocity of the mode upon reversal of the direction of magnetization.
This is associated with asymmetry of the dielectric layers contacting with the magnetic layer in the former case. This effect is important for controlling waveguide structure modes with the help of an external magnetic field.
Wave attenuation and mode dispersion in a waveguide coated with lossy dielectric material. The modal attenuation constants in a cylindrical waveguide coated with a lossy dielectric material are studied as functions of frequency, dielectric constant, and thickness of the dielectric layer.
A dielectric material best suited for a large attenuation is suggested. Using Kirchhoff's approximation, the field attenuation in a coated waveguide which is illuminated by a normally incident plane wave is also studied.
Candra Kurniawan, S.Si
A vertically-coupled whispering gallery mode WGM resonator optical waveguide , a method of reducing a group velocity of light, and a method of making a waveguide are provided. The vertically-coupled WGM waveguide comprises a cylindrical rod portion having a round cross-section and an outer surface. First and second ring-shaped resonators are formed on the outer surface of the cylindrical rod portion and are spaced from each other along a longitudinal direction of the cylindrical rod.
The first and second ringshaped resonators are capable of being coupled to each other by way an evanescent field formed in an interior of the cylindrical rod portion. Recent developments in the design of metamaterials with an effective negative index suggest that this waveguide could operate in the infrared region of the spectrum. Dispersion of TE modes in slab waveguides with reference to double heterostructure semiconductor lasers.
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The group index for TE modes in an asymmetrical slab waveguide is investigated, and a simple analytical expression is derived. It is shown that the product of the phase and group indices is related to the power fraction in each of the three layers of the waveguide. The results are of interest in the analysis of double heterostructure semiconductor lasers. Theoretical and experimental results for lasers emitting at 1. Coupling losses between standard single- mode fibers and rectangular waveguides for integrated optics.
The butt-coupling loss between different tapered rectangular waveguides and a standard single- mode optical fiber has been calculated. Losses as low as 0. The fabrication tolerances are such that practical devices with coupling losses below 0. Method of adiabatic modes in studying problems of smoothly irregular open waveguide structures. Basic steps in developing an original method of adiabatic modes that makes it possible to solve the direct and inverse problems of simulating and designing three-dimensional multilayered smoothly irregular open waveguide structures are described.
A new element in the method is that an approximate solution of Maxwell's equations is made to obey 'inclined' boundary conditions at the interfaces between themedia being considered. These boundary conditions take into account the obliqueness of planes tangent to nonplanar boundaries between the media and lead to new equations for coupled vector quasiwaveguide hybrid adiabatic modes.
The efficiency of the method is demonstrated by considering the example of numerically simulating a thin-film generalized waveguide Lueneburg lens. Novel spot size converter for coupling standard single mode fibers to SOI waveguides. We have designed and numerically simulated a novel spot size converter for coupling standard single mode fibers with Simulations based on the eigenmode expansion method show a coupling loss of 0. The waveguides are designed to collectively support a single degenerate mode for TE and TM polarizations. This guided mode features a large overlap to the LP01 mode of standard telecom fibers.
The shapes of SiOxNy and SOI tapers are optimized to minimize coupling loss and structure length, and to ensure adiabatic mode evolution along the structure, thus improving the design robustness to fabrication process errors.
A tolerance analysis based on conservative microfabrication capabilities suggests that coupling loss penalty from fabrication errors can be maintained below 0. The proposed spot size converter is fully compliant to industry standard microfabrication processes available at INO. Single- mode plasmonic waveguiding properties of metal nanowires with dielectric substrates. Single- mode plasmonic waveguiding properties of metal nanowires with dielectric substrates are investigated using a finite-element method.
Au and Ag are selected as plasmonic materials for nanowire waveguides with diameters down to 5-nm-level. Typical dielectric materials with relatively low to high refractive indices, including magnesium fluoride MgF2 , silica SiO2 , indium tin oxide ITO and titanium dioxide TiO2 , are used as supporting substrates. Basic waveguiding properties, including propagation constants, power distributions, effective mode areas, propagation distances and losses are obtained at the typical plasmonic resonance wavelength of nm.
Compared to that of a freestanding nanowire, the mode area of a substrate-supported nanowire could be much smaller while maintaining an acceptable propagation length. For example, the mode area and propagation length of a nm-diameter Ag nanowire with a MgF2 substrate are about 0. The dependences of waveguiding properties on geometric and material parameters of the nanowire-substrate system are also provided.
Our results may provide valuable references for waveguiding dielectric-supported metal nanowires for practical applications. Investigation for all polarization conversions of the guided- modes in a bending waveguide. In this work, a new solution to the partial differential Maxwell equations is first derived to investigate all polarization conversions of the transverse and the longitudinal components of guided- modes in a bending waveguide.
Then, for the silica- waveguides , the polarization conversion efficiencies are numerical calculated and a significant finding is that the transverse-longitudinal polarization conversion efficiency is much higher than that of transverse-transverse polarization conversion.
Furthermore, the dependences of all the conversion efficiencies on waveguide parameters are found. A numerical solution for time-harmonic electromagnetic fields in two-port passive radio frequency RF devices has been developed, implemented in a computer code, and validated. Vector finite elements are used to represent the fields in the device interior, and field continuity across waveguide apertures is enforced by matching the interior solution to a sum of waveguide modes.
Consequently, the mesh may end at the aperture instead of extending into the waveguide. The report discusses the variational formulation and its reduction to a linear system using Galerkin's method. It describes the computer code, including its interface to commercial CAD software used for geometry generation. It presents validation results for waveguide discontinuities, coaxial transitions, and microstrip circuits.
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They demonstrate that the method is an effective and versatile tool for predicting the performance of passive RF devices. A system of coupled single- mode waveguides with the number M of guided modes lower than the number N of single- mode waveguides is studied. Leaky modes in this system are investigated in detail.
It is shown, in particular, that these modes can be excited by light incident on the side surface of the system when the reflection coefficient vanishes. It is found that the angular dependence of the coefficient of reflection from the side surface of the system can be used to refine the dispersion curve for leaky modes.
It is shown that light incident at a grazing angle can propagate in the system in the direction considerably different from the propagation direction of a beam incident from a substrate, even in the case of a small difference in the refractive indices. Inhibiting the TE1- mode diffraction losses in terahertz parallel-plate waveguides using concave plates.
We present numerical and experimental results on inhibiting diffraction losses associated with the lowest order transverse electric TE1 mode of a terahertz THz parallel-plate waveguide PPWG via the use of slightly concave plates. We find that there is an optimal radius of curvature that inhibits the diffraction for a given waveguide operating at a given frequency. We also find that introducing this curvature does not introduce any additional group-velocity dispersion. Passive fiber alignment to single- mode plastic waveguides fabricated by injection molding.
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Passive fibre- waveguide coupling is a promising alternative to expensive active coupling in single- mode fibre-optics. The idea to utilize replication techniques in transparent polymeric materials for waveguide and alignment structure fabrication has led to the SIGA-process Silizium, Galvanik und Abformung which allows a cost effective production of low loss polymer waveguides in the near IR. Major difficulties in passive fibre coupling are caused by the high lateral alignment accuracy of about 1 micrometer in fibre positioning. In the SIGA process, the exact position of the V- grooves relative to the waveguide trenches is defined by the etch mask for the silicon master wafer.
The width of the V- grooves is determined by the KOH etching time. It is controlled precisely at various stages in the etching process by means of a microscope based piezo driven measurement system with a resolution better than 0. In order to specify the capability of our technology we have measured the position of dozens of fibres glued into V- grooves. As the experience has shown, a two-step process for the fabrication of passively fibre coupled waveguides is necessary.
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First, the waveguides are produced by filling the waveguide trenches with an IR-transparent monomer and by polymerizing it using UV curing. The waveguides are inspected with visible and IR light by clamping a fibre ribbon mechanically into the integrated plastic V-grooves. In a second step the fibre ribbon is fixed irreversibly in the V- grooves. By that way we have reached an insertion loss of 3. Most of the losses are attributed to waveguide imperfections.