Planar Waveguide Structure Research Articles

Scattering of an electromagnetic wave from a planar waveguide structure with a slightly 2D random surface

This paper deals with the scattering of an electromagnetic (EM) wave from a waveguide structure with a slightly rough surface. The waveguide structure is a dielectric film on a planar, perfectly conductive surface, and the top of the film is a two-dimensional (2D) homogeneous Gaussian random surface. The treatment is based on the stochastic functional theory where the random EM field is represented in terms of a Wiener - Hermite functional of the random surface. Numerical calculations show that enhanced backscattering and cross-polarization occur, but that no enhanced satellite peak appears for a 2D random surface, in contrast to the case of a 1D surface. The enhanced backscattering is caused by the interference of two double-scattering processes and is attributed to the existence of guided waves in the scattering structure.

Generalised approach to modelling shielded printed-circuit transmission lines

A new generalised approach for the full-wave analysis of shielded printed-circuit transmission lines with finite metallisation thickness is presented. A rigorous formulation for the electric field vector is employed, representing the hybrid electromagnetic field in layers of multidielectric media. The dyadic Green's function of the electric kind is derived as a kernel of the vector integral representations for the electric field. Based on the method of overlapping regions, the approach can be applied to the characterisation of a large class of planar waveguiding structures to yield a set of linear algebraic equations of the second kind with a compact matrix operator. Numerical examples are shown for single and coupled shielded planar transmission lines illustrating application of the method. The technique described allows obtaining accurate and mathematically correct solutions of planar waveguide eigenvalue problems.

Plastic lasers: Semiconducting polymers as a new class of solid-state laser materials

We demonstrate optically pumped lasing in submicron thick films, neat and undiluted, of photoluminescent conjugated polymers. Lasing is evidenced by a dramatic collapse of the emission line width (to as little as 7 nm) at very low pump energy thresholds (~10 μJ/cm 2). Laser action is found in over a dozen different conjugated polymers representing a variety of molecular structures, including poly( p-phenylenevinylene), poly( p-phenylene) and polyfluorene derivatives; lasing wavelengths in these materials span the visible spectrum. The short gain lengths in these conjugated polymers are attributed to the high density of chromophores, the large density of states associated with the interband (π-π *) transition in quasi-one-dimensional systems, and the Stokes shift which minimizes self-absorption and enhances stimulated emission in the absence of excited state absorption. The observation of lasing in this new class of solid-state laser materials is explained in terms of simple planar waveguiding structures which allow the distance traveled by emitted photons to readily exceed the short intrinsic gain lengths. The dependence of the threshold and the gain narrowed line width on the solvent from which the film is spin cast suggests that chain packing can be used to control lasing in some of these materials. The prospects for producing electrically pumped solid state polymer diode lasers using this class of materials are discussed in the context of the lowthreshold gain narrowing in submicron films.

Acousto-optic Bragg diffraction in SiGe/Si planar waveguides

The interaction of guided optical waves and surface acoustic waves (SAWs) in SiGe/Si planar waveguide structures is studied by first determining the electric field profile of the optical modes and the strain profiles induced by the propagating SAW. Coupled-mode theory provides the basis for the study of the acousto-optic interaction and results in the determination of diffraction efficiency as a function of acoustic frequency, for different material structures and acoustic powers. It is found that for most SiGe/Si structures significantly more acoustic power is needed to produce diffraction efficiencies comparable to those of material systems such as AlGaAs/GaAs. Also it is shown that a high germanium concentration could be desirable for increasing the diffraction efficiency to useful levels.

Refractive index and layer thickness of an adsorbing protein as reporters of monolayer formation

A method is presented for a separate real-time determination of refractive index and layer thickness of an adsorbing thin layer. The changing angular deflections of TE and TM modes in a dedicated planar waveguide structure are measured. A resolution of 0.01 in the refractive index and 0.5 nm in the average thickness is obtained. The method is illustrated with experimental results on the binding of an antibody to the substrate, both in a physisorption and in an immunoreaction. In the latter, results are consistent with an end-on binding of the antibody to the surface.

Impedance boundary method of moments for efficient analysis of lossy and leaky planar optical waveguide structures

An extension of the impedance boundary method of moments (IBMOM) which enables determination of the propagation characteristics of lossy and leaky planar dielectric waveguides is demonstrated. The use of extended impedance boundary conditions to facilitate the analysis of waveguiding structures with large stepwise changes in refractive index, such as ARROW structures, is discussed. Numerical results show excellent agreement between previously published data and those generated using the complex version of the IBMOM.

Reactive ion etching of sloped sidewalls for surface emitting structures using a shadow mask technique

A novel, very simple technique for the direct adjustment of the slope of facets in a reactive ion etching process is presented. The etching process is performed by screening the sample partially with an aluminum shadow mask, which is located inside the dark space of the plasma. The sidewall angle of etched lines, defined by a pattern mask on the sample, depends strongly on the distance between the shadow mask and the sample. The investigations are carried out with a methane-hydrogen plasma. The angle of inclination of the sidewalls can be varied in a controllable manner by more than 45°. This technique is well suited to fabricate 90° reflectors, which are necessary for three-dimensional optical interconnects with planar waveguide structures. To analyze the optical quality of the etched mirror plane, the beam transformation was investigated by reflectivity measurements using a single aluminum-evaporated mirror structure, which is illuminated by a focused laser beam at a wavelength of 633 nm.

Single-mode operation in symmetric planar waveguides using isotropic chiral media

We present the dispersion relations for symmetric planar waveguides in general isotropic media. The planar waveguide structure that utilizes chiral media in the cladding regions is emphasized. Unlike other symmetric planar waveguide configurations in isotropic media, this structure possesses a nondegenerate lowest-order mode. Therefore symmetric planar waveguides using chiral cladding materials can support single-mode operation.

Novel Polymeric Materials, Architectures, and Characterization Techniques for Electro-Optics

Abstract This contribution deals with recent developments in the field of integrated electro-optics. We first present a novel characterization technique based on optical waveguide microscopy that allows for the imaging of linear and nonlinear optical lateral heterogeneities in planar waveguide structures. Next, a new class of amorphous polymers is introduced: the charged groups of solid polyelectrolytes are compensated by counter-ions with a high χ(2) response. The advantage of these materials is their high level of doping that can be achieved without recrystallization observed for other host/ guest-systems. And finally, we present waveguide structures based on the Langmuir/ Blodgett/ Kuhn-technique with a complex internal optical architecture controlled at the molecular level.

Improvements of the two-dimensional FDTD method for the simulation of normal- and superconducting planar waveguides using time series analysis

Time-domain simulation results of two-dimensional (2-D) planar waveguide finite-difference time-domain (FDTD) analysis are normally analyzed using Fourier transform. The introduced method of time series analysis to extract propagation and attenuation constants reduces the desired computation time drastically. Additionally, a nonequidistant discretization together with an adequate excitation technique is used to reduce the number of spatial grid points. Therefore, it is possible to simulate normal- and superconducting planar waveguide structures with very thin conductors and small dimensions, as they are used in MMIC technology. The simulation results are compared with measurements and show good agreement.

Si-based nanostructure waveguides

We investigate the possibility of constructing nanostructure waveguides using Si-based materials. For this purpose we evaluate the dielectric function of strain-symmetrized (Si)10−n/(Ge)n strained-layer superlattices (SLS’s) with n=3, 5 and 7, and (Si)6/(Ge)4 SLS coherently grown on a Si(001) surface, as well as that for bulk Si1−n/10 Gen/10 alloys with n=3, 5 and 7, and bulk Si. In particular we explore the possibility of constructing waveguides using the materials (Si)6/(Ge)4 SLS, coherently grown on a Si(001) surface, and bulk Si. We investigate the case of planar waveguide structure, giving results concerning the propagation and penetration of the transverse magnetic modes.

Enhanced scattering from a planar waveguide structure with a slightly rough boundary.

The scattering problem of an incident wave from a waveguide structure with a slightly rough surface is studied. The waveguide structure is considered to be a dielectric film deposited on a planar, perfectly conducting metal surface, and the top surface of the film is assumed to be a randomly rough surface. The stochastic scattered wave fields are represented in terms of orthogonal functionals with the Wiener coefficients. These coefficients are determined by applying the approximated boundary conditions expanded up to the third order of the random surface function. The analytical expressions for the coefficients of the first three terms are obtained rigorously up to the second order of the surface roughness so as to satisfy the reciprocity. It can be easily shown that our results are the same as those obtained by perturbation theory if we expand them in powers of the surface roughness. However, we have the so-called mass operator in the denominator of the coefficients, which can be used to determine the perturbed propagation constants of the guided waves in the presence of a rough surface and remove the divergence difficulty in the common perturbation theory. The numerical calculations show that there are some well-pronounced satellite peaks in the incoherent scattering distribution, in addition to the enhanced backscattering peak, when the waveguide structure can support two or more than two guided modes. This is caused by the interference of two double-scattering processes and is attributed to the existence of the guided waves in the scattering structure.

Spontaneous emission coupling to radiation and guided modes of planar waveguide structures

A general analysis of spontaneous emission in the vicinity of a symmetric slab dielectric waveguide is presented using explicit energy-normalized functions for the complete set of bound and radiating TE and TM modes. Expressions for the spontaneous emission rates are derived for each mode type, and calculated results are presented illustrating the emission behavior as a function of the position of the radiating atom, for various slab waveguides. The model is used to analyze the spontaneous emission coupling efficiency to guided modes in planar erbium-doped amplifier structures. Spontaneous emission factors for the TE and TM modes are calculated for the cases of erbium doping of the core and of the cladding. >

Exact and variational Fourier transform methods for analysis of multilayered planar waveguides

Exact and variational Fourier transform methods for the analysis of generalised planar waveguide structures are described in detail. Results are presented for specific structures of technological importance, namely the rib and channel waveguides and the rib waveguide directional coupler. These results establish the accuracy of Fourier transform methods in calculating critical design parameters such as propagation constant, field profile and coupling length. Moreover, they compare very favourably with purely numerical techniques in terms of speed and required computer resources.

A stretched coordinate technique for numerical absorption of evanescent and propagating waves in planar waveguiding structures

Berenger's PML technique is modified to allow for the absorption of evanescent and propagating waves in FDTD modeling of wave propagation in planar waveguiding structures. Analytic results illustrate the validity and capability of the proposed modification. Numerical studies explain the numerical implementation of the modified PML in the FDTD and in the compact 2D-FDTD algorithms. Guidelines for the proper selection of the various parameters that govern the performance of the modified PML are presented. The results from simulations indicate that the proposed modified PML grid truncation can be used efficiently for highly accurate numerical analysis of planar waveguiding structures.

Fabrication of Er Doped Glass Films as Used in Planar Optical Waveguides

AbstractSilica integrated optical circuits are expanding in functionality to include optically active waveguides. Traditionally, the planar optical waveguide structures include silica based glass films such as thermal oxides, phosphorous, and boron-phosphorous doped glasses. Various efforts have successfully doped conventional waveguides with Er, typically by solution doping. Material issues such as rare earth solubility and glass structure dictate that efficient optical amplifiers based on such waveguides have path lengths in excess of 10–15 cm. We have developed an alternative strategy using Er-doped soda-lime silicate glass films on silicon. The waveguide processing utilizes methods of deposition similar to those used in silicon IC technology, with modificatons in the compositions and thicknesses. In these glasses the effective solubility limits are relaxed and we have successfully fabricated short path length devices which demonstrate net gain of more than 4 dB/cm. Short path length devices offer a potential advantage in highly integrated multi-channel devices and offer an additional building block in system architectures.

Plasma Synthesis of Rare Earth Doped Integrated Optical Waveguides

AbstractWe describe a novel means for the production of optically active planar waveguides. The technique makes use of a low energy plasma deposition. Cathodic-arc-produced metal plasmas are used for the metallic components of the films and gases are added to form compound films. Here we discuss the synthesis of A12-xErxO3 thin films. The erbium concentration (x) can vary from 0 to 100% and the thickness of the film can be from Angstroms to microns. In such material, at high active center concentration (x=l% to 20%), erbium ions give rise to room temperature 1.53μm emission which has minimum loss in silica-based optical fibers. With this technique, multilayer integrated planar waveguide structures can be grown, such as Al2O3/Al2-xErO3/A12O3/Si, for example.

Defects and Their Origin in Thin Films of (001) Alkaline Earth Oxides

AbstractMgO is used as an optical isolation layer for waveguides epitaxially grown on silicon. The crystalline perfection of MgO is a critical issue because it serves as a substrate for the single crystal, perovskite guiding layer. Imperfections in the MgO will result in imperfections in the guiding layer and lead to large optical losses for the planar waveguide structure. We show that the most common defect to form in thin films of MgO are twin boundaries between {111}-type planes. The highest density of twins is observed when (001) MgO is grown directly on silicon/MgO interlayers containing barium. Twinning is shown to accommodate the large size of barium impurities incorporated in the MgO films through the formation of internal grain boundaries and open surfaces other than the growing (001) of MgO.

Antiresonant waveguide add/drop filter using Fabry-Pérot interference

We describe planar waveguide structures that accomplish the Fabry-Pérot filtering functionality by using the wavelength selective coupling between antiresonant optical waveguides. By using different cladding layer thicknesses wavelength selectivity is achieved despite the fact that the coupled waveguides have equal core thicknesses, in contrast with filters based on conventional waveguides. For the polymer-based configuration investigated here a resolution of 1.2 nm was obtained with a free spectral range of 12 nm. We also describe a dual output filter which could drop or add two different wavelengths at once in a wavelength division multiplexing (WDM) system.

Method of lines for the analysis of optical waveguidestructures with complex refractive indices usinga pole-free eigenvalue determination

The method of lines can be efficiently used for the numerical modelling of planar waveguide structures with complex refractive indices in integrated optics, employing singular value decomposition. This is demonstrated for the example of an asymmetric active rectangular waveguide coupler.