Showing papers on "Guided wave testing published in 1999"

Determination of guided and leaky modes in lossless and lossy planar multilayer optical waveguides: reflection pole method and wavevector density method

Abstract: Two numerical methods, the reflection pole method (RPM) and the wavevector density method (WDM), are introduced for determining the propagation constants of guided and leaky modes in lossless and lossy planar multilayer waveguides. These methods are based on the extraction of propagation constants from Lorentzian-type peaks of the reflection coefficient (RPM) or on the density of wavevectors of the structure (WDM). Furthermore, in the case of the RPM the propagation constants can be determined with the help of the phase variation of the denominator of the reflection coefficient in conjunction with an optimization procedure. Both methods are tested on numerically "challenging" multilayer waveguides such as a two-metal-layer waveguide, a multilayer lossy waveguide, and an ARROW waveguide. The results produced by both methods are in good agreement with other numerical techniques but are obtained without the need for solving a dispersion equation in the complex plane. In addition, an approximate but easily implementable method is proposed which verifies whether a cluster of radiation modes can be accurately represented by a single leaky mode.

Polymer electro-optic devices for integrated optics

Abstract: Recent advances in polymer electro-optic polymers and in fabrication techniques have made possible advances in polymer optical guided wave devices which bring them much closer to system ready. The processing of a new thermal set FTC polymer and its incorporation into a high-frequency, low-Vπ optical amplitude modulator are reviewed. The design and fabrication of 100 GHz modulators and their integration with rectangular metal waveguides using an anti-podal finline transition with a flexible Mylar substrate is discussed. High-speed polymer modulators with balanced outputs and the in situ trimming of the output coupler is described. More complex guided wave devices using polymers are demonstrated by the photonic rf phase shifter. Techniques for integrating both passive and active polymers into the same optical circuit without the need for mode matching is presented and demonstrated. To reduce the Vπ of a polymer amplitude modulator to 1 V or under, a technique of constant-bias voltage is demonstrated. Finally, a technique to directly laser write electro-optic polymer devices is reviewed.

Lamb wave generation and reception with time-delay periodic linear arrays: a BEM simulation and experimental study

Abstract: A time-delay periodic linear array model has been proposed for Lamb wave generation and reception in plates. The unilateral guided wave emitting and receiving have been achieved by applying the interference principle in the array designs. A hybrid BEM technique has been developed and applied to simulate the wave generation procedure with such arrays and to analyze the performance. Experimental results also are presented for two typical time-delay periodic arrays to qualitatively validate the theoretical designs. The effects of the array parameters on the array performance, such as the selectivity of Lamb modes and effectiveness of Lamb wave generation, are investigated through the 2-D phase velocity-frequency spectrum analyses as well as Lamb mode wave structure calculations.

Diffraction efficiency and guided light control by two-dimensional photonic-bandgap lattices

Abstract: We report on the measurement of the diffraction efficiency of two-dimensional photonic-bandgap lattices consisting of a triangular array of circular air holes etched in a semiconductor waveguide. We use the spontaneous emission of the material as an internal point source. Combined with previous reflectivity and transmission measurements, the diffraction data allow us to assess the total amount of out-of-plane losses experienced by a guided wave traversing the dielectric lattice, as a function of the lattice pitch. We found that these losses are particularly weak for some range of parameters, especially in the photonic bandgap of interest. We discuss the reasons why they can be substantial with other parameters.

A guided-wave optical electric field sensor with improved temperature stability

Abstract: This paper reports on the study of an electric field sensor based on the Y-cut LiNbO/sub 3/ waveguide which has slight temperature dependence. The errors in the electric field measurements due to temperature variations were theoretically studied and the increase in the error with a temperature change of 100 K has been proven to be extremely low, 2.5%. As a technology to achieve high temperature stability, we adopted a new method of attaching optical fibers to a waveguide and a method of suppressing the pyroelectric effect by depositing (ITO) In/sub 2/O/sub 3/-SnO/sub 3/ films onto the Z-faces. The temperature dependence of the fabricated sensor was measured and it was found that the measurement errors in a broad temperature range from -30 to 90/spl deg/C was /spl plusmn/7% or less.

Multimode guided wave inspection of piping using comb transducers

Abstract: This study investigates the detection of discontinuities in piping using a multimode technique. The potential benefits of guided wave inspection technique for piping inspection have been well documented. A multimode approach was executed via a linear array comb transducer. A linear array comb transducer was used to generate multiple modes. Detection of discontinuities in 101.6 mm (4 in.) carbon steel insulated piping using the comb transducer was performed on a demonstration piping system.

Resonance modes and losses in 1-3 piezocomposites for ultrasonic transducer applications

Abstract: The article presents the results of a recent investigation on the ultrasonic performance of 1-3 piezocomposites. Using a guided wave approach, the electromechanical properties of the thickness resonance are modeled and the results are compared with the experimental data. The influence of various losses in a 1-3 composite on the dispersion curves and the quality factor for the thickness mode is examined. It is found that the reduction in the quality factor of a composite compared with piezoceramic is mainly due to the acoustic coupling between the two constituents. Even for a composite with the mechanical Q of the polymer higher than that of the ceramic, the mechanical Q of the composite is still lower than that of the ceramic except when the ceramic volume content is very low. Hence, in most of piezoceramic polymer composites, the mechanical Q of the ceramic phase plays a major role in determining the quality factor of a 1-3 composite transducer. For the lateral modes in a 1-3 composite, it is found experimentally that the frequencies of the two lowest lateral modes can be determined approximately by the shear wave velocity and the width of the polymer gap over a broad ceramic volume fraction range, suggesting that they correspond to the half-wave standing waves in the polymer gap.

Generation and reception of ultrasonic guided waves in composite plates using conformable piezoelectric transmitters and optical-fiber detectors

Abstract: A condition monitoring nondestructive evaluation (NDE) system, combining the generation of ultrasonic Lamb waves in thin composite plates and their subsequent detection using an embedded optical fiber system is described. The acoustic source is of low profile with respect to the composite plate thickness, surface conformable, and able to efficiently launch a known Lamb wave mode, at operating frequencies between 100 and 500 kHz, over typical propagation distances of 100 to 500 mm. It incorporates both piezocomposite technology and interdigital design techniques to generate the fundamental symmetrical Lamb wave mode in both metallic and carbon-fiber composite plates. Linear systems and finite element modeling techniques have been used to evaluate the operation of the transducer structure, and this is supplemented by experimental verification of the simulated data. An optical fiber, either bonded to the surface or embedded across the length of the composite plate samples, is used to detect the propagating ultrasonic Lamb waves. Single mode silica fiber has been used in conjunction with a portable 633 nm Mach-Zehnder interferometer for signal demodulation and subsequent data acquisition. This hybrid system is shown to generate and detect the fundamental symmetrical Lamb wave (s/sub 0/) in both carbon-fiber and glass-fiber reinforced composite plates. Importantly, the system signal-to-noise ratio (SNR) associated with the acoustic source compares favorably with s/sub 0/ Lamb wave generation using a conventional transducer and angled perspex wedge arrangement.

Guided-wave acoustooptic interaction with phase modulation in a ZnO thin-film transducer on an Si-based integrated Mach-Zehnder interferometer

Abstract: This paper presents the design and the realization of a novel integrated Mach-Zehnder interferometer (MZI) with heterodyne scheme. Well-controlled machining as well as ZnO thin-film transducer integration on the same Si substrate permits to transform an optically passive device to an active device with sinusoidal phase modulation. Theoretical and experimental results are presented, demonstrating that an efficient sensor can be designed and fabricated.

Stress analysis method for elastically anisotropic material based optical waveguides and its application to strain-induced optical waveguides

Abstract: A numerical approach for the stress analysis of elastically anisotropic material-based optical waveguides is newly formulated with the finite element method (FEM). The stress analysis method developed here is linked to the guided mode analysis method to produce a two-step analysis of acoustooptic modulation of optical waveguides. Numerical examples are shown for strain-induced optical waveguides on LiNbO/sub 3/ substrates.

Incoupling waveguide holograms for simultaneous focusing into multiple arbitrary positions.

Abstract: A design method is presented that enables the realization of a novel type of incoupling waveguide hologram (IWGH) that simultaneously focuses the incoupled light to any desired positions in the waveguide. IWGH's, or grating couplers, are gratinglike structures etched into the waveguide surface. They couple the light incident from free space into the waveguide. The grating lines can be dislocated with respect to each other to provide phase modulation of the incoupled light. By use of this phase modulation, novel beam splitting and focusing functions can be built into the IWGH's. The new design algorithm is based on a model that assumes a simple relation between the incident light wave and the locally excited guided wave. This model is used to obtain an efficient formulation of the optimization problem. Four different IWGH's were designed and fabricated in InP for light at 1550-nm wavelength. Experiments confirm that these IWGH's are capable of incoupling the incident wave and simultaneously splitting and focusing the guided wave into multiple positions in the waveguide at different distances from the IWGH.

Effects of layered sediments on the guided wave in crosswell radar data

Abstract: To understand how layered sediments affect the guided wave in crosswell radar data, traces are calculated for a model representing a sand layer between two clay layers. A guided wave propagates if the wavelengths in the sand layer are similar to the thickness of the sand layer. The amplitude of the guided wave but not its initial traveltime is affected by the thickness of the sand layer. In contrast, both the amplitude and the initial traveltime are affected by the locations of the transmitting and receiving antennas, the electrical conductivity of the sand layer, and the dielectric permittivity of the sand layer. This permittivity can be estimated from the initial traveltime. The effects of the layering on the waves in these calculated traces also are observed in field traces, which were collected in layered sediments.

Half-leaky guided wave determination of azimuthal anchoring energy and twist elastic constant of a homogeneously aligned nematic liquid crystal

Abstract: Optical excitation of half-leaky guided modes has been used to explore the director distortion of a homogeneously aligned nematic liquid crystal (BDH E7) under application of an in-plane electric field. Homogeneous alignment is realized by obliquely evaporated SiOx layers with an in-plane field being applied across a 3 mm gap between gold electrodes. The director is initially aligned approximately parallel to the edges of the electrode gap. By modeling the director profile in the cell to fit the half-leaky guided mode reflectivity data, both with and without applied fields, and then comparing the field induced distortions to continuum theory, we obtain both the twist elastic constant k22 and the surface azimuthal anchoring coefficient, Wa. At 23.7 °C we find that k22=6.5×10−12 N and Wa=2.3×10−6 Jm−2.

Fabrication and characteristics of three-dimensionally buried porous silicon optical waveguides

Abstract: A fabrication technology of three-dimensionally buried porous silicon (PS) optical waveguide with an extremely high refractive index contrast is presented, including its fundamental properties. The origins of attenuation losses are investigated by experimental and theoretical analyses in terms of microscopic observations, edge emission measurements, polarization mode determination of guided wave, and evaluation of bending loss. The results of these studies indicate that attenuation losses in PS waveguides are due to self-absorption by residual silicon, structural and optical inhomogeneities in the core region, and roughness at interfaces between the core and the cladding layers. Some possible ways for reducing these attenuation losses are discussed. It is also demonstrated that a buried bent PS waveguide with an extremely small curvature of 250 μm can be fabricated by simple planar processing, and that a visible optical wave propagates along it owing to a significantly high refractive index contrast betwe...

Guided-wave phase-matching of ultrashort-pulse light

Abstract: We review the use of hollow waveguides for frequency conversion of ultrafast laser pulses the ultraviolet and extreme ultraviolet. Phase-matching of these processes is reached through a balance of gas and waveguide dispersion. By mixing 400 nm with 800 nm light, ultrashort (8 fs) pulses are generated near 270 nm with high efficiency > 20%. Tuning of the longer-wavelength component in the mixing process allows tuning of the output from 215–308 nm. In the XUV, this guided-wave phase-matching has allowed an increase of conversion efficiency of high-order harmonic generation of 100–1000x over that obtained with a gas jet, in an experimentally-convenient geometry.

Efficient method-of-moments formulation for the modeling of planar conductive layers in a shielded guided-wave structure

Abstract: An electric-field integral-equation formulation discretized via the method of moments (MoM) is proposed for the analysis of arbitrarily shaped planar conductive layers in a shielded guided-wave structure. The method results in a generalized scattering matrix (GSM) for the planar structure and can be used with other GSM's, derived using this or other techniques, to model cascaded structures in waveguide. The Kummer transformation is applied to accelerate slowly converging double series expansions of impedance matrix elements obtained in the MoM solution. In this transformation, the quasi-static part associated with a singularity of the electric-type Green's function in the region of a conductive layer is extracted and evaluated in terms of modified Bessel functions, resulting in a dramatic reduction of terms in a double series summation. The proposed technique permits the modeling of a variety of conductive frequency-selective surfaces, including quasi-optical grids and patch arrays for application to spatial power combining.

Theory of Antenna Radiation from Photonic Band-Gap Materials

Abstract: A unified formulation of antenna radiation from photonic band-gap (PBG) materials is described in this paper. An analytical array scanning method is applied to formulate the boundary-value problem associated with source interaction with infinite periodic structures. A double vector-integral equation formulation in conjunction with multi-stage moment methods is introduced to characterize the current distribution over antenna elements, the near fields, and associated circuit parameters of interest. Asymptotic method is used to find the far-zone radiated waves and the periodic guided waves, which are used subsequently to determine the antenna radiation characteristics including gain (directivity) patterns, efficiency, and periodic guided wave power pattern. Of particular interest is the photonic band-gap effect to the periodic guided waves. Potential high-gain surface wave antenna using a PBG substrate is also discussed.

Apparatus and method for inspection of pipes and tubes using guided wave probe

Abstract: An apparatus and method for directing ultrasonic and magnetostrictively generated mechanical waves from an exterior point to an interior point within a small diameter tube, pipe, or cylindrical structure. The present invention incorporates an external mechanism for generating waves in a cylindrical waveguide tube gun (10) of a size small enough for insertion into the target tube (24) and configured so as to maintain mechanical contact with an inside diameter of the target tube (24). Standard ultrasonic wave generating devices or magnetostrictive/mechanical wave generating coils (16, 18, 20) are positioned on the waveguide (12) external to the target tube (24) and generate appropriate mechanical waves through the waveguide (12) to a point interior to the target tube (24). A mechanical interface (14) between the waveguide (12) and the inside diameter surface of the tube is positioned and provided at a point within the target tube (24) to transfer both the interrogating waves (36) and the received return signal waves (37) between the target tube (24) and the waveguide (12).

Long Range Lamb Wave Inspection: the Effect of Dispersion and Modal Selectivity

Abstract: Guided acoustic waves, such as Lamb waves, are highly attractive for the rapid inspection of plate and pipe-like [1–3] structures. However, guided wave inspection is more complicated than conventional bulk wave ultrasonic inspection, for two reasons in particular: the existence of multiple modes of wave propagation, and the generally dispersive nature of these modes [4]. In most successful applications of guided waves for long range testing, the bandwidth of the acoustic energy supplied to the system is constrained by using a signal such as a Hanning or Gaussian windowed toneburst. In conjunction with the transducer design, the use of limited bandwidth input signals can be used to suppress unwanted modes and limit dispersion in the desired mode [4].

Two-dimensional 45/spl deg/ surface-normal microcoupler array for guided-wave optical clock distribution

Abstract: Surface-normal couplers are indispensable parts of a guided-wave optoelectronic interconnects for the coupling of optical signals into and out of the waveguides while facilitating the packaging. In this paper, integration of the 45/spl deg/ surface-normal couplers at each fanout end of the H-tree waveguide structure is described. An optical clock signal distribution system is under development using polyimide based H-tree waveguide structure. The coupler is a 45/spl deg/ slanted end surface of the polyimide waveguide. The coupler works for a wide range of wavelength. The experimentally estimated output coupling efficiency is nearly 100%. To determine the optimized size and shape of the photodetector, near and far field diffraction patterns are evaluated. Experimental results conclude that the phenomenon is dominated by the fundamental mode of the highly multimode waveguide.

Path-reversed substrate- guided-wave optical interconnects for wavelength-division demultiplexing.

Abstract: A path-reversed substrate-guided-wave holographic interconnection scheme is investigated for a wavelength-division demultiplexing application. Using a beveled edge of a waveguiding plate allows optical signals to be coupled into the waveguiding plate and then to be coupled out of the plate by a waveguide hologram. Theoretical analyses are given for dispersion, bandwidth, and recording parameters of various guided-wave holographic gratings. A device is fabricated with a 45° incident angle and a 45° diffraction angle by use of a 20-µm photopolymer film. The 3-dB bandwidth of the device is measured to be 20 nm. Four-channel wavelength demultiplexing is demonstrated at 796, 798, 800, and 802 nm with no cross talk observed. A one-to-five cascaded four-channel wavelength-division demultiplexer with ±5% energy uniformity under s polarization is also demonstrated to increase the user-sharing capacity. Twenty fan-out channels (5 × 4) are achieved experimentally.

Asymmetric modes on symmetric nonlinear optical waveguides

Abstract: We study a symmetric nonlinear value problem in all R, arising in nonlinear optics from the study of propagation of electromagnetic guided waves through a layered medium with a nonlinear response. By variational arguments, we prove the existence of a positive asymmetric solution of the problem, corresponding to an asymmetric guided wave.

Performances of optical multi-chip-module interconnects: comparing guided-wave and free-space pathways

Abstract: We simulate and compare optical transmission efficiencies, throughputs and interconnection lengths of free-space and POF-based guided-wave multi-chip-module optical interconnection demonstrators for different types of microcavity emitters.

Ka Band Quasi Optical Test Bench using Focusing Horns

Abstract: This paper presents a measurement set up developed for millimeter wave characterization of passive or active quasi optical components such as filters, polarizers, amplifiers or multipliers. The main quasi optical elements of this bench are the focusing horns which allow guided wave coupling to the quasi optical components. These horns are designed using the Gaussian beam theory and FDTD software on a personal computer. The quasi optical measurements are performed according to a TRL calibration method in the Ka band for passive circuit characterization such as a dielectric slab. These measurements give the scattering matrix of quasi optical components which can be used for simulation in classical CAD software.

Applications of Guided Wave Techniques in the Petrochemical Industry

Abstract: Guided wave techniques have gained growing attention in the petrochemical industry because of their two primary advantages: ability to examine areas that cannot be reached by other NDE techniques and ability to cover large surface areas cost-effectively. For the former, guided wave techniques are required to perform both defect detection and defect sizing. An example of such applications is use of a Lamb wave technique to detect and quantify piping wall loss due to localized corrosion at pipe supports in lieu of pipe lifting and conventional inspections [1,2]. For the latter, guided wave techniques are primarily needed for their detection capability to perform global and/or on-steam inspections. Examples include a Lamb wave technique for rapid inspections of pipes, heater tubes, and thin-walled vessels for localized corrosion, and cylindrically guided wave techniques for long range piping inspection [3,4]. In addition to these current techniques/applications, new guided wave techniques are being developed to inspect heat- exchanger tubing [5], buried piping at road crossings or underneath dikes [6,7], and offshore risers under coating/concrete protection [7]. These current applications are reviewed and potential applications are discussed in this paper. Particular attention is given to the piping support inspection as an example to show how guided wave techniques can be used to quantify corrosion wall loss.

Ultrasonic Waves and Material and Defect Characterization in Composite Plates

Abstract: Analysis of wave propagation and scattering in a composite plate is complicated by the anisotropic properties of the laminae. An accurate computation of the wave field excited by transient sources in such a plate is required in order to characterize the anisotropic stiffness properties of the laminae and for ultrasonic evaluation of delamination defects. Here, a variational formulation has been used for deriving the dispersion equation governing guided elastic waves in laminated plates. The equation is a matrix eigenvalue problem that can be solved for the wavenumbers at given frequencies or for the frequencies at given wavenumbers. For accurate evaluation of the eigenvalues it is necessary to have a large number of sublayers, which results in large matrices and is not computationally efficient. However, the matrix formulation combined with analytical refinement is shown to give fairly accurate results that agree well with experiments. In this article, results for guided wave dispersion and the inverse pr...

Optical modeling of waveguide photonic nanostructures using the radiation spectrum method (RSM) with evanescent modes

Abstract: In this work, we study the effects of the evanescent modes in the simulation and modeling of optical integrated circuits based on photonic bandgap structures. We show that the contribution of these modes in the energy transfer in structures like the MOEM structures, can not be neglected. The radiation spectrum method, recently developed by the authors for the guided wave devices, is thus extended to account for the evanescent mode propagation. Applying this technique on an air-gap in a suspended waveguide a model of this gap is developed in terms of its parameters. This model is then integrated in an all optical simulator to predict the performance of photonic structures. Such technique enables to design and to optimize the photonic integrated circuits taking the evanescent modes effects into account.

Efficient and accurate numerical analysis of multilayer planar optical waveguides

Abstract: This paper presents a numerical method for computing the propagation constant of electromagnetic modes supported for multilayer planar optical waveguides. We report a method for solving the dispersion equation for a guided wave structure of interest in the complex plane via Chauchy's integration. The method is applicable to lossless, lossy and ARROW waveguide structures and can handle both leaky and guided modes. Contrary to the methods currently published in the literature, which are based on a numerical derivative of the dispersion equation, we propose an analytical derivative for the latter. This has a double impact: improved accuracy and reduced CPU time. The specific integration contour for leaky modes will be discussed. The results are in excellent agreement with several results published in the literature.