Showing papers on "Guided wave testing published in 1988"

Silica-based single-mode waveguides on silicon and their application to guided-wave optical interferometers

Abstract: Low-loss silica-based single-mode waveguides and directional couplers are fabricated on silicon substrates. Their application to Mach-Zehnder interferometer type guided-wave devices is demonstrated. Optical switches or tunable optical couplers are fabricated using the thermooptic effect. Asymmetrical Mach-Zehnder interferometers are successfully applied to multi/demultiplexers for optical FDM transmission systems. >

Propagation and optical interaction of guided acoustic waves in two-mode optical fibers

Abstract: Acoustic modes propagating in cylindrical solid rods are considered. A review of the properties of several mode groups is given, and computed results are shown for a wide range of material properties. The lower mode of each group is relevant for an all-fiber-optic frequency shifter recently demonstrated. For these modes, dispersion relations, mode patterns, power relations, and acoustooptic coupling strength are calculated. Some experimental results are compared with the calculations, and alterations to improve the frequency shifter are proposed. >

Propagation of guided waves in fluid-coupled plates of fiber-reinforced composite

Abstract: Guided wave propagation in fluid‐coupled plates of fiber‐reinforced composites has been investigated by studying ultrasonic reflection in these structures. From measurements of ultrasonic reflection on unidirectional graphite‐epoxy plates over a range of incident angles, experimental dispersion curves using a total‐transmission criterion for leaky plate waves have been constructed. Theoretical calculations with no adjustable parameters demonstrate excellent agreement with the experimental data. Unusual behavior observed in the fundamental total‐transmission curve led to a reexamination of the mode identification criteria. Both the total‐transmission curves and the normal modes of the fluid‐coupled plate differ significantly from the result expected on the basis of the widely used Cremer coincidence condition to identify propagating plate waves. It is found that these differences are particularly pronounced in cases where the ratio of fluid to solid densities is high, as for composite materials. The existence of such behavior is also demonstrated numerically in a fluid‐coupled aluminum plate by arbitrarily increasing the density of the fluid.

Identification of longitudinal acoustic modes guided in the core region of a single-mode optical fiber by Brillouin gain spectra measurements.

Abstract: Several resonance peaks owing to an interaction between light-wave and guided modes of longitudinal acoustic waves are observed in the Brillouin gain spectra for a single-mode fiber with a GeO2-doped core and pure silica cladding. Brillouin gain spectra measurements are carried out at 1286- and 1550-nm wavelengths. Longitudinal acoustic modes guided in the GeO2-doped core region are identified by applying the analysis of leaky modes in a fiber acoustic waveguide.

Fiber attachment for guided wave devices

Abstract: Reviews the status of fiber attachment to guided wave devices. Current methods for achieving low fiber-waveguide-fiber insertion loss are discussed and techniques for aligning and permanently attaching fibers are described. >

Method and apparatus for selecting detection of changes in samples by integrated optical interference

Abstract: In an integrated optical interference method, polarized laser light is incoupled into a planar waveguide, propagates in the waveguide as a guided wave, which consists of two mutually coherent, orthogonally polarized modes, interacts at least once with the sample, which is applied to the surface of a section of the waveguide called measuring section, and subsequently is outcoupled out of the waveguide. The time dependent phase difference ΔΦ(t) between the two orthogonal polarization components of the outcoupled light is measured with a device comprising photodetectors and polarization optical components.

Integrated-optic wavelength multiplexers on lithium niobate based on two-mode interference

Abstract: The principle of the wavelength-dependent two-mode interference (TMI) in guided wave devices is utilized to build up integrated-optic dual-channel wavelength-division multi-/demultiplexers (WDM) for single-mode systems. The device characteristics are analyzed by analytical and numerical methods where special emphasis is given to the wavelength dependence of the channel spacing. These devices are fabricated by titanium indiffusion into X-cut and Y- and Z-propagating LiNbO/sub 3/, where the Z-propagating configuration is preferred for polarization independent operation. In the wavelength range between 1.3 and 1.6 mu m, insertion losses (fiber-waveguide-fiber) below 3 dB, channel spacings of 30-40 nm, and far-end crosstalk values of 26-40 dB are achieved. The measured low temperature sensitivity of the wavelength shift of 5.6*10/sup -2/ nm/ degrees C and the possibility of electrooptic tuning at a rate of 2.5 nm/V allow the realization of high performance devices at reduced fabrication tolerances. >

Nonlinear codirectional guided wave mode conversion in grating structures

Abstract: The authors discuss the operational characteristics of a new all-optical device, based on a nonlinear grating, potentially capable of all-optical switching between dissimilar waveguide modes. The use of a grating allows for a substantial reduction in switching-power requirements, still permitting complete power-dependent mode-conversion. An unexpected feature is that efficient switching requires detuning from the low-power wave vector matching condition. The switching behavior is very sensitive to wavelength detuning, both from the Bragg condition and from the higher-order mode cutoff condition. Furthermore, operation of the device is strongly nonreciprocal with respect to interchanging the mode launching condition. >

Orientationally Ordered Electro-Optic Materials

Abstract: Suitable materials for processing optical information are critical for implementation of all-optical and electro-optical communications and data processing systems. These technologies require materials with large optical nonlinearities, which certain organic materials have been shown to possess.[1] [2] [3] [4] Guided wave electro-optic systems require not only large optical nonlinearities, but also materials suitable for waveguiding and integration. Material considerations include manufacturability, that is capability of fabrication into reproducible devices; and integrability with sources, electronics, detectors, and interconnects. Additionally, materials should possess favorable dielectric properties: a low dielectric constant and dielectric loss, and the requisite optical quality for producing low-loss optical waveguides.

Demonstration of all‐optical modulation in a vertical guided‐wave nonlinear coupler

Abstract: The performance characteristics of an AlGaAs dual waveguide vertical coupler with a nonlinear GaAs/AlGaAs multiquantum well coupling medium are demonstrated. The structure was grown by molecular beam epitaxy and fabricated by optical lithography and ion milling. The nonlinear coupling and modulation behavior is identical to that predicted theoretically. The nonlinear index of refraction and critical input power are estimated to be n2=1.67×10−5 cm2/W and Pc=170 W/cm2, respectively. This device also allows reliable measurement of the nonlinear refractive index for varying quantum well and optical excitation parameters.

Nonlinear waves in saturable self-focusing thin films bounded by linear media

Abstract: 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 TE/sub 0/ 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. >

Demonstration of guided-wave phenomena at extreme-ultraviolet and soft-x-ray wavelengths

Abstract: We report an explicit demonstration of classical guided-wave propagation at XUV and soft-x-ray wavelengths. Experiments were performed using narrow-band synchrotron radiation at 5, 20.8, 21, and 30 nm. Free-standing gold transmission gratings served as waveguide structures. These structures had a 300-nm grating period with waveguide channel widths as small as 100 nm and were as thick as 700 nm in the direction of guided-wave transmission. Guided-wave phenomena were manifest in strongly asymmetric diffraction patterns resulting from the angular tilt of the transmission-grating normal from the incident-beam direction.

Optical waveguide element, method of making the same and optical coupler employing optical waveguide element

Abstract: An optical waveguide element includes an optical waveguide formed on a light-transmissive dielectric substrate and having a higher refractive index than the refraction index of the substrate, the optical waveguide including a region having an effective refractive index which varies nonlinearly in a direction in which a light wave is propagated through the optical waveguide. The light wave guided through the optical waveguide enters the region, in which the angles of incidence and reflection of the guided wave at the boundary between the region and the substrate is gradually reduced due to the variation in the effective refractive index. When the angles of incidence and reflection of the guided wave becomes smaller than a critical angle, the guided wave is emitted out of the waveguide. Since the effective refractive index changes nonlinearly with respect to the distance the guided wave is propagated, the light emitted into the substrate tends to converge at a point, and the beam pattern of the emitted light is spread less.

Integrated optical interference method

Abstract: In an integrated optical interference method, polarized laser light (3e) is input into a planar waveguide (1/2) in which it is propagated as a guided wave (3) consisting of two mutually coherent orthogonally polarized modes. The light interacts at least once with the test sample (4) placed on the surface of a section of the waveguide (1/2; 1a/2) termed a measuring position (1'). It is then output from the waveguide (1/2) and the time-dependent phase difference DELTAPHI(t) between the two mutually orthogonal polarization components in the output light (3a) is measured by means of a device (10) consisting of photodetectors and polarizing optical components.

Analysis of anomalous resonance effects in multilayer-overcoated, low-efficiency gratings

Abstract: A Rayleigh–Fourier method is used in an analysis of anomalous resonance effects on multilayer-overcoated, low-efficiency gratings. The ratio of grating amplitude to wavelength, H/λ, is 0.016. For wavelength-to-grating-period values such that only the specular beam and the −1 diffracted order are reflected from the grating, such H/λ values yield a nominal −1-order efficiency on the order of 2%. However, for carefully selected parameters such that coupling of incident beam energy into guided waves is achieved, the −1-order efficiency may exceed 50% and is accompanied by a corresponding reduction in the specular beam intensity. The range over which this anomalous behavior occurs is quite narrow. Composite dielectric structures of one to ten layers are considered.

Guided and surface electron drift waves in plasmas.

Abstract: The existence of guided and surface electron drift waves in magnetoactive plasmas is demonstrated. The conditions for each of these modes to exist are found It is shown that the surface mode is unstable if the gradients of the plasma density and of the externally applied dc magnetic field are parallel within a localized region of the plasma.

Transfer matrix theory of leaky guided waves

Abstract: We present a general transfer matrix approach for the propagation of guided waves in presence of inhomogeneities or «scatterers». We particularly address the problem of the coupling with radiation modes leading to a leakage of the guided wave to the surrounding bulk medium at each scattering. Examples are surface acoustic waves, electromagnetic or acoustic excitations or evanescent electromagnetic waves near a boundary, guided waves in optical fibers… From symmetry and conservation laws, we obtain, in the case of symmetric scatterers, the general form of the transfer matrix in terms of four independent real parameters. For ID-periodic lattices of identical scatterers, we show that leakage vanishes at the band edge: this coherent effect stems from the complete destructive interference between the converted radiations at each scatterer. This result demonstrates that coherent leakage is deeply different from a usual «dissipation» effect. Finally, we discuss the competition between Anderson localization and coherent leakage in the presence of disorder. Near the band edges and in the presence of disorder, the «attenuation length» due to the leakage is much larger than the localization length. We suggest an experimental situation where these effects could be observed Etude generale de la propagation d'ondes guidees en presence d'inhomogeneites et de diffuseurs. Exemples: ondes acoustiques de surface, excitations electromagnetiques et acoustiques, onde evanescentes proches d'une frontiere, ondes guidees dans les fibres optiques

Broadband LiTaO 3 guided-wave TE–TM mode converter

Abstract: A guided-wave TE to TM mode converter was demonstrated in LiTaO (3). The input mode is Bragg scattered from a collinear electrooptically induced wave of off-diagonal polarizability which couples the TE and TM modes. Compared with LiNbO(3), LiTaO(3) provides a smaller birefringence and thus a larger phase match period and larger optical bandwidth. A novel electrode structure allowed a four-phase drive of the polarizability wave with only two applied voltages. TE-TM mode conversion efficiency of 95% was demonstrated with a 103-A optical bandwidth. Operation as a frequency shifter was confined to low conversion efficiencies due to fringing fields.

Guided optics in rotating dielectric media

Abstract: The present developments of passive optical gyros using all fibre optical paths rise the question of guided modes in rotating dielectric guides. In the present paper, a general-relativistic approach to internal electromagnetic experiments in a rotating frame is proposed. Introduction of the 3-space orthogonal to the rotating observer’s worldline is achieved by means of an orthogonal tetrad which enables us to derive Sagnac-Maxwell equations. The so-called Sagnac effect for a light ray along a closed path is immediately obtained, then the Sagnac phase is seen to be the same for an infinitely thin mode, and finally for a finite guided wave when applied to the mean point of the transverse power density chart of the mode.

Viscous fluid effects on guided wave propagation in a borehole

Abstract: In order to investigate the effect of borehole fluid viscosity on the attenuation and dispersion of the guided waves present in full waveform acoustic logs, the problem of wave propagation in a borehole containing a viscoelastic fluid surrounded by an infinite elastic formation is solved using boundary layer theory. The results indicate that the losses due to viscous drag along the borehole wall are a small component of the overall guided wave attenuation for the frequencies of interest in full waveform acoustic logging (2–15 kHz) and for reasonable viscosity values (1–1000 cP). These losses, however, can be significant at low frequencies. In addition, the variations in viscosity have a negligible effect on the guided wave dispersion for this range of frequency and viscosity. These findings indicate that friction between grains in fluid suspension may be the dominant attenuation mechanism in the drilling fluids present in boreholes.

Modeling of a focusing grating coupler using vector scattering theory

Abstract: The diffraction efficiency of a focusing grating coupler has been modeled using a vector scattering treatment. The diffracted field components have been solved for the case of a TE-polarized guided wave. The amplitudes have been compared with those at the exit pupil of an aplanatic lens. The field distribution at the focal plane has been computed for field angles of 0 and 15°.

Low-power, single-interface guided waves mediated by high-power nonlinear guided waves: TE case

Abstract: The dispersion relation for a low-power (probe) TE-polarized wave guided by an interface between a linear and nonlinear medium was derived and investigated numerically as a function of the power of a high-power (pump), TE-polarized nonlinear wave guided by the same interface. The birefringence induced by a Kerr-type nonlinearity leads to a difference between the dispersion relations for pump and probe beams propagating at right angles to each another.

Guided - Wave Devices Based On Two - Mode - Interference

Abstract: The basic element of a two - mode - interference (TMI) device is the two - moded waveguide, which is coupled adiabatically to two single - mode feeding waveguides at the input and output ports, respectivly. As an alternative to the directional coupler (DC), the TMI - principle offers the potential of realising a new class of guided - wave devices: electrooptic switches like the X - switch, wavelength multiplexers and demultiplexers with a wavelength periodic characteristic, passive polarization splitters, as well as polarization independent switches.

Precise control of phase constant of optical guided-wave devices by loading Langmuir-Blodgett films

Abstract: A Langmuir-Blodgett film is used as a cover layer of single mode waveguide to precisely control the phase constant of the guided-mode. The change of phase constant caused by the cover layer is evaluated by measuring the retardation between the two arms of the ion-exchanged glass waveguide Mach-Zehnder interferometer, a part of which is loaded by Langmuir-Blodgett films. A monolayer of cadmium stearate has varied the phase constant on the order of 10/sup -6/. This method can be used to adjust the phase difference or shift to tune the performance of guided-wave devices such as directional couplers and modulators. >

Approximate analysis of surface acoustic wave Delta nu / nu waveguide with general anisotropy

Abstract: The authors present an approximate analysis of guided waves in a SAW (surface acoustic wave) Delta nu / nu waveguide with general anisotropy. The proposed analysis is performed under the assumption that fields in the guiding and surrounding regions can be expressed in terms of a linear combination of variable-crested surface wave solutions for the unbounded metallized or free surface having a common wave number in the propagation direction. Specifically, the expression is developed for an eigenvalue equation of the guided wave solution based on the scattering analysis of the variable-crested waves at the metal/free surfaces. Numerical results on dispersion curves and field distributions of the guided on various anisotropic substrates are shown. A number of peculiar properties due to the anisotropy are demonstrated. The results of the accurate analysis based on the integral equation method are also shown, to verify the effectiveness of the proposed analysis. >

Frequency shifter for medium infrared range wave

Abstract: A frequency shifter to shift the frequency of a guided wave in the medium infrared range comprises: an optical guide, formed by semiconducting materials, on the surface of which a diffraction grating is created by carriers photo-induced by a periodic illumination. standard optic means projecting, on the surface of the guide, two wave beams having different frequencies in the near infrared or visible range, to produce, by interference, a periodic illumination of the surface of the guide. This illumination induces photocarriers constituting a diffraction grating which is in translational motion at constant speed. This motion shifts the frequency of the diffracted wave by Doppler effect.

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

Abstract: 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.