Showing papers on "Guided wave testing published in 1987"

Nonlinear pulse propagation in a monomode dielectric guide

Abstract: We derive the nonlinear wave equation for an envelope of an electromagnetic wave in a monomode dielectric waveguide. Concrete examples are given for a single-mode optical fiber where the coefficients of resultant nonlinear Schrodinger equation with higher-order dispersion and dissipation (both linear and nonlinear) are given in terms of properties of the eigenfunction of the guided wave as well as of the material nonlinearity and dispersion. Using a newly-developed perturbation method, we show that the higher-order dispersions (linear and nonlinear) perserve the profile of a single soliton but to split up a bound N soliton ( N \geq 2 ) into individual solitons with different heights which propagate at different velocities. We also show that the higher-order nonlinear dissipation due to the induced Raman effect downshifts the carrier frequency of a single soliton in proportion to the distance of propagation and to the fourth power of the soliton amplitude.

Guided-wave reflectometry with micrometer resolution.

Abstract: We describe a new type of optical reflectometry which is useful in testing single-mode lightguide systems. This technique uses a scanning Michelson interferometer in conjunction with a broadband illuminating source and cross-correlation detection. High resolution is achieved through the limited coherence of the backscattered radiation. With this approach it is possible to distinguish scattering centers separated by only a few micrometers. In some cases loss may be estimated for components in the transmission path of a test lightguide. The basic principles of this diagnostic technique, along with some performance characteristics, are illustrated for an all-fiber reflectometer. We also discuss several laboratory applications which serve to demonstrate the resolution capabilities of this measurement concept.

Exact dispersion relations for transverse magnetic polarized guided waves at a nonlinear interface.

Abstract: We derive exact dispersion relations for transverse magnetic polarized guided waves at an interface between either a linear dielectric or a metal and a nonlinear dielectric. The nonlinearity is taken to be a Kerr-type nonlinearity. Numerical results are presented for the dielectric–metal case.

Optical modulation apparatus and measurement method

Abstract: In an optical micromechanical method for changing the phase of guided waves and a measurement method for measuring very small mechanical displacements and/or mechanical forces or pressures, including the pressure of sound waves and ultrasonic waves, and/or accelerations, the distance d between a section (1') of an optical waveguide (1) in an integrated optic or fibre optic circuit and a phase-shifting element (5) separated from said section (1') by a gap (4) is varied by forces (6) or by thermal expansion due to changes in temperature. The phase of the guided wave (3) is thereby modulated, and reciprocally the changes in distance d and hence small mechanical displacements and the forces (6) which produce them are determined from the measured phase changes.

Non-invasive temperature monitor

Abstract: A non-invasive temperature monitoring apparatus used in association with a guided wave means (17, 18) that may be for the purpose of sterilization and that is adapted for microwave heating of a substance that is absorptive at microwave frequencies and that is held in some type of means that is transparent at microwave frequencies. The apparatus comprises a length of waveguide (40). A coupling aperture (42) is defined in the guided wave means (17). The length of waveguide (40) is supported with one end (44) thereof about the coupling aperture (42). A microwave radiometer (54) detection circuit is also coupled from the length of waveguide (40) for detecting on a continuing basis the temperature of the substance which is usually liquid being heated by the microwave energy.

Demonstration of optical bistability with a nonlinear prism coupler

Abstract: A guided wave is launched through a nonlinear prism coupler whose prism‐waveguide gap is filled with a liquid crystal. We observed that the intensity of the excited guided wave exhibits optical bistability when the incident intensity is modulated. This result, which is rather surprising when compared to recent theoretical predictions, is shown to arise from a thermal averaging process in the liquid crystal.

Guided-Wave Modes in Cylindrical Optical Fibers

Abstract: This paper proposes a logical and simple approach to the mode designations in a cylindrical optical fiber. An important approximation is introduced in the mathematical analysis to simplify the characteristic equation. Mode enumerations, field distributions, and propagation constants for some lower order modes are discussed and illustrated. The justification of using the linearly polarized mode designation is illustrated.

All‐optical guided‐wave Mach–Zehnder switching device

Abstract: We propose and analyze an all‐optical switching device on a nonlinear Mach–Zehnder waveguide interferometer. The nonlinear medium is modeled as a two‐level system to take saturation and attenuation effects into account.

Experimental study of a ZnO modulator using guided wave resonance

Abstract: A novel type of electro‐optic (EO) modulator using guided wave resonance in a planar zinc‐oxide waveguide is presented. The device is studied as a bulk EO modulator. We report experimental results concerning the determination of the coefficients of the EO tensor of the ZnO layer.

Power-dependent attenuation of TE waves propagating in optical nonlinear waveguiding structures

Abstract: Some aspects of the power-dependent attenuation of TE waves guided by structures consisting of an optical linear thin film (Corning 7059 glass) deposited onto the surface of a substrate (glass doped with CdS x Se 1-x semiconductor) exhibiting both positive and negative nonlinearities at two different wavelengths are studied numerically. It is shown that even a weak attenuation will strongly affect effective refractive index, phase, and field distribution of the guided wave. Depending on the sign of nonlinearity, the propagated wave will progressively shift into or out of the substrate for positive and negative nonlinearity, respectively.

Quasi-optics of the coupling of guided modes in two parallel, identical dielectric waveguides

Abstract: The coupled-mode equations governing the interaction of two guided modes in a pair of parallel, identical dielectric waveguides are deduced by a quasi-optical technique that also yields an elegant expression for the attenuation coefficient of the guided wave owing to losses in the various spatial regions.

Guided wave characteristics of metal-clad graded-index planar optical waveguides: Analytical approach

Abstract: The complex eigenvalue equations of metal-clad graded-index waveguides are generally solved by numerical methods. The role of waveguide and material parameters in determining mode dispersion and attenuation becomes difficult to elucidate. We describe a perturbative method of solution which is suited to the class of waveguide in which the guided field is described analytically. Mode dispersion and attenuation are explicitly obtained. Applications to three commonly used waveguide models demonstrate the accuracy of our approach in comparison to numerically obtained results.

Inversion of borehole guided wave amplitudes for formation shear wave attenuation values

Abstract: Formation shear wave attenuation (Qβ−1) and borehole fluid attenuation (Qƒ−1) values are estimated from the guided wave arrivals in full waveform acoustic logs. The use of guided waves avoids the problem of head wave geometrical spreading losses. Attenuation estimates are obtained from the inversion of guided wave spectral ratios using analytic partition coefficient expressions. The guided wave amplitude ratios are measured at uniformly spaced frequencies within a selected frequency window containing the pseudo-Rayleigh and Stoneley waves. Inversion of synthetic data from an open hole geometry results in Q estimates within 2–3% of the actual values. Inversion of cased hole synthetic data gives fluid Q and cement layer Q values within 2–3% of the actual values, but the formation shear wave Q estimate is in error by about 25% due to difficulty in identifying the pseudo-Rayleigh wave cutoff frequency from the amplitude spectra. Synthetic data results also indicate that the Q estimates are very sensitive to errors in any of the parameters that affect the partition coefficient calculations, such as the borehole fluid velocity or borehole radius. Application of the method to real data recorded in open boreholes provides reasonable results, but noise increases the variance of the Q estimates.

Low-loss broadband LiNbO 3 guided-wave phase modulators using a titanium/magnesium double-diffusion method

Abstract: Titanium-diffused LiNbO3 phase modulators are indispensable elements for high-bit-rate PSK coherent systems which have an advantage in that they have higher receiver sensitivity.1 Efficient fiber-LiNbO3 waveguide coupling is required to avoid sacrificing this advantage. The titanium/magnesium double-diffusion method.2 which gives good mode match to the fiber, is an excellent method to reduce fiber-waveguide coupling loss. However, it is likely that the drive voltage becomes higher for active devices such as phase modulators, because waveguides are buried by using this method.

Efficiency of guided wave acoustooptic interaction for selected cuts in LiNbO3

Abstract: The efficiency of thin film acoustooptic modulators in LiNbO3 is investigated theoretically in order to select the optimum crystal cut, SAW propagation direction and optical polarization. For a well concentrated optical field x-cut LiNbO3, z-propagating SAW and TE polarized light offers best performance for broadband modulators. In the Appendix parameters of several SAWs on the free surfaces of LiNbO3 were determined by numerical analysis using acoustic field theory and the quasi static electric field approximation. Complete sets of parameters are given for calculation of SAW fields related to the magnitude of complex mechanical power flow.

Electromagnetic resonance enhanced photoabsorption in planar metal–oxide–metal tunnel junction detectors

Abstract: We present calculations of surface plasmon and guided wave enhanced light absorption in the metal electrodes of planar aluminum–aluminum oxide–silver and aluminum–aluminum oxide–aluminum tunnel junctions. We consider excitation, under conditions of attenuated total reflection, of both the ‘‘fast’’ and ‘‘slow’’ surface plasmons of the junction, and of TE and TM guided modes supported by a dielectric film adjoining the junction. We find that >97% absorption may be obtained at resonance in a single electrode of a practical device, the thickness of which is only a fraction of the expected photocarrier mean free path, and show how the angular width of the absorption peak may be varied by changing the adjacent dielectric media. We also show how resonant absorption may be used in a biased planar device for the detection of radiation at normal incidence.

Poynting vector in a uniaxially birefringent multilayered system.

Abstract: Calculations of the Poynting vector in a uniaxially birefringent multilayered system are presented. Such calculations are then used to illustrate results from a system involving a liquid crystal layer aligned between silver films and observed using attenuated total reflection. Excitation of surface plasmon-polariton and guided wave resonances within the structure provide for highly structured reflectivity and transmissivity responses. Detailed analysis of the optical response of the layered structure are presented elsewhere. In this work the Poynting vector fields for several of the resonant modes are examined.

Surface-guided nonlinear TM waves in planar waveguides

Abstract: The propagation of strongly nonlinear TM surface-guided waves in media controlled by a self-focusing third-order optical, unsaturated nonlinearity is analysed theoretically. In this theory both the amplitude and the wave number of the guided wave are power dependent. The reasons for studying these waves are explained and it is emphasised that strong nonlinearity can lead to a number of device applications. Although such devices are not simulated here, a number of planar structures that are of potential device interest are discussed. A mathematical theory is presented that is both free of previous approximations and capable of dealing with many types of nonlinear mechanisms. The waveguide structures that are considered are a single interface between semi-infinite linear and nonlinear media, a linear guide symmetrically bounded by self-focusing nonlinear media and two linear waveguides coupled through a nonlinear medium. The exact theory quickly leads to equations that can only be solved numerically but some degree of analytical progress is reported here for the single-interface case. Two methods of solution are presented, one based on the first integral of the nonlinear wave equation and the other based on a spline collocation numerical method. Full numerical results are given in the form of power variation with effective wave index and a number of sample field distributions. The results are especially interesting in connection with the structures that possess negative dielectric components and the superwaves of the nonlinearly coupled guides. In the former, maxima, minima and negative power regions arise. In the latter, for a critical coupling distance, there exists a region of guide index for which the power flow down the guide is approximately constant

Optical modulation and measurement process.

Abstract: In an optical micromechanical process for changing the phase of guided waves for the purpose of modulating phase or intensity, and/or for switching guided optical waves between various outlets, and/or for deflecting optical waves, and/or for changing the resonance frequencies of frequency filters and resonators, and a measurement process for measuring very small mechanical displacements and/or mechanical forces or pressures, including the pressure of sound waves and ultrasonic waves, and/or accelerations, the distance d between a section (1') of an optical wave guide (1) in an integrated optic or fibre optic circuit and a phase-shifting element (5) separated from said section (1') by an intermediate space (4) is varied by forces (6) or by thermal expansion due to changes in temperature. The phase of the guided wave (3) is thereby modulated, and reciprocally the changes in the distance d and hence small mechanical displacements and the forces (6) which produce them are determined from the measured phase changes.

Analysis of the reflection grating couplers for waves at oblique incidence

Abstract: A perturbation analysis of a reflection grating for waves at oblique incidence is given. Three canonical equations governing the behavior of the reflection grating are systematically deduced, and from them the power-conservation principle and reciprocity are established. The characteristics of the output coupler are obtained with particular reference to both the direction and the polarization of the radiated waves. The important features of an input coupler are investigated with particular emphasis on the direction and the polarization of the incident wave and the length of the grating that lead to the maximum of the input-coupling efficiency. The guided wave can have its electric or magnetic field polarized normal to its sagittal plane, and the grating can be incorporated either on the conducting surface or on the film-cover interface. The relative merits of these four different schemes of operation of the reflection grating are discussed with reference to their applications as output and input couplers.

Spectroscopy with Ultrashort Electrical Pulses

Abstract: Recently optoelectronic techniques have been used to generate and detect subpicosecond electrical pulses on coplanar transmission lines.[1,2] The frequency bandwidth of these short electrical pulses ranges up to 1 THz and covers an important part of the far infrared energy spectrum from 0 to 30 cm-1, in which can be found the gap frequencies of superconductors, magnetic excitations, and the far infrared modes of lattices and molecules. With the proper generation geometry, these pulses propagate as a single mode excitation of the transmission line, and the pulse reshaping is determined by the frequency dependent dielectric response of the transmission line materials. These features, plus the fact that the earlier observations showed that the subpicosecond pulses broadened to only 2.6 psec after propagating 8 mm on the transmission line, allow for the following spectroscopic applications of these guided wave electrical pulses. In this paper we will discuss the study of far infrared absorption in superconductors and some magnetic modes in rare-earth garnets.

Ultrasonic waveguide technique for detection of simulated corrosion wastages

Abstract: Elastic wave propagation in a bounded medium significantly differs from that in an unbounded medium. The bounded medium in the form of a cylinder acts like a solid waveguide directing the wave with its geometry. A continuous or a pulsed wave interacts with cylindrical boundaries producing mode-converted signals in addition to the backwall echo. The signals are received at constant time Intervals directly proportional to the diameter of a solid cylindrical object such as a bolt or an anchor stud. The Cylindrically Guided Wave Technique (CGWT) makes intelligent use of the mode-converted signals, or trailing pulses, to detect corrosion wastages in cylindrical objects.

Mode Separation And Switching In Multichannel Branching Optical Waveguides

Abstract: A multimode channel waveguide that branches into several single-mode channels can route each of the modes of the multimode waveguide into a different single-mode channel. Such branches are useful for performing a variety of functions in guided wave optoelectronic devices. The two basic functions on which such devices rely are routing and its inverse, selective mode excitation. (For example, switching is time-dependent routing.) We describe the fundamentals of routing and selective mode excitation, and then analyze the performance of proposed two-and three-channel optical switches using parameters appropriate for GaAs. Because of the larger induced changes of refractive index that are possible in this material, we find that such switches can be substantially shorter than in other materials such as LiNbO 3 .

Guided wave communication system

Abstract: A guided wave communication system or network includes a head-end unit (15) which is coupled to one end of a bus-like wave guiding means (13, 16). Separate directional couplers (14,17) are disposed along the wave guiding means to couple lightwave or microwave signals either (a) into the bus-like wave guiding means (13) from separate transmitters (11), or (b) from a bus-like wave guiding means (16) to separate receivers (12). The directional couplers disposed along a guiding means each have a separate coupling coefficient which is optimized to only couple enough of the lightwave or microwave energy onto or from the associated guiding means so that either (a) the head-end unit receives a minimal signal power level from each transmitter or (b) the receivers receive a minimal signal power level from the head-end unit, respectively, to provide a predetermined bit error rate regardless of their distance from the head-end unit along the associated waveguiding means.

Trading coupling loss for modulation efficiency in electrooptic modulators

Abstract: Phase modulators utilizing the electrooptic effect in Li-NbO 3 are most efficient if the waveguide, and hence the guided mode, is positioned as closely as possible to the modulation electrode which is located at the surface of the crystal. However, placing the guided wave near the crystal surface tends to deform its shape so that the coupling loss between the waveguide mode and an optical fiber is increased. In this paper, we study the tradeoffs between coupling loss and modulation efficiency that result from moving the waveguide further below the crystal surface.