Abstract: We determine the threshold power for self-focusing collapse both in a bulk medium and in a hollow-core waveguide for various spatial profiles. We find that the threshold power for collapse in the waveguide is always equal to the lower-bound prediction for a bulk medium.

Abstract: Tightly confined, low-loss waveguides in highly nonlinear materials permit nonlinear optical interactions to occur over much shorter distances than do fibers The nonlinear interactions are further enhanced in resonators Both theory and experiment of enhanced four-wave mixing in micro-ring resonators are presented that can be used for many applications A conversion efficiency of 14% achievable with only 10-mW peak pump power is predicted under realizable conditions The experiment, the first one to the authors’ knowledge in nonlinear optics performed in microrings, shows, even in a lossy GaAs/AlGaAs ring, a 26-dB improvement in the conversion efficiency compared with that of an equivalent straight waveguide, in agreement with theory

Abstract: Waveguide propagation of sub-ps terahertz pulses in single-crystal sapphire fibers is reported. An incident THz pulse of approximately 0.6 ps duration undergoes considerable reshaping due to the absorptive and dispersive waveguide propagation, resulting in transmitted chirped pulse durations of 10–30 ps. Good agreement between theory and experiment is obtained by analyzing the propagation in terms of the single HE11 waveguide mode. The dominance of the single HE11 mode, despite the fiber dimensions allowing for multimode propagation, is attributed to the free-space to waveguide coupling.

Abstract: We proposed and demonstrated two different methods to split electromagnetic waves in three-dimensional photonic crystals. By measuring transmission spectra, it was shown that the guided mode in a coupled-cavity waveguide can be splitted into the coupled-cavity or planar waveguide channels without radiation losses. The flow of electromagnetic waves through output waveguide ports can also be controlled by introducing extra defects into the crystals. Our results may have an important role in the design of efficient power splitters in a photonic circuit.

Abstract: A new type of waveguiding mechanism in three-dimensional photonic band-gap structures is demonstrated. Photons propagate through strongly localized defect cavities due to coupling between adjacent cavity modes. High transmission of the electromagnetic waves, nearly 100%, is observed for various waveguide structures even if the cavities are placed along an arbitrarily shaped path. The dispersion relation of the waveguiding band is obtained from transmission-phase measurements, and this relation is well explained within the tight-binding photon picture. The coupled-cavity waveguides may have practical importance for development of optoelectronic components and circuits.

Abstract: We develop a model to treat coupling between guided modes in planar dielectric waveguides that have been textured in two dimensions with a thin surface grating The formulation is based on a general Green's-function technique that self-consistently determines the field in the surface grating due to the polarization there With simplifying approximations, this formalism is cast into a two-dimensional (2D) vector-coupled-mode theory that is more computationally efficient, and that gives considerable insight into the nature of mode coupling in 2D textured structures These models are applied, by way of example, to illustrate some interesting properties of leaky and bound modes that are coupled together by 2D periodic texture In particular we discuss the complex photonic band structure describing the dispersion, lifetimes, and polarization properties of the resonant states associated with the textured waveguide In our analysis we emphasize the fundamental differences between coupling in 2D textured waveguides and infinite 2D photonic crystals We also show that the vector-coupled-mode theory agrees well with the self-consistent formulation

Abstract: The hybrid boundary element method aimed at analyzing Lamb wave scattering from defects can provide us with an excellent numerical tool for tackling complicated mode conversion phenomena under waveguide thickness variation. In this paper, utilization of hybrid boundary element modeling for specific Lamb wave mode incidence situations with special energy distributions along the structural cross section is proposed for estimating reflection and transmission from various scatterers, such as a step discontinuity and tapered parts of a waveguide, etc. Interaction of individual Lamb wave modes with scatterers that represent arbitrary thickness variation along the direction of guided wave propagation is investigated by calculating the scattered fields for varying incident modes, frequency, and scatterer shape. The mode conversion phenomena through step discontinuity in a plate are also experimentally explored. The theoretical predictions of reflection and transmission by boundary element methods and the utility of dispersion curves are compared with experiments for specific modes. Results in this paper can be used to improve inspection sensitivity and penetration power for a variety of practical NDE applications, notably those in which thickness variation is found. In addition, the feasibility of inspecting sections located behind a waveguide thickness variation region and subsequent mode control will also be discussed.

Abstract: We present experimental and theoretical results of our recent work on the development of waveguide lasers using rare-earth-doped phosphate glasses An improvement has been achieved over previously reported waveguide laser results using the process of ion exchange in a commercially available Yb/Er-codoped phosphate glass composition We have demonstrated slope efficiencies near 30% with output powers approaching 200 mW for 1540 nm Fabry–Perot waveguide lasers These lasers are continuously tunable over approximately 70 nm In addition, Yb-doped Fabry–Perot waveguide lasers have been fabricated and tested These lasers operate near 1020 nm wavelength with slope efficiency of 67% We have also realized arrays of single-frequency distributed-Bragg-reflector (DBR) waveguide lasers operating near 15 μm by etching a grating in ion-exchanged waveguides Each laser in the array operates at a different wavelength The slope efficiencies as a function of launched pump power are 26% and the thresholds occur at approximately 50 mW of launched pump power Temperature tuning of the wavelengths is also demonstrated

Abstract: The present invention relates to feed structures for electromagnetic waveguides, cavities, antennas and other structures. A "feed structure" is an arrangement for electrical conductors used to transfer RF energy between any transmission lines and a waveguide. There are problems associated with designing and manufacturing conventional feeds. The present invention overcomes these problems by directly coupling an integrated circuit incorporating an RF circuit element to a waveguide, cavity, antenna or other structure. Coupling is achieved by an aperture formed in a ground plane of the integrated circuit and connected to a transmission line linked to the RF circuit element.

Abstract: Charged particles (21) suspended in a medium (20) such as FluorinertTM Electronic Liquid are used to electrophoretically control total internal reflection (TIR) at a retro-reflective surface formed on a high refractive index material. Prismatic structures (35, 32, 81) redirect ambient light from an overhead light source toward a display image and then from the image to the region in front of the image, yielding a high contrast reflective display. A transparent planar waveguide (36) front lights the display with sequential flashes of red, blue and green light to generate a full colour display. TIR can also be controlled at retro-reflective surfaces by means of a vapour-liquid phase transition, or by changing the absorption coefficient of a material using electrical, chemical and/or electrochemical methods.

Abstract: Optical resonators are vertically coupled on top of bus waveguides, and are separated from the waveguides by a buffer layer of arbitrary thickness. The vertical arrangement eliminates the need for etching fine gaps to separate the rings and guides, and reduces the alignment sensitivity between the desired position of the resonator and bus waveguides by a significant degree. The resonator and bus waveguides lie in different vertical layers, and each can therefore be optimized independently. A ring resonator can be optimized for higher index contrast in the plane, small size, and low bending loss, while the bus waveguides can be designed to have lower index contrast in the plane, low propagation losses, and dimensions that make them suitable for matching to optical fibers. The waveguides can also have any lateral placement underneath the ring resonators and are not restricted by the placement of the rings. Furthermore, with the resonators lying on the top layer of the structure, they are easily accessed for tuning and trimming.

Abstract: Three-dimensional opto-electronic modules having a plurality of opto-electronic (O/E) layers, with optical signals being routed between O/E layers within one or more three-dimensional volumes, are disclosed. In preferred embodiments, the O/E layers are disposed over and above one another with at least one of their edges aligned to one another. At least two of the O/E layers have waveguides with ends near the aligned edges. A plurality of Zconnector arrays are disposed between the O/E layers and within the three-dimensional volumes to provide a plurality of Zdirection waveguides. A first vertical optical coupler couples light from one waveguide in one O/E layer to a Z-direction waveguide, and a second vertical optical coupler couples the light from the Z-direction waveguide to a second waveguide in a second O/E layer. In further preferred embodiments, segments of the Z-connector arrays are held by a holding unit.

Abstract: An overview is presented of an experimental search for an ultrawide-band transmission channel with low dispersion and loss. Such a terahertz (THz) interconnect will soon be required by the insatiable demand for higher speed devices and wider bandwidth communication. Starting with the early optoelectronic generation and detection of single-mode, subpicosecond electrical pulses on coplanar transmission lines, their complete characterization by THz time-domain spectroscopy (THz-TDS) is described. The consequent discovery of phase-coherent Cherenkov radiation in the form of an electromagnetic shock wave from these propagating electrical pulses is discussed together with its dominant role in the large measured propagation loss of these pulses. Various techniques to reduce this radiation are presented. The importance of dielectric materials characterization is explained and illustrated by THz-TDS measurements of high T/sub c/ substrates. Newly obtained THz waveguide results are presented and compared to the performance of coplanar transmission lines.

Abstract: Apparatus for transmitting and receiving signals over a fiber-optic waveguide using different frequency bands of light, i.e. by wavelength division multiplexing. A plurality of signal couplers interfaces modulated signals onto the waveguide in separate optical frequency bands, and a plurality of signal probes forming a probe array at one or more places in the waveguide, receives the signals, which are subject to scrambling and distortion as a result of physical irregularities in the waveguide. A recovery system coupled to the signal probes effects recovery and separation of the received signals using cumulant computations based on cumulants of the fourth or higher even order.

Abstract: The properties of some purely bound plasmon-polariton modes guided by an asymmetric waveguide structure composed of a thin lossy metal film of finite width supported by a dielectric substrate and covered by a different dielectric superstrate are presented for what is believed to be the first time. The mode spectrum supported by these structures is quite different from the spectrum supported by corresponding asymmetric slab structures or similar finite-width symmetric waveguides. Unlike these limiting cases, the dispersion with film thickness exhibits an unusual oscillatory character that is explained by a “switching” of constituent interface modes. This mode switching is unique to asymmetric finite-width structures. Above a certain cut-off film thickness, the structure can support a long-ranging mode and its attenuation decreases very rapidly with decreasing film thickness, more so than the long-ranging mode in symmetric structures. Also, the cutoff thickness of the long-ranging mode is larger than the cutoff thickness of the long-ranging mode in the corresponding asymmetric slab waveguide, which implies that propagation along finite-width films is more sensitive to the asymmetry in the structure than propagation along a similar slab structure. Both of these results are potentially useful for the transmission and control of optical radiation.

Abstract: The fabrication and characterization of micromachined reduced-height air-filled rectangular waveguide components suitable for integration is reported in this paper. The lithographic technique used permits structures with heights of up to 100 /spl mu/m to be successfully constructed in a repeatable manner. Waveguide S-parameter measurements at frequencies between 75-110 GHz using a vector network analyzer demonstrate low loss propagation in the TE/sub 10/ mode reaching 0.2 dB per wavelength. Scanning electron microscope photographs of conventional and micromachined waveguides show that the fabrication technique can provide a superior surface finish than possible with commercially available components. In order to circumvent problems in efficiently coupling free-space propagating beams to the reduced-height G-band waveguides, as well as to characterize them using quasi-optical techniques, a novel integrated micromachined slotted horn antenna has been designed and fabricated, E-, H-, and D-plane far-field antenna pattern measurements at different frequencies using a quasi-optical setup show that the fabricated structures are optimized for 180-GHz operation with an E-plane half-power beamwidth of 32/spl deg/ elevated 35/spl deg/ above the substrate, a symmetrical H-plane pattern with a half-power beamwidth of 23/spl deg/ and a maximum D-plane cross-polar level of -33 dB. Far-field pattern simulations using HFSS show good agreement with experimental results.

Abstract: This paper presents novel types of polarizers that are composed of grooved circular waveguides. The presented polarizers are suitable for realizing high-performance and low-fabrication cost in the Ka-band and above because of simple structure. Accurate analysis and design of the polarizers are performed using full-wave mode-matching techniques applied to the circular-to-rectangular waveguide T-junctions and cross-junctions. Ka-band grooved circular waveguide polarizers fabricated with the aid of the analysis and design techniques have realized excellent performance without tuning elements.

Abstract: A method is proposed to measure the thickness of the air layer between the prism and the waveguide in a totally reflecting prism coupler. The coupling efficiency of a Gaussian beam from the prism into the waveguide can be calculated when the air-layer thickness (ALT) is known. To perform measurements of the indices and thicknesses of planar waveguides using the m-lines technique, it is necessary to have a good knowledge of the prism's characteristics and to accurately measure the angles. However, we show by means of an example that the small distance between the prism and the guide (i.e. the ALT) should be taken into account in order to achieve accurate measurements.

Abstract: We present the characteristics of radio propagation in a circular lossy waveguide whose walls are composed of earth soil materials with frequency-dependent properties. This type of structure is used to represent a radio link for an underground wireless communication channel such as a tunnel, mine shaft, or borehole. We present calculated results of the attenuation constant for various propagation modes in the soil waveguide structure for various soil constituents and moisture levels. Transverse field plots of the various modes for different soil types are also presented. Finally, it is shown that for small |k/sub 2/a| (where k/sub 2/ is the wavenumber in the soil and a is the radius of the waveguide) some modes in the waveguide disappear and a discussion of this behavior and how it relates to excitation problems is given.

Abstract: An optical phase modulator comprises a semiconductor rib wave guide having P and N doped regions forming a PN junction along the path of the rib with terminals for applying a reverse bias to the junction to extend a carrier depletion zone to alter the refractive index, the PN junction is offset from the central axis of the rib but on application of the reverse bias the depletion zone extends over a central axis of the waveguide.

Abstract: Neodymium-doped polyimide waveguides were studied for optical amplifier applications Photoluminescence at 890 nm, 106 μm, and 133 μm from neodymium ions in the polymer matrix was observed Optical gain of about 8 dB was measured at 106 μm in a 5-cm-long multimode channel waveguide Phase separation was observed in the doped polyimide Large scattering losses in the waveguides due to the phase separation were reduced by planarizing the layer of doped polyimide with another layer of undoped polyimide Such a waveguide amplifier has potential applications in lossless splitters, lossless fiber, and waveguide systems with large fanout

Abstract: Both a nonfocusing and a focusing preferential-order volume grating waveguide coupler were designed, fabricated, and tested. These volume grating couplers are designed to outcouple a 633-nm wave guided in an adjacent polyimide waveguide film. The slanted-fringe volume gratings are recorded holographically by the interference of two 364-nm waves. The dynamics of the holographic photopolymer HRF600X001 are investigated in relation to the interaction with the guided wave. The fabricated couplers exhibited a preferential coupling of 98%, a spatial coupling rate of 3.6 mm-1, and a coupling efficiency of 95%. The focusing grating coupler focused the outcoupled beam to a focal line with a full width at half-maximum of 10.49 µm located 25 mm above the grating.

Abstract: Numerical simulations of MHD wave propagation and coupling in a realistic magnetotail are presented. Fast mode waves are observed to disperse and couple resonantly to Alfven waves over a broad layer rather than on an isolated field line. Indeed, the layer is likely to be so broad as to include the entire tail lobe as well as the plasma sheet boundary layer (PSBL). It appears that small k y modes (where k y is the cross-tail wave number) will provide the most efficient coupling as they will tend to propagate along the magnetotail field lines rather than across them and out of the tail boundaries. (Moreover, it is only small k y fast modes that will be able to penetrate the lobe.) Alfven waves in the PSBL are shown to phase mix rapidly resulting in strong field-aligned currents with an equatorward phase motion. These properties are in agreement with observations of optical auroral emissions. The lobe Alfven waves do not phase mix, and are not expected to excite optical emissions. They may, however, provide a significant ponderomotive force and could account for the transport of oxygen ions from the ionosphere into the distant tail lobes.

Abstract: We discuss the reflection of thermoelastic plane waves at a solid half-space nearby a vacuum. We use the generalized thermoelastic waves to study the effects of one or two thermal relaxation times on the reflection plane harmonic waves. The study considered the thermal and the elastic waves of small amplitudes in a homogeneous, isotropic, and thermally conducting elastic solid. The expressions for the reflection coefficients, which are the ratio of the amplitudes of the reflected waves to the amplitude of the incident waves are obtained. It has been shown, analytically, that the elastic waves are modified due to the thermal effect. The reflection coefficients of a shear wave that incident from within the solid on its boundary, which depend on the thermoelastic coupling factor and included the thermal relaxation times, have been found in the general case. The numerical values of reflection coefficients against the angle of incidence for different values of thermal relaxation times have been calculated and the results are given in the form of graphs. Some special cases of reflection have also been discussed, for example, in the absence of thermal effect our results reduce to the ordinary pure elastic case.

Abstract: A tunable external cavity semiconductor laser incorporating a tunable Bragg grating, including: a semiconductor gain medium; an elongated tuner housing having a tuner housing head and having a tuner housing foot, the tuner housing head and tuner housing foot being rigidly connected; a span of waveguide having a Bragg grating, for receiving the source light and for providing in turn the reflected light, and having a waveguide head and a waveguide foot, the waveguide head abutting the tuner housing head and the waveguide foot disposed toward the tuner housing foot; a piezoelectric crystal or other device or arrangement for providing a compressive force, disposed so as to abut the waveguide foot and also to abut the tuner housing foot, the means for applying a compressive force for exerting a compressive force on the span of waveguide along the direction of the axis of the span of waveguide, the compressive force being sufficient to alter the grating so as to affect the wavelength of light reflected by the grating. In some applications, the waveguide includes sections of different thicknesses, each having a sampled grating, the two sampled gratings being created so that at any given compressive force exerted by the piezoelectric crystal, the two gratings reflect at most one wavelength in common. The tunable laser in such an application therefore behaves as a stepped tunable laser.

Abstract: A laser-cooled neutral-atom beam from a low-velocity intense source is split into two beams while it is guided by a magnetic-field potential. We generate our multimode beam-splitter potential with two current-carrying wires upon a glass substrate combined with an external transverse bias field. The atoms are guided around curves and a beam-splitter region within a 10-cm guide length. We achieve a maximum integrated flux of 1.5×105 atoms/s with a current density of 5×104 amp/cm2 in the 100‐µm-diameter wires. The initial beam can be split into two beams with a 50/50 splitting ratio.

Abstract: A waveguide-based sensing system includes a plurality of waveguides (16) secured within a waveguide holder (12). Each waveguide has a sensing surface (18) with attached analyte recognition elements. The end faces (22, 24) of the sensing surfaces are perpendicular (or at least approximately perpendicular) to the sensing surfaces. The sensing surfaces are directly excited by light (20) directed normal thereto and emit optical signals responsive to the presence of an analyte. These optical signals are coupled into waveguides. The optical signals travel along the length of the waveguides. The integrated optical signals emitted from the end surfaces of the fibers are then detected and analyzed.