Abstract: Silveirinha and Engheta have recently proposed that electromagnetic waves can tunnel through a material with an electric permittivity ($ϵ$) near zero (ENZ). An ENZ material of arbitrary geometry can thus serve as a perfect coupler between incoming and outgoing waveguides with identical cross-sectional area, so long as one dimension of the ENZ is electrically small. In this Letter we present an experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel. The ENZ channel consists of a planar waveguide in which complementary split ring resonators are patterned on the lower surface. A tunneling passband is found in transmission measurements, while a two-dimensional spatial map of the electric field distribution reveals a uniform phase variation across the channel---both measurements in agreement with theory and numerical simulations.

Abstract: A model is developed for a parallel-plate waveguide formed by graphene. The graphene is represented by an infinitesimally thin, local two-sided surface characterized by a surface conductivity obtained from the Kubo formula. Maxwell’s equations are solved for the model fields guided by the graphene layers. It is shown that despite the extreme thinness of its walls, a graphene parallel-plate waveguide can guide quasi-transverse electromagnetic modes with attenuation similar to structures composed of metals, while providing some control over propagation characteristics via the charge density or chemical potential. Given the interest in developing graphene electronics, such waveguides may be of interest in future applications.

Abstract: This paper presents an investigation on a single-mode-multimode-single-mode fiber structure. A one-way guided-mode propagation analysis for the circular symmetry waveguide is employed to model the light propagation and the approximated formulations are derived and evaluated concerning the accuracy. Phase conjunction of the multimode interference within the fiber structure is revealed. A simple way to predict and analyze the spectral response of the structure is presented through the space to wavelength mapping with the derived approximated formulations. The prediction of spectral response is verified numerically and experimentally.

Abstract: A novel electro-optic silicon-based modulator with a bandwidth of 78GHz, a drive voltage amplitude of 1V and a length of only 80µm is proposed. Such record data allow 100Gbit/s transmission and can be achieved by exploiting a combination of several physical effects. First, we rely on the fast and strong nonlinearities of polymers infiltrated into silicon, rather than on the slower free-carrier effect in silicon. Second, we use a Mach-Zehnder interferometer with slotted slow-light waveguides for minimizing the modulator length, but nonetheless providing a long interaction time for modulation field and optical mode. Third, with this short modulator length we avoid bandwidth limitations by RC time constants. The slow-light waveguides are based on a photonic crystal. A polymer-filled narrow slot in the waveguide center forms the interaction region, where both the optical mode and the microwave modulation field are strongly confined to. The waveguides are designed to have a low optical group velocity and negligible dispersion over a 1THz bandwidth. With an adiabatic taper we significantly enhance the coupling to the slow light mode. The feasibility of broadband slow-light transmission and efficient taper coupling has been previously demonstrated by us with calculations and microwave model experiments, where fabrication-induced disorder of the photonic crystal was taken into account.

Abstract: We exploit here the dramatic field enhancement caused by energy squeezing and tunneling (i.e., 'supercoupling') in metamaterial-inspired ultranarrow waveguide channels with near-zero effective permittivity in order to sense small permittivity variations in a tiny object. The supercoupling effect is accurately modeled analytically and closed-form expressions are derived to describe the presence of defects or permittivity perturbations along the channel. Applications for tailoring its pass-band frequency and for high-Q sensing are proposed at microwave frequencies.

Abstract: Recent progress in quantitative ultrasound (QUS) has shown increasing interest toward measuring long bones by ultrasonic guided waves. This technology is widely used in the field of nondestructive testing and evaluation of different waveguide structures. Cortical bone provides such an elastic waveguide and its ability to sustain loading and resist fractures is known to be related to its mechanical properties at different length scales. Because guided waves could yield diverse characterizations of the bone's mechanical properties at the macroscopic level, the method of guided waves has a strong potential over the standardized bone densitometry as a tool for bone assessment. Despite this, development of guided wave methods is challenging, e.g., due to interferences and rnultiparametric inversion problems. This paper discusses the promises and challenges related to bone characterization by ultrasonic guided waves.

Abstract: Following our recent interest in metamaterial-based devices supporting resonant tunneling, energy squeezing, and supercoupling through narrow waveguide channels and bends, here we analyze the fundamental physical mechanisms behind this phenomenon using a transmission-line model. These theoretical findings extend our theory, allowing us to take fully into account frequency dispersion and losses and revealing the substantial differences between this unique tunneling phenomenon and higher-frequency Fabry-Perot resonances. Moreover, they represent the foundations for other possibilities to realize tunneling through arbitrary waveguide bends, both in E and H planes of polarization, waveguide connections, and sharp abruptions and to obtain analogous effects with geometries arguably simpler to realize.

Abstract: In general, in accordance with an exemplary aspect of the present invention, a low-loss interface for connecting an integrated circuit such as a monolithic microwave integrated circuit to an energy transmission device such as a waveguide is disclosed. The interface comprises an isolation wall placed between an input and output region of an integrated circuit to reduce ripple and isolate the waveguide cavity from the monolithic microwave integrated circuit circuitry. The interface further comprises a turning screw or other similar member that is configured to closely match the impedance of integrated circuit 11 with the impedance at interface 10 to further reduce loss.

Abstract: We characterize silicon waveguide based wavelength converters using a commercial semiconductor optical amplifier (SOA) based wavelength converter as a benchmark. Conversion efficiency as high as -5.5 dB can be achieved using a 2.5 cm long sub-micron silicon-on-insulator rib waveguide. Comparison with the SOA reveals that silicon offers broader conversion bandwidth, higher OSNR, and negligible channel crosstalk. The impact of two-photon absorption and free carrier absorption on the conversion efficiency and the dependence of the efficiency on the rib waveguide dimensions are investigated theoretically. Using a nonlinear index coefficient of 4x10(-14) cm(2)/W for silicon, we obtain good agreement between simulations and measurements.

Abstract: We study nonlinear Cerenkov radiation generated from a nonlinear photonic crystal waveguide where the nonlinear susceptibility tensor is modulated by the ferroelectric domain. Nonlinear polarization driven by an incident light field may emit coherently harmonic waves at new frequencies along the direction of Cerenkov angles. Multiple radiation spots with different azimuth angles are simultaneously exhibited from such a hexagonally poled waveguide. A scattering involved nonlinear Cerenkov arc is also observed for the first time. Cerenkov radiation associated with quasi-phase matching leads to these novel nonlinear phenomena.

Abstract: Microfabricated acoustic crystals have been designed and experimentally verified. The acoustic crystals are realized by including tungsten (W) scatterers in a SiO2 matrix. Wide frequency ranges where acoustic waves are forbidden to exist (acoustic bandgaps, ABG) are formed due to the large acoustic impedance and mass density mismatch between W and SiO2. The acoustic crystal structures are fabricated in a 7-mask process that features integrated aluminum nitride piezoelectric couplers for interrogating the devices. Acoustic crystals in a square lattice have been measured at 67 MHz with greater than 30 dB of acoustic rejection and bandwidths exceeding 25% of the midgap. Single and multimode acoustic waveguides have been realized by defecting the acoustic crystals through removal of a subset of the W scatterers. These waveguides achieve relative transmission of up to 100% for the propagating modes.

Abstract: A system for monitoring an area comprising at least one waveguide such as an optical fiber having at least one Bragg grating sensor integrated in the waveguide; a plurality of light sources adapted to emit light into both ends of said waveguide; and at least one detector adjusted to detect light at each end of the waveguide,. The Bragg grating sensors may enable sensing at least one type of physical stimuli such as strain or temperature changes by changing at least one feature of the light they reflect, wherein the light sources and detectors may be adapted to be set selectively into operation according to the light detected by the detectors.

Abstract: The novel folded substrate-integrated waveguide (FSIW) is 50% narrower than the substrate-integrated waveguide, but both have similar propagation characteristics. This paper derives the analytical formulas of propagation and cutoff characteristics of the FSIW, as well as the formulas to calculate the width and gap of the central metal septum. Very good agreements (<2% error) are observed among the results of the theoretical formulas, numerical simulations, and hardware experiments over wide frequency and parameter ranges.

Abstract: We propose new all-optical logic gates containing a local nonlinear Mach-Zehnder interferometer waveguide structure. The light-induced index changes in the Mach-Zehnder waveguide structure make the output signal beam propagate through different nonlinear output waveguides. Based on the output signal beam propagating property, various all-optical logic gates by using the local nonlinear Mach-Zehnder waveguide interferometer structure with two straight control waveguides have been proposed to perform XOR/NXOR, AND/NAND, and OR/NOR logic functions.

Abstract: Low profile, side-emitting LEDs are described. The LEDs are used in very thin backlights for backlighting an LCD. In one embodiment, the backlight comprises a solid transparent waveguide (66) with at least one opening in the waveguide containing an LED (10) proximate to one edge. To smooth out a clover-shaped or batwing brightness profile inherently generated by a rectangular side-emitting LED within a smooth-sided rectangular opening in the waveguide, depending on the orientation of the LED, the sidewalls (68) of the opening are made to have varying angles along the length of each sidewall to vary the refraction angle of light along the sidewall. Additionally, if a plurality of LEDs are used in the backlight, the orientations of the openings alternate to create a more uniform brightness profile (64) in the waveguide (62).

Abstract: InP/GaInAsP square-resonator microlasers with an output waveguide connected to the midpoint of one side of the square are fabricated by standard photolithography and inductively-coupled-plasma etching technique. For a 20-mu m-side square microlaser with a 2-mu m-wide output waveguide, cw threshold current is 11 mA at room temperature, and the highest mode Q factor is 1.0 X 10(4) measured from the mode linewidth at the injection current of 10 mA. Multimode oscillation is observed with the lasing mode wavelength 1546 nm and the side-mode suppression ratio of 20 dB at the injection current of 15 mA. (C) 2008 Optical Society of America

Abstract: The concept of power waves gives more natural relations between incident and reflected power in a microwave network than the typically used traveling waves. The reflection coefficient for power waves directly describes the reflection of power whereas the reflection coefficient of traveling waves describes the reflection of the waves themselves. In this brief, new physical reasoning of power waves is given starting from the principle of conjugate matching. In addition, a new formula for the reference impedances for a two-port system is given such that the system is simultaneously conjugate matched for both ports.

Abstract: In this paper, we report on the first demonstration of monolithically integrated waveguide transitions in a submillimeter-wave monolithic integrated circuit (S-MMIC) amplifier module. We designed the module for a targeted frequency range of 300-350 GHz, using WR2.2 for the input and output waveguides. The waveguide module utilizes radial -plane transitions from S-MMIC to waveguide. We designed back-to-back radial probe transitions separated by thru transmission lines to characterize the module, and have incorporated the radial -plane transitions with an S-MMIC amplifier, fabricated monolithically as a single chip. The chip makes use of an S-MMIC process and amplifier design from the Northrop Grumman Corporation, Redondo Beach, CA, using 35-nm gate-length InP transistors. The integrated module design eliminates the need for wire bonds in the RF signal path, and enables a drop-in approach for minimal assembly. The waveguide module includes a channel design, which optimizes the -plane probe bandwidth to compensate for an S-MMIC width, which is larger than the waveguide dimension, and is compatible with S-MMIC fabrication and design rules. This paper demonstrates for the first time that waveguide-based S-MMIC amplifier modules with integrated waveguide transitions can be successfully operated at submillimeter-wave frequencies.

Abstract: As a novel interconnect and planar transmission line structure, the substrate integrated waveguide (SIW) is investigated in terms of its power handling capabilities (PHCs) including average and peak power handling capabilities. A heat transfer analysis based on ohmic and dielectric attenuation of SIW has been used to calculate the average power handling capability (APHC) while the maximum E-field derivation method has been selected to determine the peak power handling capability (PPHC). Results from the present investigations have shed light on some basic properties of SIW interconnects and related transmission line systems in a high-power operating environment and also can be used to analyze some application-oriented structures such as SIW bends. It is believed from the conclusions that an SIW interconnect can handle medium average power with extremely high peak power over microwave and millimeter-wave frequency bands.

Abstract: Evanescent coupling of light from glass channel waveguides into the whispering gallery modes of glass microspheres of radius 15µm and 100µm is studied experimentally at wavelengths near 1550nm. Fitting the positions, widths and heights of resonances in the experimental spectra to the characteristic equation for microsphere modes and to universal coupled microresonator theory, we establish sphere radius and index, identify mode numbers, and determine losses. The results provide detailed information for the design of optical devices incorporating microsphere resonators in planar lightwave circuits.

Abstract: We propose an optical transformation to bend electromagnetic waves by designing proper inhomogeneous and anisotropic materials, which are hereinafter referred to as metamaterials (MTMs). When the waveguide bends are filled with MTMs, the incident waves will pass through the bends without any reflections (for full-parameter MTMs) or with very small reflections (for simplified-parameter MTMs). When MTMs are placed in air, the incident waves will be bent to any designed directions. We also discuss the wave bending using layered homogeneous uniaxial MTMs, which can be easily realized using artificial structures.

Abstract: Metal-dielectric nanocavities constructed by filling a piece of nonlinear optical material into metal gap waveguides are introduced for realizing optical bistability in nanodomain. Finite-difference time-domain simulation reveal that such a structure can realize optical bistable effect with much weaker operating light power in a nanoscale nonlinear medium. We attribute it to the enhancement of local field intensity and nanoscale confinement of surface plasmon polaritons. Our results verify a feasible way for constructing nanoscale optical logical gates, switches, and all-optical transistors etc. for high density integration of optical circuits.

Abstract: A derivation of metamaterial blueprints for the reflectionless (perfectly matched) guiding of electromagnetic waves through waveguide bends is performed. The sensitivity of the response with respect to small perturbations in the associated constitutive tensors is examined.

Abstract: Northrop Grumman Corp. (NGC) has continued to develop a VE-based folded waveguide (FWG) technology as part of DARPA's terahertz imaging focal plane array technology (TIFT) source development program. The THz source consists of a thermionic electron gun, a FWG regenerative oscillator circuit, a depressed collector, and a 10 kG Nd-Fe-B permanent magnet solenoid to confine the electron beam. Significant improvements have been made to the compact THz source, increasing the output power, efficiency, and operational duty cycle.

Abstract: We demonstrate that terahertz microstrip-line waveguides can be used to measure absorption spectra of polycrystalline materials with a high frequency resolution (∼2 GHz) and with a spatial resolution that is determined by the microstrip-line dimensions, rather than the free-space wavelength. The evanescent terahertz-bandwidth electric field extending above the microstrip line interacts with, and is modified by, overlaid dielectric samples, thus enabling the characteristic vibrational absorption resonances in the sample to be probed. As an example, the terahertz absorption spectrum of polycrystalline lactose monohydrate was investigated; the lowest lying mode was observed at 534(±2) GHz, in excellent agreement with free-space measurements. This microstrip technique offers both a higher spatial and frequency resolution than free-space terahertz time-domain spectroscopy and requires no contact between the waveguide and sample.

Abstract: A study of the optical transmission of low-loss W1.5 photonic crystal waveguides built on silicon membranes and operating at telecom wavelengths is presented. The feasibility of performing all-optical switching is demonstrated for W1.5 waveguides coupled with L3 cavities, systems amenable for incorporation in on-chip devices. Switching of waveguide transmission is achieved by means of optical excitation of free carriers using a 2.5 ns pump laser. Experimental results are reproduced by finite-difference time-domain simulations which model the response of the finite system and band structure calculations describing the infinite, ideal one.