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Manipulating electromagnetic (EM) waves by plasma-dielectric-plasma (PDP) waveguides or plasma array structures presents significant potential in microwave signal processing, such as filtering, signal delay, and EM enhancement or shielding. Owing to the simple structure and easy fabrication, the waveguide with a tooth-shaped resonator has been a strong candidate as a filtering device. Based on our previous work focusing on U-shaped filtering excited by PDP waveguides with a double-teeth structure, in this work, the formation mechanism of a U-shape filtering spectrum is systematically explored by transmission line theory (TLT) with proper field distributions. The results indicate that the U-shape spectrum consists of boundary edges and a filtering stopband. The boundary edges are attributed to Fano-type resonance, and the enhanced destructive interference from double teeth is responsible for the stopband. Such an approach shows a specific and clear mechanism for the generated U-shaped spectrum. In addition, the theoretical analysis of double teeth without Fano-type resonances is rigorously demonstrated using TLT, which significantly contributes to bandwidth modulation of stopband filtering in theory. These results contribute to the understanding of the formation mechanism of a U-shaped spectrum from a gap plasmon waveguide (such as PDP or metal-insulator-metal (MIM)) with tooth-shaped resonators, offering a feasible direction for the optimization of filtering properties, as well as offering significant parameters for subsequent experimental design. [ABSTRACT FROM AUTHOR]

The laser wakefield acceleration in bubble regime is now a promising method for producing high-quality electron beams, which is crucial to the development of the next-generation compact and low-cost particle accelerators. In this paper, we demonstrate the possibility of controlling particle injection and electron beam quality in sub-petawatt laser pulse interaction with simple plasma waveguides with a radially step-like density profile. Fully relativistic particle-in-cell calculations for different laser intensities indicate that by considering a sufficiently low electron density for a central plasma channel to ensure both increased acceleration length and formation of a well-structured bubble, one can optimize the surrounding plasma density and central channel diameter to reach the best injection conditions and produce a high-quality monoenergetic electron beam with improved peak energy and reduced energy spread. Calculations are performed for 33 fs, 140–315 TW laser pulses interacting with a ∼2 cm long plasma waveguide. It is demonstrated that by using the proposed scheme in optimized conditions, monoenergetic electron beams with peak energies 3–4 GeV and energy spreads less than 1.5% can be obtained in a single acceleration length of 1.85 cm. The beam charge and conversion efficiency of laser energy into the beam energy were also enhanced to values around 195 pC and 14.7%, respectively. [ABSTRACT FROM AUTHOR]

Stable propagation of laser filamentation arrays paves new ways for cross‐scale manufacturing. Although a single filament or multiple filaments can be used for laser processing in transparent media, sustainable developments of higher throughput and lower energy consumption are always the pursuit. Here, a proof‐of‐concept approach is proposed in which cross‐scale manufacturing of 3D microstructures is realized via an ionization‐induced volume plasma grating. The volume plasma grating is generated by the noncollinear interaction of two batches of arrays of multiple filaments. The volume plasma grating cannot only regulate the distribution of multiple filamentation but also promote the intensity inside the filaments. By this approach, 3D microstructures are written by 1D sample translation. In addition, rapid fabrications of volume gratings and terahertz wire grid polarizers (THz WGPs) are demonstrated by laser modification using volume plasma grating. The characteristics of the fabricated THz WGPs are comparable to those of commercial ones. The limitations and future implementations of this approach are discussed. [ABSTRACT FROM AUTHOR]

In this paper, a plasmonic electro-optical encoder based on graphene at THz frequency is proposed. The surface plasmon polaritons (SPPs) in the graphene–insulator–metal structure are excited by an incident TM wave with a wavelength of 9.3 μm. Graphene plasma waveguides have extremely high confinement, relatively low losses, and high tunability. The switching mechanism is based on the application of an external voltage to locally change the chemical potential of the graphene for encoding. Setting the chemical potential to 1 eV allows SPPs to propagate while lowering the chemical potential to 0.1 eV prevents the SPPs from propagating. A 4 × 2 encoder with a minimum encoding extinction ratio (ER) of 37 dB, a maximum modulation depth (MD) of 99.99%, and a structure area of 0.8 μm2 is proposed based on the design rules and simulations using the finite-difference time-domain (FDTD) method. In terms of the obtained results, the proposed structure can be used in optical integrated circuits. [ABSTRACT FROM AUTHOR]

The paper proposes a method of controlled heating of a cylindrical plasma using the features of the Exceptional point. It is shown that the coupled system of plasma and dielectric waveguides is capable of generating exceptional points where their dispersion curves cross. By controlling the connection (distance) between the waveguides, it is possible to control the distribution of the electromagnetic field, both in the plasma and in the dielectric waveguides around the exceptional point. It is also shown that in the presence of dissipative losses in the plasma, the degree of heating of the plasma waveguide can be controlled by tuning the distribution and intensity of the exciting electromagnetic field in the coupled waveguide system, which gives a potential advantage among other methods of plasma heating. The results obtained in the work can be considered as an example of a new method of controlled plasma heating, which can be used to overcome the existing problems of controlled thermonuclear fusion. [ABSTRACT FROM AUTHOR]

Electron beams produced in RF linear accelerators will naturally be modulated at the RF frequency. Here we report measurements of the RF harmonic content of a 21.6 MeV electron beam coasting in air, as well as the RF harmonic content of x-rays produced from that electron beam, and the effects of these modulated electron and x-ray beams on several fast detection systems. The RF fundamental and its higher harmonics were found to be impressed onto the x-rays generated from the electron beam, and the response of an RF waveguide to passage of the modulated x-ray signal indicated that this harmonic content was also impressed onto the secondary electrons produced by the passage of the x-rays through the waveguide. An unexpected, interference-like effect was observed, which was particularly prominent in the case of the waveguide when struck by the modulated x-rays. The participation of secondary electrons produced by passage of the x-rays through the x-ray converter upstream of the waveguide was ruled out as a significant contributor to this effect. [ABSTRACT FROM AUTHOR]

We present results from two new techniques for the generation of meter-scale, low density (∼ 1 0 17 c m − 3 on axis) plasma waveguides, the "two-Bessel" technique, and the "self-waveguiding" technique. Plasma waveguides of this density and length range are needed for demonstration of a ∼10 GeV laser wakefield accelerator module, key for future staging for a ∼TeV lepton collider. Both techniques require the use of high quality ultrashort pulse Bessel beams to efficiently and uniformly ionize hydrogen gas in meter-scale supersonic gas jets via optical field ionization. We review these two techniques, describe our meter-scale gas jets, and present a new method for correction of optical aberrations in Bessel beams. Finally, we briefly present results from recent experiments employing one of our techniques, demonstrating quasi-monoenergetic acceleration of ∼5 GeV electron bunches in 20 cm long, low density plasma waveguides. [ABSTRACT FROM AUTHOR]

Electronic technologies, especially in the microwave and terahertz frequency ranges, including plasma show better interaction efficiency and higher output power as compared to apparatus with the vacuum. Also, in these frequency ranges, the plasma-filled high-power waveguides can support TE and TM modes. Therefore, in this study, the dispersion relation of electromagnetic (EM) waves in a new rippled-wall waveguide structure contain the plasma layer and coaxial dielectric geometry is numerically studied. The Maxwell equations and boundary conditions are employed to investigate and analyze the dispersion relation in TM mode for coaxial geometry dielectric rippled-wall waveguide contain the plasma layer. High-frequency radiations are observed from the proposed configuration. It is found that the frequency of the wave increases with a decrease in the corrugation amplitude and period. Moreover, a decrease in frequency is observed with an increase in dielectric radius and a decrease in plasma radius. [ABSTRACT FROM AUTHOR]

The feasibility of composite right/left-handed (CRLH) metamaterial waveguides based upon graphene plasmons is demonstrated via numerical simulation. Designs are presented that operate in the terahertz frequency range along with their various dimensions. Dispersion relations, radiative and free-carrier losses, and free-carrier based tunability are characterized. Finally, the radiative characteristics are evaluated, along with its feasibility for use as a leaky-wave antenna. While CRLH waveguides are feasible in the terahertz range, their ultimate utility will require precise nanofabrication, and excellent quality graphene to mitigate free-carrier losses. [ABSTRACT FROM AUTHOR]

Quasi-phase matching in corrugated plasma channels has been proposed as a way to overcome the dephasing limitation in laser wakefield accelerators. In this study, the phase-lock dynamics of a relatively long electron bunch injected in an axially-modulated plasma waveguide is investigated by performing particle simulations. The main objective here is to obtain a better understanding of how the transverse and longitudinal components of the wakefield as well as the initial properties of the beam affect its evolution and qualities. The results indicate that the modulation of the electron beam generates trains of electron microbunches. It is shown that increasing the initial energy of the electron beam leads to a reduction in its final energy spread and produces a more collimated electron bunch. For larger bunch diameters, the final emittance of the electron beam increases due to the stronger experienced transverse forces and the larger diameter itself. Increasing the laser power improves the maximum energy gain of the electron beam. However, the stronger generated focusing and defocusing fields degrade the collimation of the bunch. [ABSTRACT FROM AUTHOR]

We investigate the mode properties of planar dielectric aluminum-quinoline (Alq3) multilayer waveguides comprising one single or three equally spaced embedded nanometer-thin (~10 nm thick) Alq3-Mg0.9:Ag0.1 composite metal-island layers. The plasmonic waveguides were fabricated by organic molecular beam deposition. Transverse magnetic (TM) and transverse electric (TE) modes were selectively excited using the m-line method. The symmetric plasmonic TM0 mode was launched in all waveguides and—in addition—two higher order plasmonic TM1 and TM2 modes were generated in waveguides comprising three metal layers. Other TM modes have hybrid dielectric-plasmonic characters, showing an increased effective refractive index when one electric field antinode is close to a metallic layer. TM modes which have all their antinode(s) in the dielectric layers propagate essentially like dielectric modes. TE modes with antinode(s) at the position of the metal layer(s) are strongly damped while the losses are low for TE modes comprising a node at the position of the composite metal film(s). The possibility to control the effective refractive index and the losses for individual hybrid plasmonic-dielectric TM and dielectric TE modes opens new design opportunities for mode selective waveguides and TM-TE mode couplers. [ABSTRACT FROM AUTHOR]

We theoretically and numerically investigated the plasmon-induced transparency (PIT) effect in a single circular split-ring core ring resonator (CSRCRR) side coupled to a metal-isolator-metal waveguide, in which we can realize a single PIT effect window. The transmission line theory and the coupled mode theory are used. The results (transmission peak varies from 10% to 75%) show that the PIT window results from the destructive interference between the resonance modes in the CSRCRR. Then, the limit of wavelength detuning of the two modes in CSRCRR is studied. This work provides a new structure to realize the PIT effect and shows a new way to judge whether the phenomenon is the real PIT effect or not. [ABSTRACT FROM AUTHOR]

An analytical model of coaxial traveling-wave-tube-like waveguides with plasma filling has been justified and utilized to analyze the eigenmodes. Very often, introducing plasma into vacuum electronic devices leads to essential advantages as compared with evacuated tubes. The cylindrical structure under the present consideration consists of a central dielectric rod, placed inside a plasma coaxial layer with a metallic helix sheath on its outer interface, and a metal screen separated from the plasma by another dielectric layer. The dispersion properties of electromagnetic waves propagating across the external axial static magnetic field in such traveling-wave-tube-like waveguides are studied and summarized. The presence of a dense plasma coaxial layer makes the media nontransparent for waves in the electron cyclotron frequency range. However, surface type electromagnetic waves can propagate in this case. These waves are called azimuthal surface waves (ASWs). The helix sheath causes coupling of ordinarily and extraordinarily polarized ASWs. The zeroth radial ASW modes have been found to be most dangerous for parasitic wave excitation in dense plasma-loaded, coaxial traveling-wave-tube-like waveguides. [ABSTRACT FROM AUTHOR]

We measured the parameter reproducibility and radial electron density profile of capillary discharge waveguides with diameters of 650 $\mathrm{\mu} \mathrm{m}$ to 2 mm and lengths of 9 to 40 cm. To the best of the authors' knowledge, 40 cm is the longest discharge capillary plasma waveguide to date. This length is important for $\ge$ 10 GeV electron energy gain in a single laser-driven plasma wakefield acceleration stage. Evaluation of waveguide parameter variations showed that their focusing strength was stable and reproducible to $ % and their average on-axis plasma electron density to $ %. These variations explain only a small fraction of laser-driven plasma wakefield acceleration electron bunch variations observed in experiments to date. Measurements of laser pulse centroid oscillations revealed that the radial channel profile rises faster than parabolic and is in excellent agreement with magnetohydrodynamic simulation results. We show that the effects of non-parabolic contributions on Gaussian pulse propagation were negligible when the pulse was approximately matched to the channel. However, they affected pulse propagation for a non-matched configuration in which the waveguide was used as a plasma telescope to change the focused laser pulse spot size. [ABSTRACT FROM AUTHOR]

Whenever light is slowed down, for any cause, two different formulas give its momentum. The coexistence of those momenta was the heart of the century-old Abraham-Minkowski dilemma, recently resolved for dielectrics. We demonstrate that this framework extends to momentum exchange in wave-particle interaction; in particular to vacuum waveguides of electron tubes (dispersive metallic slow-wave structures). In waveguides, the dilemma can be easily investigated since energy and force are well established through the use of Maxwell equations in vacuum, and since waveguides can have a strong refractive index. Our theory is assessed with simulations validated against measurements from a traveling-wave tube. In addition, we show that the dilemma resolution is not limited to discriminating between kinematic and canonical momenta but also involves a non-negligible flowing momentum from Maxwell's electromagnetic stress. The existence of two momenta for diverse systems like materials, plasmas and waveguides, for which light velocity modification has entirely different origin, points to the universality of the Abraham-Minkowski dilemma. [ABSTRACT FROM AUTHOR]

A plasma channel created by the combination of a capillary discharge and inverse Bremsstrahlung laser heating enabled the generation of electron bunches with energy up to 7.8 GeV in a laser-driven plasma accelerator. The capillary discharge created an initial plasma channel and was used to tune the plasma temperature, which optimized laser heating. Although optimized colder initial plasma temperatures reduced the ionization degree, subsequent ionization from the heater pulse created a fully ionized plasma on-axis. The heater pulse duration was chosen to be longer than the hydrodynamic timescale of ≈ 1 ns, such that later temporal slices were more efficiently guided by the channel created by the front of the pulse. Simulations are presented which show that this thermal self-guiding of the heater pulse enabled channel formation over 20 cm. The post-heated channel had lower on-axis density and increased focusing strength compared to relying on the discharge alone, which allowed for guiding of relativistically intense laser pulses with a peak power of 0.85 PW and wakefield acceleration over 15 diffraction lengths. Electrons were injected into the wake in multiple buckets and times, leading to several electron bunches with different peak energies. To create single electron bunches with low energy spread, experiments using localized ionization injection inside a capillary discharge waveguide were performed. A single injected bunch with energy 1.6 GeV, charge 38 pC, divergence 1 mrad, and relative energy spread below 2% full-width half-maximum was produced in a 3.3 cm-long capillary discharge waveguide. This development shows promise for mitigation of energy spread and future high efficiency staged acceleration experiments. [ABSTRACT FROM AUTHOR]

Near the electrostatic plasma frequency, plasma exhibits a relative permittivity near zero, and this property has been used to make transient plasma waveguides at microwave and optical wavelengths by ionizing gases with pulsed electromagnetic fields and laser radiation. However, to our knowledge, no one has constructed a steady-state RF-excited plasma waveguide for the purpose of studying its microwave attenuation and dispersion characteristics. We report here the results of investigations at 2.8–3.7 GHz of a variable-length plasma waveguide up to 30 cm long in which the plasma's relative permittivity was as low as 0.2. De-embedded S-parameter power loss is as low as 4.6 dB and the dispersion is largely consistent with theory, although further work remains to be done. [ABSTRACT FROM AUTHOR]

An analog of an optical waveguide in the form of a chain of metallic nanoparticles has been investigated using modified cylindrical dielectric resonators in the microwave band. Similar to the plasma oscillations in spherical nanoparticles, the two lowest resonances of the dielectric resonator correspond to the dipole and quadrupole oscillatory modes. It is shown that a waveguide consisting of seven resonators exhibits high frequency selective properties and relatively low loss if the resonances of the quadrupole oscillatory modes are used to form its passband. The characteristics of the investigated waveguide remain almost unchanged at its bending by 90°, and the cross section of localization of the main part of the energy propagating in the waveguide is smaller than the electromagnetic wavelength by a factor of five, which approximately corresponds to the optical waveguides based on plasma oscillations in nanoparticles. [ABSTRACT FROM AUTHOR]

An optical switch based on liquid crystal dielectric loaded surface plasmon polariton waveguides is proposed and theoretically analyzed. The infiltration of the plasmonic structure with a nematic liquid crystalline material serving as the dielectric loading is shown to allow for extensive electrical tuning of its waveguiding characteristics. Both the electrical switching and optical properties of the proposed waveguide are investigated in the context of designing a directional coupler optical switch, which is found to combine efficient voltage control, low power consumption, high extinction ratio, and relatively low insertion losses. [ABSTRACT FROM AUTHOR]

This paper investigates theoretically and numerically local heating effects in plasmon nanofocusing structures with a particular focus on the sharp free-standing metal wedges. The developed model separates plasmon propagation in the wedge from the resultant heating effects. Therefore, this model is only applicable where the temperature increments in a nanofocusing structure are sufficiently small not to result in significant variations of the metal permittivity in the wedge. The problem is reduced to a one-dimensional heating model with a distributed heat source resulting from plasmon dissipation in the metal wedge. A simple heat conduction equation governing the local heating effects in a nanofocusing structure is derived and solved numerically for plasmonic pulses of different lengths and reasonable energies. Both the possibility of achieving substantial local temperature increments in the wedge (with a significant self-influence of the heating plasmonic pulses), and the possibility of relatively weak heating (to ensure the validity of the previously developed nanofocusing theory) are demonstrated and discussed, including the future applications of the obtained results. Applicability conditions for the developed model are also derived and discussed. [ABSTRACT FROM AUTHOR]

This work reports on the comparative studies of Raman enhancement in liquid core waveguides (LCWs). The theoretical considerations that describe Raman enhancement in LCWs is adapted to analyze and compare the performance of hollow core photonic crystal fibers (HCPCFs) to conventional Teflon capillary tubes. The optical losses in both platforms are measured and used to predict their performance for different lengths. The results show that for an optimal waveguide length, two orders of magnitude enhancement in the Raman signal can be achieved for aqueous solutions using HCPCFs. This length, however, cannot be achieved using normal capillary effects. By integrating the interface of the fluidic pump and the HCPCF into a microfluidic chip, we are able to control fluid transport and fill longer lengths of HCPCFs regardless of the viscosity of the sample. The long-term stability and reproducibility of Raman spectra attained through this platform are demonstrated for naphthalenethiol, which is a well-studied organic compound. Using the HCPCF platform, the detection limit of normal Raman scattering in the range of micro-molars has been achieved. In addition to the higher signal-to-noise ratio of the Raman signal from the HCPCF-platform, more Raman modes of naphthalenethiol are revealed using this platform. [ABSTRACT FROM AUTHOR]

We observed the parameters of the discharge-produced plasma in cylindrical capillary. Plasma parameters of the waveguide were investigated by use of both a Normarski laser interferometer and a hydrogen plasma line spectrum. A space-averaged maximum temperature of 3.3 eV with electron densities of the order of 1017 cm-3 was observed at a discharge time of 150 ns and a maximum discharge current of 200 A. One-dimensional dissipative magnetohydrodynamic (MHD) code was used to analyze the discharge dynamics in the gas-filled capillary discharge waveguide for high-intensity laser pulses. Simulations were performed for the conditions of the experiment. We compared the temporal behavior of the electron temperature and the radial electron density profiles, measured in the experiment with the results of the numerical simulations. They occurred to be in a good agreement. An ultrashort, intense laser pulse was guided by use of this plasma channel. [ABSTRACT FROM AUTHOR]

This article presents the analysis of the laser-produced-plasma (LPP) formed by the focusing of a 9 ns laser pulse, λ=532 nm, with a NA=0.6 aspherical lens using energies between 100-1500 μJ, into distilled water with varying solutions of table salt. Observations of the filamentation plasma were made, which are explained by self-focusing of the laser pulse by the LPP through ponderomotive cavitation of the electron plasma in the center of the beam. The filamentation of the beam through a low density plasma wave guide explains why the transmission of the pump laser through the interaction region was notably higher on previous experiments that we performed [R. Evans et al., Opt. Express 16, 7481 (2008)], than a very similar set of experiments performed by Noack and Vogel [IEEE J. Quantum Electron. 35, 1156 (1999)]. [ABSTRACT FROM AUTHOR]

Grain orientation is known to yield high thermal conductivity oriented yttrium silicon oxynitride (Y2O3-Si3N4). However, the anisotropic thermal conductivity of oriented Y2O3-Si3N4 in the stacking direction falls below that of nonoriented Y2O3-Si3N4 and Si3N4 at temperatures above 280 K and 630 K, respectively. Hence, it is unclear will grain orientation actually lead to better heat diffusions from the InGaAs/AlAsSb ultrafast all-optical cross-phase modulators or any other semiconductor devices to the oriented Y2O3-Si3N4 thin-film. To probe into this, the heat diffusion in an InGaAs/AlAsSb ultrafast all-optical cross-phase modulator whereby nonoriented and oriented Y2O3-Si3N4 thin-films are used as the heat-spreader is performed. Analysis shows that grain orientation in Y2O3-Si3N4 thin-film reduces the thermal resistance at the device-film interface through reduced void density, and leads to a marginally better heat diffusion in the device compared to nonoriented Y2O3-Si3N4 thin-film. Consequently, oriented Y2O3-Si3N4 thin-film heat-spreader improves the power-handling of the InGaAs/AlAsSb ultrafast all-optical cross-phase modulator by ∼0.46-∼1.8 times of the original value compared to ∼0.36-∼1.75 times of the original value for the case of nonoriented Y2O3-Si3N4 thin-film heat-spreader. [ABSTRACT FROM AUTHOR]

We report measurements of the nonlinear refractive index, n2, and the nonlinear absorption coefficient, α2, of Pb(PO3)2-WO3 glasses. The measurements were performed using 100 fs (17 ps) laser pulses at 800 nm (1064 nm). Positive values of n2∼10-19 m2/W and negligible α2 were measured. The results show that the nonlinearity is faster than 100 fs and it is observed an increase of n2 with the increasing of the WO3 amount in the samples. The Boling, Glass, and Owyoung model, based on the semiclassical harmonic oscillator model, was used to predict the values of n2, with basis on the values of the linear refractive index of the samples. [ABSTRACT FROM AUTHOR]

A detailed model of plasma dynamics, which self-consistently integrates plasma-kinetic, Navier–Stokes, electron heat conduction, and electron-vibration energy transfer equations, is used to quantify the limitations on the lifetime of microwave plasma waveguides induced in the atmosphere through filamentation with high-intensity ultrashort laser pulses further sustained by long laser pulses. We demonstrate that a near-infrared or midinfrared laser pulse can tailor plasma decay in the wake of a filament, efficiently suppressing, through electron temperature increase, the attachment of electrons to neutral species and dissociative recombination, thus substantially increasing the plasma-guide lifetime and facilitating long-distance transmission of microwaves. [ABSTRACT FROM AUTHOR]

Propagation of electromagnetic waves in planar waveguides made of metamaterials with negative values of the relative permittivity and relative permeability is analyzed. The specific features of radiation from antennas manufactured on the basis of planar metamaterial waveguides are studied. It is shown that radiation of such antennas is characterized by the backward radiation effect, i.e., the maximum of the radiation pattern is formed at 180°. The causes of this effect and the conditions for its appearance are revealed. It is proved that this effect appears only in the antennas manufactured on the basis of metamaterial waveguides with negative values of the relative permittivity and relative permeability. A design version of a scanning two-mode antenna operating on the basis of this effect is proposed. [ABSTRACT FROM AUTHOR]

The effect of intersubband (ISB) pump-wavelength detuning, spatial ISB absorption, and optical confinement on the characteristics of the ultrafast all-optical cross-phase modulation (XPM) in InGaAs/AlAs/AlAsSb coupled double-quantum-well (CDQW) ISB transition optical waveguides are studied. For pump energies below the saturation point of ISB absorption, experimental and theoretical results show that all the photons confined to the absorption layers are absorbed. Consequently, higher ISB absorption coefficients do not lead to improved XPM efficiency. Increasing ISB absorption may be effective in raising the saturation point of ISB absorption so that higher induced phase shift may be achieved at higher pump energies. Nevertheless, it is found that the pump energy of these devices should be limited to below approximately 10 pJ at the input facet of these devices. Otherwise, the effects of two-photon absorption become considerable and this leads to reduced throughput of these devices. Hence, it becomes apparent that the approach to enhance the XPM efficiency for any given absorption-layer volume of any CDQW design of these devices is to increase the optical confinement to the absorption layers. [ABSTRACT FROM AUTHOR]

The integration of two-dimensional III-V InP-based photonic crystal and silicon wire waveguides is achieved through an accurate alignment of the two optical levels using mix-and-match deep ultraviolet (DUV)/electron beam lithography. The adhesively bonded structures exhibit an enhancement of light emission at frequencies where low group velocity modes of the photonic crystal line defect waveguides occur. Pulsed laser operation is obtained from these modes at room temperature under optical pumping. The laser light is coupled out of the Si waveguide via grating couplers directly to single mode fiber. [ABSTRACT FROM AUTHOR]

A subwavelength grating waveguide (GW) consisting of two parallel metallic slabs with periodic corrugations on their inner boundaries is developed to slow down the speed of light at terahertz frequencies. Assisted by a tapered input port, our structure has a transfer efficiency of about 80% over a broad bandwidth and strong confinement in the subwavelength scale. Based on the GW, three graded GWs are designed to demonstrate that the spoof surface plasmon polaritons are slowed down and asymptotically stopped when they tend to the location, where the local cutoff frequency is the same as the frequency of the incident light. [ABSTRACT FROM AUTHOR]

The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth’s upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models. [ABSTRACT FROM AUTHOR]

We introduce a mapping from configuration interaction singles wavefunctions, expressed as linear combinations of particle-hole excitations between Hartree–Fock molecular orbitals, to real-space exciton wavefunctions, expressed as linear combinations of particle-hole excitations between localized Wannier functions. The exciton wavefunction is a two-dimensional amplitude for the exciton center-of-mass coordinate, R, and the electron-hole separation (or relative coordinate), r, having an exact analogy to one-dimensional hydrogenlike wavefunctions. We describe the excitons by their appropriate quantum numbers, namely, the principle quantum number, n, associated with r and the center-of-mass pseudomomentum quantum number, j, associated with R. In addition, for models with particle-hole symmetry, such as the Pariser–Parr–Pople model, we emphasize the connection between particle-hole symmetry and particle-hole parity. The method is applied to the study of excitons in trans-polyacetylene and poly(para-phenylene). [ABSTRACT FROM AUTHOR]

This paper studies the guided-wave transmission of terahertz electromagnetic waves along the surface waveguides and parallel-plate waveguides (PPWGs). Field analysis is presented to show that low-loss and quasi-TEM propagation is only possible when the waveguides are operating in their plasmonic modes. It is shown that the observed low-loss and quasi-TEM propagation of terahertz waves in the PPWGs is due to resonant coupling of surface plasmons between the two plates. Transmission line models based on the peculiar characteristics of the surface waves associated with the plasmonic modes of the guides are developed and the distinctions with the conventional transmission line theory are highlighted. [ABSTRACT FROM AUTHOR]

The effects of air gaps in metal stripe waveguides supporting long-range surface plasmon polaritons have been determined theoretically. The study is motivated by a recently adopted fabrication approach based on direct bonding, where various kinds of air gaps may form near the metal stripe due to fabrication imperfections. Specifically, “Air wings,” a top air gap, and side air gaps have been considered as possible perturbations. The main effects of the air gaps on the propagation of the long-range surface plasmon-polariton wave are that its attenuation and confinement decrease as the gaps become more invasive, and that its mode fields become strongly perturbed. Taken together, these effects are deleterious, so air gaps do not appear suitable for range extension. In general, very small air gaps can only be tolerated before confinement is completely lost. A lower-index planarizing layer could be used to help eliminate air gaps but the waveguide design space becomes constrained. The air gaps perturb the long-range mode such that its main transverse electric-field component (Ey) develops a maximum within the gaps and some localization therein. This feature could be interesting in applications where high-intensity fields in nanometric air gaps are sought, but only if coupling and radiation losses are not much of a concern. [ABSTRACT FROM AUTHOR]

The theoretical study on the electron beam-wave interactions in a plasma waveguide immersed in a finite magnetic field is given in the article, in which both the plasma and the electron beam are considered as special media. Making use of the constitutive transformation and the Lorentz transformation in the four-dimensional space, the permittivity tensor of the stationary magnetized plasma, the permittivity tensor, the permeability tensor, and the chiral tensor of the electron beam in the rest (laboratory) frame are acquired. Therefore, two coupled wave equations for the magnetized plasma and electron beam have been obtained and the dispersion relations are then achieved by solving these coupled equations together with the boundary conditions including the surface current density due to the ripple of the plasma/beam. As an example of the applications of this approach, the beam-wave interactions in a practical plasma Cherenkov maser have been studied and the numerical calculations have been carried out in detail. It has been found that the present approach is more accurate and can provide clearer mode information for the electron beam-wave interactions in a magnetized plasma waveguide. This approach can be exploited in a number of electron beam-wave interaction systems including some kinds of free electron devices, plasma filled Cherenkov radiated free electron lasers and masers. [ABSTRACT FROM AUTHOR]

We present an extended study of different topologies for lattice-deformed two-dimensional single line-defect (W1) photonic crystal channel waveguide bends and their effect on the optimization of the bend transmission properties. An enhancement of the spectral response by a factor of six was obtained, with the optimal design providing transmission greater than 95% over a 5.2% relative bandwidth. Experimental results for devices realized in III–V semiconductor epitaxial structure show a transmission efficiency of 95%. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We investigate, both experimentally and theoretically, the waveguiding properties of a double-trench waveguide in which a conventional single-mode strip waveguide is embedded in a two-dimensional photonic crystal (PhC) slab formed in silicon-on-insulator wafers. We demonstrate that the bandwidth for relatively low-loss (50 dB/cm) waveguiding is significantly expanded to 250 nm, covering almost all the photonic bandgap owing to nearly linear dispersion of the TE-like waveguiding mode. The flat transmission spectrum, however, is interrupted by numerous narrow stop bands. We found that these stop bands can be attributed to anticrossing between TE-like (positive parity) and TM-like (negative parity) modes. This effect is a direct result of the strong asymmetry of the waveguides that have an upper cladding of air and lower cladding of oxide. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Previously, we have described a low temperature grown GaAs device that uses single-photon absorption to perform a carrier lifetime limited optical autocorrelation of picosecond optical pulses. In this article, we describe how this same device could be used to perform an autocorrelation of femtosecond optical pulses by utilizing two-photon absorption (TPA). Furthermore, we propose how to model and minimize the photocurrent’s dependence on the single-photon absorption (SPA) response of the midlevel traps. We find that the SPA response produces a distortion on the TPA autocorrelation signal at low intensities. At large peak intensities (I[sub peak]≈3G W cm[sup -2]), however, we find that the SPA distortion becomes nearly two orders of magnitude smaller than the TPA signal, and decreases further with increasing intensity. In our discussion, we also describe some of the tradeoffs between using a photoconductor with a large two-photon absorption coefficient and midlevel states as a TPA autocorrelator. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report a surface-normal optically controlled waveguide switch made of a p-i-n diode that utilizes optically induced voltage screening to turn on and diffusive conduction to turn off. We examine theoretically diffusive conduction in these switches and show that this mechanism offers the possibility of creating optical switches operating at several tens of GHz. As a proof-of-concept demonstration, we present experimental results of wavelength-converting, optical switching at frequencies up to 2.5 GHz in a multiple-quantum-well, GaAs-based waveguide device using milliwatt-level switching powers. Optimized arrays of these devices can be used for high-speed, multichannel wavelength conversion and optical regeneration in wavelength-division-multiplexed systems. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polarization shift and temperature sensitivity are important issues in optical waveguides. Applying stresses is a promising method to control these optical parameters. In this article, analytical solutions are obtained to estimate the stress effects on these optical parameters. Because the refractive index variation induced by the stresses is very small, the linear approximation is used to obtain the closed-form solutions to estimate the stress induced effective index change in a slab waveguide. The solutions are, then, extended to estimate the stress induced effective index change, polarization shift, and the temperature sensitivity of a channel waveguide by use of effective index method. As an example, the optical parameters controlled by the thermal stresses, which are induced by attaching an Al plate on the bottom of the substrate, are analyzed. The results show that the polarization shift and the temperature sensitivity of the central wavelength can be tuned in a large range by varying the Al plate thickness and the curing temperature. The effects can be modified by changing the shape of the Al plate. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We develop a model to study coupled cavity waveguides (CCWs) in photonic crystals, composed of linear chains of coupled cavities. By extending previous work on single mode cavities, we have developed a model applicable to any finite number of quasi-degenerate cavity modes. Our model, which uses a multimode tight-binding approach, allows us to study the interaction between the cavity modes as well as the coupling between the CCW bands. In contrast to previous work the coupling parameters are calculated ab initio from the single cavity field profile. The calculated dispersion relations are shown to be in good agreement with those obtained from the plane wave expansion method. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Optical loss and polarization characteristics of the photonic crystal stick waveguide resonator modes were investigated using both theory and experiment. A stick waveguide resonator with 12 missing air holes was found to have a very high Q(>3 800 000) mode originating from the lossless guided mode below the light line. Photoluminescence spectra show sharp resonance peaks at regular intervals in k space, satisfying the resonant condition. Linear polarizations parallel or perpendicular to the waveguide were observed, depending on the mode symmetry. This polarization selection is explained in terms of the far-field cancellation effect of the in-plane field components. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A laser beam can be efficiently fed into a planar thin film by means of a prism–film coupler. The properties of the cavity modes, the coupling efficiency, the optimum coupling condition, etc. of the prism–film coupler can be explained using the theory developed by Tien and Ulrich [P. K. Tien and R. Ulrich, J. Opt. Soc. Am. 60, 1325 (1970)]. Based on multiple scattering and multiple wave interference, we propose a theory of the two modes referred to as the leaky and degenerate modes. The properties of the two kinds of modes, such as positions, linewidths, angular spectrum of the leaky mode, and the degenerate mode spectrum are studied in detail. This theory gives an excellent explanation of the underlying origin of light wave propagation in the prism–film coupler. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Two optimized methods for accurately measuring the 1.5 µm lifetime of Er[sup 3+] in LiNbO[sub 3] crystals and waveguides are proposed. The first method, suitable for measurement of bulk material, was suggested by forming an annealed proton exchanged sandwich structure and fluorescence was collected through an adjustable aperture. This excitation collection scheme was used to investigate bulk Er-doped LiNbO[sub 3] crystals with eight different Er[sup 3+] doping levels, three different crystal thicknesses, and three different cut orientations. The 1.5 µm lifetime was investigated in three configurations: with both a sandwich and an aperture, with a sandwich but without an aperture, and without not only a sandwich but also without an aperture. In addition, the effect of the aperture was also studied. The second method, suitable for a waveguide structure, was proposed on the basis of transversely gathering the fluorescence aided by an outcoupling fiber. It was optimized by comparing three different fluorescence collection schemes. Using this method, the lifetimes of some Ti: Er:LiNbO[sub 3] strip waveguides were measured. In addition, the effect of radiation trapping on the polarized fluorescence spectrum was also investigated. The experimental results are discussed and summarized. [ABSTRACT FROM AUTHOR]

We investigate the transmission of ultrashort pulses through impurity band-based photonic crystal waveguides. It is found that in the general case the transmission behavior depends strongly on the pulse width with respect to the resonance linewidth in impurity bands. By controlling the configuration of the waveguides, quasiflat impurity bands can be obtained in which the dependence of transmission on pulse width is very weak. As long as the pulse width is much narrower than the bandwidth, pulses can transmit through the quasiflat impurity bands with negligible distortion and attenuation. The conditions necessary for achieving quasiflat impurity bands are derived by examining waveguides of different configurations and properties. The mechanism responsible for the formation of quasiflat impurity bands is revealed from the discussion of the symmetry of single defect and their coupling. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have used a rate equation propagation model of an Er[sup 3+]/Yb[sup 3+] doped Al[sub 2]O[sub 3] waveguide amplifier with copropagating pump at 980 nm to investigate the dependence of gain on Yb[sup 3+] concentration. The model includes excited state absorption and energy transfer upconversion processes within the Er[sup 3+] as well as the relevant energy transfer processes between Yb[sup 3+] and Er[sup 3+]. The results of the calculations indicate a close relationship of the parameters gain, launched pump power, waveguide length, and Yb[sup 3+] concentration. Codoping with a well-chosen Yb[sup 3+] concentration is shown to increase the gain around 1530 nm for all combinations of these parameters. The gain is improved most by Yb[sup 3+] codoping at pump powers around the amplifier threshold. At high pump powers the increase in gain of an Er[sup 3+]/Yb[sup 3+] doped waveguide is insignificant compared to that of its Er[sup 3+] doped counterpart. Furthermore for each launched pump power, a nonzero Yb[sup 3+] concentration can be determined, which maximizes the gain. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Properties of transverse electric waves in the microwave frequency range on a plane interface between a nonlinear antiferromagnet and a linear ferromagnet are investigated. It is revealed that there are two different field distributions and powers. An exact analytical dispersion relation is obtained. On the basis of the dispersion relation, we have investigated the properties of surface waves in this waveguide and, theoretically, found that there exist passbands and stop bands, which can be controlled by varying the power in the nonlinear gyromagnetic waveguides. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]