Ultraslow surface plasmons in metamaterial waveguides

A modified planar waveguide made of a metamaterial with negative permittivity and permeability has been considered. The modification of the waveguide by the introduction of an air channel qualitatively changes its dispersion characteristics due to the appearance of an ultraslow mode. The fields and properties of this mode have been investigated. The mode has been shown to be similar to a surface plasmon. In addition, it has been shown that the plasmons can propagate in subwavelength waveguides. Such ultraslow plasmons can be used in plasmonics and microwave and accelerator techniques.     

Low-loss silica-on-silicon waveguides

Waveguiding structures are one of the fundamental components of integrated photonic circuitry. Devices with low loss and a linear response across a wide wavelength range are especially desirable. In the present Letter, we have successfully developed and characterized low-loss silica waveguides integrated on a silicon substrate with a novel suspended cylinder geometry. The unique design creates a device that is effectively air clad, resulting in a large refractive index contrast for improved optical field confinement. The measured loss is constant from 658 to 1550 nm, and it is independent of the polarization of the input light and the input power.     

Numerical modelling of TE and TM modes in lossy nonlinear optical waveguides

The intensity-dependent characteristics of nonlinear TE and TM waves in a thin film bounded by lossy nonlinear media are analysed by the finite-element method. In this approach, the power-dependent complex propagation constants and local complex electromagnetic field distributions of lossy nonlinear TE and TM waves are obtained directly from the given lossy nonlinear waveguides, without any approximations. Numerical results for these modes in a lossy nonlinear waveguiding system with different absorption coefficients are given. It is shown that the complex dispersion relations, for both TE and TM modes, are strongly power dependent.     

Ultraslow surface plasmons in metamaterial waveguides for subwavelength resolution

A modified planar waveguide made of a metamaterial with negative permittivity and permeability has been considered. The modification of the waveguide by the introduction of an air channel qualitatively changes its dispersion characteristics due to the appearance of an ultraslow mode. The fields and properties of this mode have been investigated. The mode has been shown to be similar to a surface plasmon. In addition, it has been shown that the plasmons can propagate in subwavelength waveguides. Such ultraslow plasmons can be used in plasmonics, microwave and accelerator techniques.     

Transverse electromagnetic modes in aperture waveguides containing a metamaterial with extreme anisotropy

We use metamaterials with extreme anisotropy to solve the fundamental problem of light transport in deep subwavelength apertures. By filling a simply connected aperture with an anisotropic medium, we decouple the cutoff frequency and the group velocity of modes inside apertures. In the limit of extreme anisotropy, all modes become purely transverse electromagnetic modes, free from geometrical dispersion, propagate with a velocity controlled by the transverse permittivity and permeability, and have zero cutoff frequency. We analyze physically realizable cases for a circular aperture and show a metamaterial design using existing materials.     

TE modes in parallel cylindrical surface waveguides

Dispersion equations for TE and TM modes in width-limited waveguides formed by parallel cylindrical surfaces are derived in adiabatic approximation. It is shown that the dominant TE₀₁ mode is strongly localized in the waveguide center.     

Low-loss negative-index metamaterial at telecommunication wavelengths

We fabricate and characterize a low-loss silver-based negative-index metamaterial based on the design of a recent theoretical proposal. Comparing the measured transmittance and reflectance spectra with theory reveals good agreement. We retrieve a real part of the refractive index of Re(n)= -2 around 1.5 microm wavelength. The maximum of the ratio of the real to the imaginary part of the refractive index is about three at a spectral position where Re(n)= -1. To the best of our knowledge, this is the best figure of merit reported for any negative-index photonic metamaterial to date.     

Low-loss multimode waveguides crossings and turning mirrors

We develop a new design that the perturbation is the minimum when the crossing occurs at the self- image location in a low-loss multimode waveguide. We use a center-fold low-loss multimode waveguide with a single self image at the center. Such waveguides can cross at 90 degrees or 60 degrees at the center with minimal cross talk. One can reflect the incident mode into an intersecting waveguide by introducing an idea reflecting plane. In practice, the reflector is replaced by a plane for total internal reflection with correction for Goos-Hanchen shift.     

On the classification of discrete modes in lossy planar waveguides: the modal analysis revisited

In integrated-optical components such as integrated optical detectors or semiconductor light amplifiers, multilayer dielectric waveguiding structures occur in which some layers may be strongly lossy or may have gain. In such structures, the classification of the guided modes may become impossible. This paper reviews the modal analysis in which modes are only considered in connection with their possible excitation with a current line-source. Starting from the lossless situation, the analysis is extended to the lossy case and the details of the classification problem are investigated numerically. It was found that the validity of a unique classification is always limited. For that reason it is investigated, whether the classification problem might be due to the fact that in the time-harmonic formulation, the physical requirement of causality has been lost. To test this hypothesis, wave propagation is investigated along lossy waveguides in the timeLaplace-transform domain and using Lerch's causality theorem. It surprisingly turns out that in the time-Laplace-transform domain, the discrete part of the longitudinal spectrum does not exist, so that the test of the hypothesis is not conclusive. The classification problem of guided modes in strongly lossy waveguides is still an open problem. This revised version was published online in November 2006 with corrections to the Cover Date.     

Temporal solitons in magnetooptic and metamaterial waveguides

The important topic of temporal soliton propagation in double-negative metamaterials is discussed with an emphasis upon short pulses that exhibit self-steepening controlled by the frequency dependence of the relative permittivity and permeability. In addition, magnetooptic control is included, leading to some fascinating outcomes that should have practical application. The role of self-steepening, Raman scattering, third-order dispersion and magnetooptics is thoroughly investigated, and it is shown that pulses can acquire signatures in the form of additional velocities with respect to the moving frame. The metamaterial influence upon self-steepening has such a strong frequency dependence that it can be used to combat Raman scattering. The self-steepening can change sign, and it is shown that it is possible to arrange pulses in special switching formats to organise the output times. The metamaterial influence upon bit-patterns admits an important degree of control over multi-pulse interactions, and this is combined with magnetooptics to restore patterns. The role of third-order dispersion is also presented. Again, a control of the pulse behaviour in the neighbourhood where the frequency dependence causes the group-velocity dispersion parameter to approach zero is a direct consequence of using this kind of metamaterial. Finally, a Lagrangian analysis is used to support simulations of the positions of the pulse maxima.     

Low-loss submicrometer silicon-on-insulator rib waveguides and corner mirrors

Rib microwaveguides are demonstrated on silicon-on-insulator substrates with Si film thickness of either 380 or 200 nm and a width of 1 microm. Corner mirrors that allow compact 90 degrees turns between two perpendicular waveguides are characterized. Measured propagation losses are approximately 0.4 dB/cm and approximately 0.5 dB/cm for 380-nm and 200-nm Si film, respectively, and mirror losses are approximately 1 dB. This allows the development of applications such as optical interconnects in integrated circuits over propagation distances larger than several centimeters.     

Microwave response of octagon-shaped parallel plates: Low-loss metamaterial

A very low-loss metamaterial formed by a pair of homogeneous octagon-shaped parallel plates separated by a dielectric substrate is presented to achieve simultaneous negative permittivity and permeability in the microwave region. The double-negative behavior with a high figure of merit (FOM=|Re(n)/Im(n)|=80 at 24.7 GHz) leads to reduced losses in this proposed metamaterial. The high quality feature of the structure can make the applications of the negative refractive index metamaterial more efficient and applicable, such as perfect- or super-lenses at microwave frequencies since FOM≈64.5, where the real part of the refractive index ≈?1 at 25.3 GHz.     

Low-loss and highly polarized emission from planar polymer waveguides

The waveguiding properties and amplified spontaneous emission (ASE) of a blend of light-emitting gain-conjugated polymers were investigated. ASE-induced line narrowing occurs for excitation fluences larger than 100 microJ cm(-2), with a maximum optical-gain coefficient of 8 cm(-1). Energy transfer between the host and guest polymers, significantly reducing the self-absorption, leads to a loss coefficient of the waveguide as low as 0.3 cm(-1), which is believed to be the lowest value reported for active organic gain slabs and a highly polarized emission, with a polarization contrast up to 0.65. These results indicate that gain-conjugated polymer blends are state-of-the-art organic materials for lasing devices.     

Low-loss, low-cross-talk crossings for silicon-on-insulator nanophotonic waveguides

We present compact crossings for silicon-on-insulator photonic wires. The waveguides are broadened using a 3 microm parabolic taper in each arm. By locally applying a lower index contrast using a double-etch technique, loss of confinement is reduced and 97.5% transmission (-1.7 dB) is achieved with only -40 dB cross talk.     

Trapping of electromagnetic wave in single-negative metamaterial waveguides

We study the trapping properties of transverse magnetic (TM) waves in single-negative metamaterial waveguides including epsilon-negative (ENG) metamaterial and mu-negative (MNG) metamaterial. The relationship between effective refractive index and reduced core width is analyzed when the permittivities of ENG and MNG metamaterials are different, and the inflection on this curve can be regarded as the trapping point. Simulation results show that the properties in an ENG–MNG–ENG metamaterial waveguide are contrary to that in a MNG–ENG–MNG metamaterial waveguide. The sensitivity of trapping point to the change of permittivity makes the single-negative metamaterial waveguides to be an effective method to detect the permittivity variation and can be used as a new kind of waveguide sensor.     

Low-loss germanium strip waveguides on silicon for the mid-infrared

Mid-infrared photonics in silicon needs low-loss integrated waveguides. While monocrystalline germanium waveguides on silicon have been proposed, experimental realization has not been reported. Here we demonstrate a germanium strip waveguide on a silicon substrate. It is designed for single mode transmission of light in transverse magnetic (TM) polarization generated from quantum cascade lasers at a wavelength of 5.8 μm. The propagation losses were measured with the Fabry-Perot resonance method. The lowest achieved propagation loss is 2.5 dB/cm, while the bending loss is measured to be 0.12 dB for a 90° bend with a radius of 115 μm.     

Low-loss chalcogenide waveguides on lithium niobate for the mid-infrared

We demonstrate low-loss chalcogenide (As(2)S(3)) waveguides on a LiNbO(3) substrate for the mid-IR wavelength (4.8 μm). Designed for single-mode propagation, they are fabricated through photolithography and dry-etching technology and characterized on a mid-IR measurement setup with a quantum cascade laser. For straight waveguides, propagation loss as low as 0.33 dB/cm is measured and low-loss bends on the order of 100 μm are simulated, with measurement results showing <3 dB for a 250 μm bend radius. The coupling efficiency is estimated to be 81%. In addition, the influences of variations in width and bend radius are also investigated.     

Bisection algorithm to calculate hybrid modes of birefringent planar graded index waveguides

Guided modes of a planar dielectric waveguide which encounter a nondiagonal permittivity tensor are neither TE nor TM, but hybrid. They are described by a pair of coupled second-order differential equations for the transversal electric and magnetic field components. We construct a real-valued function which plays the role of the transversal electric or magnetic field in the uncoupled Sturm-Liouville differential equation for TE or TM modes. The number of zeroes, or nodes, of this function labels the modes. The nodes increase with the prospective propagation constant. This fact is proven by constructing suitable self-adjoint operators and referring to the minimax principle. The nodal properties allow to formulate an efficient bisection algorithm for effective indices and field distributions of guided hybrid modes.     

Analysis of third and one-third harmonic generation in lossy waveguides

A comprehensive study on the requirements for the highly efficient third harmonic generation(THG) and its inverse process, one-third harmonic generation(OTHG), in lossy waveguides is proposed. The field intensity restrictions for both THG and OTHG caused by loss are demonstrated. The effective relative phase ranges, supporting the positive growth of signal fields of THG and OTHG are shrunken by the loss. Furthermore, it turns out that the effective relative phase ranges depend on the intensities of the interacting fields. At last, a modified definition of coherent length in loss situation, which evaluates the phase matching degree more precisely, is proposed by incorporating the shrunken relative phase range and the nonlinear phase mismatch. These theoretical analysis are valuable for guiding the experimental designs for highly efficient THG and OTHG.