Showing papers on "Radiation mode published in 2007"

Implications of higher-order mode content in large mode area fibers with good beam quality.

Abstract: The impact of Higher-Order Mode content on beam quality in large mode area fibers supporting several guided modes is carefully investigated. It is shown that even excellent beam quality (M2 < 1.1) in LMA fibers does not guarantee low HOM content, and that the presence of HOMs can lead to significant uncontrollable changes in beam quality, peak intensity, and pointing uncertainty that depend on the uncontrollable relative phase of the modes in the fiber.

Metal–Dielectric Slot-Waveguide Structures for the Propagation of Surface Plasmon Polaritons at 1.55 $\mu{\hbox {m}}$

Abstract: We present a deep-subwavelength-size metal slot-waveguide structure which can efficiently propagate surface plasmon polaritons (SPPs) at 1.55 mum within a high-index material. Through a systematic design analysis, we investigate the intrinsic tradeoffs and suggest solutions to substantially increase the propagation length of SPPs combining high-index dielectrics and metal structures. By studying several metal/dielectric geometries, we have found that the slot-waveguide size can be significantly decreased by the use of high-index materials without compromising the overall propagation losses. Our analysis also indicates that the device size-scaling is ultimately limited by a cutoff thickness for the metal film in which the slot is defined. For film thicknesses below cutoff, radiation modes exist which leak out of the guiding region. For certain operating frequencies, the radiant energy leaks out into both free space modes as well as surface plasmons guided along the top/bottom metal surfaces of the device. We have shown that, by using a silicon filling, the cutoff thickness of a 100-nm-wide slot waveguide can be as small as 90 nm, compared with 750 nm for the unfilled reference structures. In addition, we have demonstrated that by the use of SiO2 gap regions surrounding the Si dielectric core in a 200times400-nm silver slot region (partially filled metal slot), we can considerably reduce the overall propagation losses to less than 0.14 dB/mum, corresponding to a propagation length of approximately 50 mum

Gain-guided, index-antiguided fiber lasers

Abstract: Optical fibers with large diameter cores having a negative index step from cladding to core combined with an adequately large gain coefficient in the core provide near-optimal mode properties for fiber lasers delivering robust single transverse mode operation with very large mode areas. Basic properties and simple design formulas for such fibers are presented.

Mode scalability in bent optical fibers

Abstract: This paper introduces a simple, analytical method for generalizing the behavior of bent, weakly-guided fibers and waveguides. It begins with a comprehensive study of the modes of the bent step-index fiber, which is later extended to encompass a wide range of more complicated waveguide geometries. The analysis is based on the introduction of a scaling parameter, analogous to the V-number for straight step-index fibers, for the bend radius. When this parameter remains constant, waveguides of different bend radii, numerical apertures and wavelengths will all propagate identical mode field distributions, except scaled in size. This allows the behavior of individual waveguides to be broadly extended, and is especially useful for generalizing the results of numerical simulations. The technique is applied to the bent step-index fiber in this paper to arrive at simple analytical formulae for the propagation constant and mode area, which are valid well beyond the transition to whispering-gallery modes. Animations illustrating mode deformation with respect to bending and curves describing polarization decoupling are also presented, which encompass the entire family of weakly-guided, step-index fibers.

Surface-emitting fiber laser

Abstract: In one aspect, the disclosure features an article, including a fiber waveguide extending along a waveguide axis, the fiber waveguide including a core extending along the waveguide axis and a confinement region surrounding the core. The confinement region is configured to guide radiation at a first wavelength, λ1, along the waveguide axis and is configured to transmit at least some of the radiation at a second wavelength, λ2, incident on the confinement region along a path, where λ1 and λ2 are different. The core includes a core material selected to interact with radiation at λ1 to produce radiation at λ2.

Scattering of surface plasmon polaritons at abrupt surface interfaces: Implications for nanoscale cavities

Abstract: We have developed a rigorous mode matching approach for the exact semi-analytical analysis of surface plasmon propagation across non-uniform semi-infinite dielectric-metal interfaces. We address two key deficiencies of related approaches in the literature: firstly, we resolve issues of accuracy and convergence and secondly, while we focus on the analysis of two-dimensional problems, we present a framework for three-dimensional problems for the first time. Analytical derivations of coupling coefficients between guided and radiation modes allow an efficient scattering matrix formulation to describe general structures with multiple discontinuities. Studies of the reflection, transmission and radiation of surface plasmons incident on both dielectric and metallic surface discontinuities show a correspondence with an effective Fresnel description. We also model a surface plasmon Distributed Bragg Reflector (DBR) capable of reflecting between 80% and 90% of incident surface plasmon power. Radiation mode scattering ultimately limits the DBR’s reflection performance rather than the intrinsic absorption of the metal. Thus alternative plasmonic geometries that suppress radiation modes, such as gap and channel structures, could be superior for the design of strongly reflective DBRs for integration in high Q-factor nano-scale cavities. We anticipate that this method will be an invaluable tool for the efficient and intuitive design of plasmonic devices based on structural non-uniformities.

Coupling between long range surface plasmon polariton mode and dielectric waveguide mode

Abstract: Coupling of TM mode between long range surface plasmon polariton (LRSPP) mode and conventional dielectric waveguide mode is demonstrated numerically with finite element method. The characteristics of a hybrid coupler, which consists of the LRSPP waveguide and conventional single mode dielectric waveguide, are analyzed. The high efficient coupling shows a possible route for integrating the SPP device and conventional dielectric optical devices together and a method to excite LRSPP mode with dielectric waveguide. Because the coupling just occurs on TM mode, this kind of the hybrid coupler can be used as polarization mode splitter and combiner.

Waveguides for performing enzymatic reactions

Abstract: The present invention is directed to a method and an apparatus for analysis of an analyte. The method involves providing a zero-mode waveguide which includes a cladding surrounding a core where the cladding is configured to preclude propagation of electromagnetic energy of a frequency less than a cutoff frequency longitudinally through the core of the zero-mode waveguide. The analyte is positioned in the core of the zero-mode waveguide and is then subjected, in the core of the zero-mode wave guide, to activating electromagnetic radiation of a frequency less than the cut-off frequency under conditions effective to permit analysis of the analyte in an effective observation volume which is more compact than if the analysis were carried out in the absence of the zero-mode waveguide.

Fabrication-tolerant waveguides and resonators

Abstract: An optical waveguide having a core region with a substantially rectangular cross-section with a selected aspect ratio of width to height. Embodiments include devices incorporating the optical waveguide and methods for using the optical waveguide.

Anti-resonant reflecting optical waveguide for imager light pipe

Abstract: An anti-resonant reflecting optical waveguide structure for reducing optical crosstalk in an image sensor and method of forming the same. The method includes forming a trench within a plurality of material layers and over a photo-conversion device. The trench is vertically aligned with the photo-conversion device and is filled with materials of varying refractive indices to form an anti-resonant reflecting optical waveguide structure. The anti-resonant reflecting optical waveguide structure has a core and at least two cladding structures. The cladding structure in contact with the core has a refractive index that is higher than the refractive index of the core and the refractive index of the other cladding structure. The cladding structures act as Fabry-Perot cavities for light propagating in the transverse direction, such that light entering the anti-resonant reflecting optical waveguide structure remains confined to the core. This reduces the chance of photons impinging upon neighboring photo-conversion devices.

Analysis of Piezoelectric Ultrasonic Transducers Attached to Waveguides Using Waveguide Finite Elements

Abstract: A finite-element modeling procedure for computing the frequency response of piezoelectric transducers attached to infinite constant cross-section waveguides, as encountered in guided wave ultrasonic inspection, is presented. Two-dimensional waveguide finite elements are used to model the waveguide. Conventional three-dimensional finite elements are used to model the piezoelectric transducer. The harmonic forced response of the waveguide is used to obtain a dynamic stiffness matrix (complex and frequency dependent), which represents the waveguide in the transducer model. The electrical and mechanical frequency response of the transducer, attached to the waveguide, can then be computed. The forces applied to the waveguide are calculated and are used to determine the amplitude of each mode excited in the waveguide. The method is highly efficient compared to time integration of a conventional finite- element model of a length of waveguide. In addition, the method provides information about each mode that is excited in the waveguide. The method is demonstrated by modeling a sandwich piezoelectric transducer exciting a waveguide of rectangular cross section, although it could be applied to more complex situations. It is expected that the modeling method will be useful during the optimization of piezoelectric transducers for exciting specific wave propagation modes in waveguides.

Interface device for performing mode transformation in optical waveguides

Abstract: An interface device for performing mode transformation in optical waveguides includes an optical waveguide core for propagating light of a particular wavelength or a plurality of wavelengths. The optical waveguide core terminates in a subwavelength grating configured to change the propagation mode of the light. The subwavelength grating has a pitch sufficiently less than the wavelength of the light to frustrate diffraction. The device can thus serve as an optical coupler between different propagating media, or as an anti-reflective or high reflectivity device.

High Q, one-dimensional terahertz photonic waveguides

Abstract: A one-dimensional (1D) photonic metal parallel plate waveguide is presented in the spectral range of 0.5–3THz that has high throughput and stop bands with up to the experimental limit of 40dB of dynamic range. By incorporating a defect into the periodic bottom plate of the waveguide, a transmission resonance is generated in the first stop band with a Q value of 120 and a dynamic range of over 17dB. The 1D geometry allows the utilization of the mode matching technique to analytically calculate the transmission of the photonic waveguide.

Electrically pumped semiconductor evanescent laser

Abstract: An apparatus and method electrically pumping a hybrid evanescent laser. For one example, an apparatus includes an optical waveguide disposed in silicon. An active semiconductor material is disposed over the optical waveguide defining an evanescent coupling interface between the optical waveguide and the active semiconductor material such that an optical mode to be guided by the optical waveguide overlaps both the optical waveguide and the active semiconductor material. A current injection path is defined through the active semiconductor material and at least partially overlapping the optical mode such that light is generated in response to electrical pumping of the active semiconductor material in response to current injection along the current injection path at least partially overlapping the optical mode.

Single-mode single-polarization holey fiber using anisotropic fundamental space-filling mode

Abstract: We present the single-mode single-polarization regime of a circular-hole holey fiber consisting of a core with large elliptical holes. The elliptical holes in the core, which produce large anisotropies, split the fundamental mode into two orthogonally polarized fundamental modes, often referred to as slow and fast modes. This fiber can guide only one polarization state of the fundamental mode when a fundamental space-filling mode index of the cladding region is designed to lie between these indices of the slow and fast modes of the core region. We demonstrate one design example of this fiber and show that the single-polarization regime can be achieved over a wide wavelength range.

Plasmon excitation by the gaussian-like core mode of a photonic crystal waveguide

Abstract: A sensor and method for surface plasmon resonance sensing, wherein a small variation of the refractive index of an ambient medium results in a large variation of loss of a sensing mode. The surface plasmon resonance sensor comprises an antiguiding waveguide including a core characterized by a refractive index and a reflector surrounding the core. The reflector has an external surface and is characterized by a band gap and a refractive index higher than the refractive index of the core. A coating is deposited on the external surface of the core, the coating defining with the ambient medium a coating/ambient medium interface. In operation, the coating is in contact with the ambient medium, and the antiguiding waveguide is supplied with an electromagnetic radiation to (a) propagate a mode for sensing having an effective refractive index lower than the refractive index of the core and higher than a refractive index of an ambient medium and (b) produce surface plasmons at the coating/ambient medium interface. The mode for sensing is phase-matched with the surface plasmons at a wavelength within the band gap and a variation of the refractive index of the ambient medium results in a variation of loss of the sensing mode to detect a characteristic of the ambient medium.

Polarization rotator and method for manufacturing the same

Abstract: An optical circuit comprises: a first waveguide; a second waveguide: and a third waveguide that converts mode field and direction of polarization of light of said first waveguide at the same time to perform wave guiding to said second waveguide: wherein large aspect ratio directions of corresponding ends of a core of said first waveguide and a core of said second waveguide differ from each other.

Low bend loss quasi-single-mode optical fiber and optical fiber line

Abstract: Quasi-single mode optical waveguide fibers are disclosed that are bend resistant and capable of providing single mode transmission, for example at wavelengths greater than 1260 nm when the fundamental mode of optical energy is launched into the core of the fiber. Optical fiber line incorporating quasi-single mode optical waveguide fiber is also disclosed. Jumpers, or patchcords, utilizing quasi-single mode optical waveguide fiber are also disclosed herein. The fibre index profile consists of a double core (20,30) with an additional low index trench (50) for reducing bending losses.

Efficient and spurious-free integral-equation-based optical waveguide mode solver.

Abstract: Modal analysis of waveguides and resonators by integral-equation formulations can be hindered by the existence of spurious solutions. In this paper, spurious solutions are shown to be eliminated by introduction of a Rayleigh-quotient based matrix singularity measure. Once the spurious solutions are eliminated, the true modes may be determined efficiently and reliably, even in the presence of degeneracy, by an adaptive search algorithm. Analysis examples that demonstrate the efficacy of the method include an elliptical dielectric waveguide, two unequal touching dielectric cylinders, a plasmonic waveguide, and a realistic micro-structured optical fiber. A freely downloadable version of an optical waveguide mode solver based on this article is available.

1.54-μm TM-mode waveguide optical isolator based on the nonreciprocal-loss phenomenon: device design to reduce insertion loss

Abstract: We developed a 1.5-microm band TM-mode waveguide optical isolator that makes use of the nonreciprocal-loss phenomenon. The device was designed to operate in a single mode and consists of an InGaAlAs/InP ridge-waveguide optical amplifier covered with a ferromagnetic MnAs layer. The combination of the optical waveguide and the magnetized ferromagnetic metal layer produces a magneto-optic effect called the nonreciprocal-loss phenomenon--a phenomenon in which the propagation loss of light is larger in backward propagation than it is in forward propagation. We propose the guiding design principle for the structure of the device and determine the optimized structure with the aid of electromagnetic simulation using the finite-difference method. On the basis of the results, we fabricated a prototype device and evaluated its operation. The device showed an isolation ratio of 7.2 dB/mm at a wavelength from 1.53 to 1.55 microm. Our waveguide isolator can be monolithically integrated with other waveguide-based optical devices on an InP substrate.

Integrated lateral mode converter

Abstract: The invention describes method and apparatus for a mode converter enabling an adiabatic transfer of a higher order mode into a lower order optical mode within a photonic integrated circuit exploiting integrated semiconductor ridge waveguide techniques. As disclosed by the invention, such a mode conversion is achievable by using an asymmetric coupler methodology. In an exemplary embodiment of the invention, the invention is used to provide a low insertion loss optical connection between laterally-coupled DFB laser operating in first order mode and passive waveguide operating in the zero order optical mode. The integrated arrangement fabricated by using one-step epitaxial growth allows for a launch of the laser's light into the waveguide circuitry operating in the zero order lateral mode or efficiently coupling it to single-mode fiber, an otherwise high loss interface due to the difference in laser and optical fiber modes.

Millimeter waveband transceiver, radar and vehicle using the same

Abstract: In a millimeter waveband transceiver using an antenna and a waveguide for a connection line, it is necessary to perform transmission mode line conversion between TEM waves of a microstrip line and VTE01 mode waves of the waveguide. There is a limit to reducing the conversion loss using only a matching box for connecting the microstrip line with the waveguide. In a transmission mode line transducer for converting between the TEM waves of the microstrip line and the VTE01 mode waves of the waveguide, if the cross-sections are substantially the same size, in the case of a 50Ω microstrip line when the characteristic impedance of the waveguide is about 80%, i.e., 40Ω, the line conversion loss can be optimized. Therefore, the microstrip line is connected with the waveguide using a λ/4 matching box via a ridged waveguide having a low impedance and a length of λ/16 or less.

Plasmon mode transformation in modulated-index metal-dielectric slot waveguides.

Abstract: The concept of adiabatic mode transformation between silicon waveguide and surface plasmon-polariton modes in subwavelength metal-dielectric slots is investigated. The mode transformer consists of a modulated-index slot region, which is bound by two metal slabs. Using the design scheme, we will show that the optical dispersion of a modulated-index metal slot waveguide can be engineered well above the silicon light-line on a large wavelength region, allowing direct phase-matching between surface plasmon polaritons and traditional waveguide modes. Based on full-field, finite difference simulations, we demonstrate that reversible mode conversion can be achieved within submicrometer length scales.

Adaptive Wave Field Synthesis for Sound Field Reproduction: Theory, Experiments, and Future Perspectives

Abstract: Wave field synthesis (WFS) is a sound field reproduction technology that assumes that the reproduction environment is anechoic. A real reproduction space thus reduces the objective accuracy of WFS. Adaptive wave field synthesis (AWFS) is defined as a combination of WFS and active compensation. With AWFS the reproduction errors are minimized along with a departure penalty from the WFS solution. Analysis based on the singular value decomposition connects WFS, active compensation, and Ambisonics. The decomposition allows the practical implementation of AWFS based on independent radiation mode control. Results of experiments in different rooms support the theoretical propositions and show the efficiency of AWFS for sound field reproduction.

Excitation of a single hollow waveguide mode using inhomogeneous anisotropic subwavelength structures

Abstract: We propose and analyze a general approach for coupling a free space uniformly polarized beam to a desired hollow waveguide mode, thus enabling a single mode operation. The required spatial polarization state manipulation is achieved by use of inhomogeneous anisotropic subwavelength structures. Demonstration is obtained by coupling a linearly polarized CO2 laser beam at a wavelength of 10.6μm to the TE01, TM01, EH11, EH21, and EH31 modes of a 300μm diameter dielectric-coated hollow metallic waveguide. Full polarization and intensity analysis of the beam at the waveguide’s inlet and outlet ports indicates a high coupling efficiency to a single waveguide mode. Finally, shaping the waveguide mode to a nearly diffraction limited linearly polarized beam and to a radially polarized vectorial vortex are also demonstrated.

Surface plasmon mode analysis of nanoscale metallic rectangular waveguide.

Abstract: A detailed study of guided modes in a nanoscale metallic rectangular waveguide is presented by using the effective dielectric constant approach. The guided modes, including both traditional waveguide mode and surface plasmon mode, are investigated for the silver rectangular waveguide. The mode evolution in narrow waveguide is also discussed with the emphasis on the dependence of mode dispersion with waveguide height. Finally, the red-shift of the cutoff wavelength of the fundamental mode is observed when the waveguide height decreases, contrary to the behavior of regular metallic waveguide with PEC boundary. The comprehensive analysis can provide some guideline in the design of subwavelength optical devices based on the dispersion characteristics of metallic rectangular bore.

Efficient Mode Converter for Coupling between Fiber and Micrometer Size Silicon Waveguides

Abstract: A low-loss polarization independent mode converter for coupling standard single mode fiber to a silicon chip is presented. For a micrometer size silicon waveguide, we demonstrate a coupling loss of 1-1.5 dB/facet.

Electro-optic waveguide polarisation modulator

Abstract: An electro-optic waveguide polarisation modulator (20) comprising a waveguide core (4) having first and second faces defining a waveguide core plane, a plurality of primary electrodes (22, 24) arranged at a first side of the waveguide core plane and out of said plane, and at least one secondary electrode (26) arranged at a second side of the waveguide core plane and out of said plane, wherein the electrodes (22, 24, 26) are adapted in use to provide an electric field having field components (13, 15) in two substantially perpendicular directions within the waveguide core (4) so as modulate the refractive index thereof such that electromagnetic radiation propagating through the core (4) is converted from a first polarisation state to a second polarisation state.

Mode Coupling in Plastic Optical Fiber Enables 40-Gb/s Performance

Abstract: We report 40-Gb/s capability of 50-mum core plastic optical fiber using differential modal delay measurements and power penalty due to intersymbol interference computations. The results are explained via a comprehensive multimode fiber model that includes mode coupling (MC) and differential modal attenuation (DMA). We show that strong MC can enable 40-Gb/s transmission for reach in excess of 100 m even in the presence of irregularities in the refractive index profile that prevent 10-Gb/s performance without MC. Furthermore, we show that DMA effects are negligible and that the mode power distributions are not a good indicator of bandwidth.

Transmission loss of phase-shifted fiber Bragg gratings in lossy materials: a theoretical and experimental investigation.

Abstract: Narrow linewidth transmission filters in lossy materials based phase-shifted fiber Bragg gratings have been investigated experimentally and analytically. A novel matrix technique has been developed in calculation of the transmission loss and linewidth. The elements of the matrix simply consist of the coefficients of the coupled mode equations. Simulation shows a small fiber loss could result in a significant transmission loss, which has not been explained properly yet to our knowledge. For phase-shifted gratings in erbium-doped fibers, the absorption could result in over 20 dB loss at transmission wavelengths. Such an approach can also be used to analyze cladding modes, radiation mode, and complex structure gratings.