Showing papers on "Radiation mode published in 1993"

Radiation modes and the active control of sound power

Abstract: Two formulations for calculating the total acoustic power radiated by a structure are compared; in terms of the amplitudes of the structural modes and in terms of the velocities of an array of elemental radiators on the surface of the structure. In both cases, the sound radiation due to the vibration of one structural mode or element is dependent on the vibration of other structural modes or elements. Either of these formulations can be used to describe the sound power radiation in terms of a set of velocity distributions on the structure whose sound power radiation is independent of the amplitudes of the other velocity distributions. These velocity distributions are termed ‘‘radiation modes.’’ Examples of the shapes and radiation efficiencies of these radiation modes are discussed in the cases of a baffled beam and a baffled panel. The implications of this formulation for the active control of sound radiation from structures are discussed. In particular, the radiation mode formulation can be used to provide an estimate of the number of independent parameters of the structural response which need to be measured and controlled to give a required attenuation of the radiated sound power.

Optical properties of photosensitive fiber phase gratings

Abstract: The authors measure and calculate the optical properties of strong ( delta n/n approximately 10/sup -3/) in-core optical fiber phase gratings written by the UV laser sidewriting technique. A pronounced fine structure on the main reflection peak is observed and explained, along with a short wavelength loss associated with radiation mode coupling, modulated by cladding effects. >

High-gain, waveguide-fed antenna having controllable higher order mode phasing

Abstract: A diverging shell antenna fed by waveguide supplying TE₁₁ mode is described. A dielectric rod (46) partially contained within the waveguide (36) converts the TE₁₁ mode to a dominant or HE₁₁ mode. The HE₁₁ mode is controllably converted to second and third order modes in the diverging shell (30) by discontinuities (54) placed in predetermined locations in the diverging shell. The discontinuities (50,52) generating the second mode are incorporated into the dielectric rod structure (46). Turning of the relative amplitude and phase of the second and third order modes relative to the HE₁₁ mode is achieved by slideably positioning the dielectric rod (46). An alternative embodiment of the inventive device includes a reactive surface of the diverging shell.

Optical Waveguide Theory by the Finite Element Method

Abstract: Fiber optics, nanophotonics, Full Text: FreePDF18. 6MB.Abstract-A vector H-field finite-element method has been used for the solution of. Modulators in integrated optics has prompted the theoretical investigation of.finite element method is widely recognized as a. optical waveguides, particularly structures with arbitrary. 1 Koshiba, M, Optical Waveguide Theory by the.This paper reviews the application of the finite element method to analysis of. Therefore, there is a great interest in theoretical methods of waveguide analysis.Finite Element Methods for Nonlinear Optical Waveguides. This book addresses the problem of analysing non-linear optical waveguide structures. And uses supermodcs and coupled-mode theory to study optical switches, spatial solitons.This method is computationally more efficient than finite elements FE, thus allowing the use of finer meshes. Waveguide: the continuous line corresponds to the exact theoretical solution for the H. see 25, for.interest in theoretical methods of waveguide analysis. Finite Element Method FEM gives the elaborate and in depth analysis of the waveguide problems in.reflection in the finite element method to biaxial media and derivation of closed form expressions for the numerical reflection. 2 Verification of the theoretical reflection error. 4 Bending loss in an integrated optic rib waveguide. Finite Element Method constitutes one of the most powerful numerical methods when. Optical Waveguides have been used for decades giving the ability to transfer the information. Followed as the theoretical basis for the application. In this.quasi-TEM finite element method with numerical conformal mapping, and provides the. Matching with the optical signal, low microwave attenuation, and good. Koshiba, Optical Waveguide Theory by the Finite Elements Method, KTK.programs, and even improve the conventional optical waveguide theories.

Single longitudinal mode pumped optical waveguide laser arrangement

Abstract: An optical waveguide laser arrangement includes a solid optical waveguide having a waveguiding portion that extends along an axis between two spaced regions of the optical waveguide and is of a material capable of emitting stimulated light upon excitation by pumping light that is launched into the optical waveguide for axial propagation through the axially spaced regions of the optical waveguide Two reflectors are provided, each being disposed at one of the axially spaced regions of the optical waveguide to delimit a laser resonator At least one of the reflectors is constituted by a Bragg grating consisting of a multitude of axially consecutive periodic perturbations in the refractive index of the respective one of the axially spaced regions that cumulatively reflect the stimulated light at a reflectivity that decreases for adjacent longitudinal modes of the stimulated light with increasing deviation from a central wavelength The axial length of the laser resonator, the reflectivity of the Bragg grating and the gain of the excitable material are so coordinated with one another as to sustain lasing in only a single longitudinal mode

Integrated optics chips and laser ablation methods for attachment of optical fibers thereto for linbo3 substrates

Abstract: An integrated optics device has a substrate of lithium niobate (LiNbO3) with at least one optical waveguide. A slot formed in the edge of the substrate has end wall that exposes an end surface of the optical waveguide formed at an end surface angle with the optical axis of propagation to reduce reflected light in the optical waveguide. A length of optical fiber. The optical fiber has an end face formed at an end face angle with the direction of the propagation of light in the optical fiber. The slot is formed to receive the optical fiber. The optical fiber is positioned in the slot with the end face butt-coupled to the end surface of the optical waveguide to form an interface such that light may propagate between the optical waveguide and the optical fiber. A means for mounting the substrate. The optical waveguide is extended to an input junction with a center wave guide and with an sense waveguide. A first and second barrier trench or channel is formed adjacent to and substantially parallel with the center waveguide and offset from the waveguide by a predetermined distance. A portion of optical waveguide extending from the slot to the input junction is doped with a rare earth ion suitable for use as a light source when end pumped by light from the end face. The length of sense waveguides is selected to be greater than the coherence interval of the light source.

Mode evolution type polarization splitter on InGaAsP/InP

Abstract: A new type of mode-evolution polarization-splitter based on InGaAsP/lnP has been designed and realized. The component uses the large waveguide birefringence of the first-order TE and TM modes in a ridge waveguide made in a heterostructure, In the input section an asymmetric Y-junction acts as a mode converter in order to inject first-order TE- and TM-modes in a polarization-splitting section, which consists of a Y-junction formed by a bimodal and a monomodal waveguide. In the output section a third Y-junction is connected to the bimodal waveguide to couple the first-order mode to a monomodal output waveguide. Components that are 6-mm long and show polarization splitting at a wavelength of 1.55 mu m have been realized. The best splitting ratios are close to -20 dB, which is in agreement with BPM simulations. Excess losses are below 1 dB. >

New formula for semiconductor laser facet reflectivity

Abstract: An analytic expression for the main mode reflectivity of a multicoated laser facet at normal incidence is derived using the free space radiation mode technique. This uses exact guided modes, and accurately models the radiation modes near the facet. The results compare favorably with exact TE and TM benchmarks while retaining the simplicity and speed of the Fresnel approximations. >

Low bend loss singlemode optical waveguide fiber

Abstract: An optical waveguide fiber with improved bend loss performance while maintaining cutoff wavelength, λc, and zero dispersion wavelength, λ0, in practical operating ranges. The fiber includes an inner core region with a refractive index delta higher than the rest of the core and a reduced diffusion tail at the core/cladding interface. Optionally, a ring at the outer portion of the core is provided to compensate for increased λ0 which results from the higher inner core refractive index delta. This ring also contributes to the reduced diffusion tail at the core/cladding interface.

Beam quality factor of the LP01 mode of the step-index fiber

Abstract: The beam quality factor M2Q of the LP01 mode of the step-index fiber is calculated in a closed form. Propagation of the mode through an optical system can thereafter be described using the ABCD ray's matrix.

Optical sensor having a floatation means for detecting fluids through refractive index measurement

Abstract: The present invention provides methods and systems for sensing the presence of fluids, such as hydrocarbon-based liquids and/or water, in an ambient environment based upon their light refractive properties. An optical waveguide is deployed in the environment (or a sample chamber disposed within the environment), such that the transmittance of light through the waveguide is attenuated in the presence of the fluid analyte. In one preferred embodiment, the light source is aligned with the waveguide, such that the light entering the waveguide enters one end at an angle relative to the central axis of the waveguide and propagates by internal reflection within the waveguide. Optimal propagation occurs in the absence of the fluid while the presence to the fluid in contact with the waveguide walls causes detectable losses in light propagation due to degradation of the internal reflectance.

Optical fiber characterization by simultaneous measurement of the transmitted and refracted near field

Abstract: An experimental setup is presented which permits, in a routine way for R&D purposes, simultaneous measurement of the transmitted near field at 1300 nm and 1550 nm, and the refracted near field at 820 nm. A new method for the calibration of the refractive index is proposed. The obtained accuracy for the refractive index is dn+or-0.0002. The reproducibility of measurements of geometrical parameters like the mode field diameter, the core and cladding diameters, and concentricity error, is +or-0.1 mu m. Measurements of the mode field as a function of polarization state for four different hi-bi fiber are presented. >

Detailed comparison of two approximate methods for the solution of the scalar wave equation for a rectangular optical waveguide

Abstract: Two approximate methods for the determination of the fundamental mode of an optical waveguide with rectangular core cross section and step refractive-index profiles are presented and analyzed thoroughly. Both methods are based on Galerkin's method. The first method uses Hermite-Gauss basis functions and the second uses the guided and nonguided slab waveguide solutions as basis functions. The results are compared with results from an accurate circular harmonic analysis. Both methods provide values of the normalized propagation constant with errors less than 0.1% for practical rectangular single-mode waveguides. The slab waveguide method is the fastest, and even when only one slab waveguide mode is used the propagation constant for the fundamental mode can be calculated with an error of less than 1%. The slab waveguide method also gives very accurate results for the propagation constant for higher order modes. >

'Free space radiation mode' method for the analysis of propagation in optical waveguide devices

Abstract: A radiation mode technique, first used in optical fibre theory, is used to study the propagation of waves in practical optoelectronic devices. The method is validated against other techniques for step discontinuities, tapers, air-gaps and Y junctions. The solution deals successfully with reflected waves and is found to be accurate enough to be used for design purposes.

Ion-beam deposited, gain enhanced ring resonators

Abstract: An optical waveguide is created using the process of ion beam deposition resulting in a waveguide with low propagation loss, mode discrimination, and gain characteristics. The waveguide is made up of a multilayer stack which is deposited upon a thermally stable substrate, wherein the multilayer stack comprises alternating layers of a first material and a second material. The layers of second material are doped with a rare earth material. By pumping the waveguide with a pump light source, interaction between the pump light and the rare earth material within the waveguide causes amplification or gain of a first optical signal. Ion beam deposition is used to fabricate the waveguide, therefore production of a high quality rare earth doped waveguide is possible. Furthermore, the waveguide is made using batch processing thus reducing costs.

Nonlinear optical coupler using a doped optical waveguide

Abstract: An optical mode coupling apparatus includes an Erbium-doped optical waveguide in which an optical signal at a signal wavelength propagates in a first spatial propagation mode and a second spatial propagation mode of the waveguide. The optical signal propagating in the waveguide has a beat length. The coupling apparatus includes a pump source of perturbational light signal at a perturbational wavelength that propagates in the waveguide in the first spatial propagation mode. The perturbational signal has a sufficient intensity distribution in the waveguide that it causes a perturbation of the effective refractive index of the first spatial propagation mode of the waveguide in accordance with the optical Kerr effect. The perturbation of the effective refractive index of the first spatial propagation mode of the optical waveguide causes a change in the differential phase delay in the optical signal propagating in the first and second spatial propagation modes. The change in the differential phase delay is detected as a change in the intensity distribution between two lobes of the optical intensity distribution pattern of an output signal. The perturbational light signal can be selectively enabled and disabled to selectively change the intensity distribution in the two lobes of the optical intensity distribution pattern.

Bend-induced loss for the higher-order spatial mode in a dual-mode fiber.

Abstract: Measured loss for the LP11 mode in a dual-mode fiber subjected to a uniform bend shows a strong dependence on the orientation of the mode-field pattern relative to the plane of the fiber bend. Wavelength and bend-radius dependence of the loss indicates that operation within ~40 nm of cutoff is feasible in dispersion compensators based on dual-mode fibers operated in the LP11 spatial mode near cutoff.

Long-range optical modes supported by a strongly absorbing thin organic film

Abstract: We report the observation of the optical excitation of a long-range mode supported by coupling to Frenkel-type excitons in a highly absorbing organic thin film of metal-free phthalocyanine. The long-range mode is examined over a wavelength range from 400 to 740 nm, and the results are compared both with Fresnel’s theory for planar systems and with analytic expressions that describe the mode in the thin-film limit. Numerical analysis shows that this long-range mode, which like the long-range coupled surface mode has a quadratic dependence of wave vector on film thickness, actually evolves from a TM0 bulk polariton mode. We call the mode that we have observed a long-range excitonic guided mode.

Optical fiber type diffraction grating

Abstract: PURPOSE:To increase the reflectivity and to make it possible to change a selection wavelength by applying periodic refractive index changes to a specific core by irradiation with light to form diffraction gratings. CONSTITUTION:An optical fiber structure having the core consisting of a polymer or polysilane dispersed with a low molecular compd. is constituted by imparting the periodic refractive index changes to the core by irradiation with light, thereby forming diffraction gratings. The optical fiber structure in such a case means a structure obtd. by covering the core having a high refractive index with a clad having a low refractive index and includes not only such a three-dimensional optical waveguide as represented by an optical fiber in a narrow sense but a two-dimensional optical waveguide as well. As the low molecular compd., a compound which generates, for example, charges and a charge transfer with the polymer to change the refractive index when the compd. is irradiated with the light of the prescribed wavelength, is used. The polymer is not particularly limited and various kinds of the polymers are usable.

Enhanced dominant mode operation of a shielded multilayer coplanar waveguide via substrate compensation

Abstract: The cutoff frequency of the first higher-order even mode in a shielded multilayer coplanar waveguide (CPW) is studied using the spectral domain approach (SDA). The effective dielectric constant for the dominant odd and first higher-order even mode in a shielded multilayer CPW is computed and compared to other published numerical results. Dielectric constant and substrate height are varied with respect to even mode cutoff frequency and plotted for several CPW structures. Different combinations of internal substrates are shown to produce even mode cutoff frequency maximization for increased odd mode operation bandwidth. >

Spatial soliton switching modes of nonlinear optical slab waveguides

Abstract: A planar nonlinear waveguide, consisting of a linear substrate, a linear film, and a Kerr-type cladding and end-fire excited by the TE0 mode of a linear planar waveguide, is studied both numerically and analytically (by means of the equivalent-particle model). It is shown that a switching device whose output is controlled by the input optical power can operate not only in the well-known soliton-breakup mode but also in a low-power mode. Furthermore, the device is shown to be highly sensitive to ak0, the product of the guide half-width times the wave number of the incoming beam.

Optical wavelength converter

Abstract: An optical wavelength converter comprises a substrate, a first waveguide formed in the substrate and allowing a fundamental wave to enter therein, and a second waveguide extending parallel to the first waveguide and disposed on the substrate at a predetermined distance spaced from the first waveguide, wherein the second waveguide has refractive index gratings formed and arranged periodically in the extending direction thereof, each refractive index grating having an equivalent refractive index different from that of the second waveguide. The optical wavelength converter is of high conversion efficiency.

Wideband TM01 -to-TE11 circular waveguide mode convertor

Abstract: The mode convertor employs two intermediate modes, a coaxial TEM and a rectangular waveguide TE 10 mode, in the transition between the TM 01 and TE 11 circular waveguide modes. The coaxial line provides isolation while acting as a mode filter between the device input and output ports. The rectangular waveguide provides a wide mode separation ratio between the TE 10 and TM 11 modes. The TE 10 mode then transitions into the TE 11 in the circular output waveguide. The coaxial section keeps the output TE 11 mode from scattering back to the input, and the rectangular section keeps the TM 01 from being excited in the output.

Confocal laser scanning microscope with dual mode waveguide

Abstract: A confocal laser scanning differential interference microscope includes an illumination optical system for radiating a laser light spot onto an object, a focusing optical system for focusing light reflected by the object onto a detection surface, a detection optical system for detecting the reflected light focused on the detection surface, a scanning device for scanning the laser light spot relative to the object, and an optical element arranged between the focusing optical system and the detection optical system, and having a waveguide device for propagating the reflected light focused by the focusing optical system. The waveguide device has waveguides in at least two directions perpendicular to the optical axis of incident light. The waveguides constitute a double-mode transmission waveguide, which selects either of a combination of a 0th-order mode and a 1st-order mode and the 0th-order mode alone in each of the two directions of the reflected light from the object according to amplitude distributions of electric fields in the two directions of the incident light as waveguide modes in the two directions upon propagation of the incident light, and propagates light in the selected modes. The detection optical system receives light emerging from the waveguide, and detects whether the waveguide in each of the two directions is the combination of the 0th-order mode and the 1st-order mode, or the 0th-order mode alone, thereby detecting amplitude distributions of the electric fields, in the two directions, of the reflected light from the object.

Semiempirical relation for curved optical waveguide design in the edge-guided mode regime

Abstract: A semiempirical relation has been developed for determining the minimum allowable radius of curvature of a circular waveguide with an edge-guided fundamental mode. The specified parameters are the wavelength, the effective refractive index of the waveguide, the lateral index step, and the allowable radiation loss coefficient. This relation was fitted and verified against numerically evaluated solutions of Maxwell's equations in two dimensions for lateral index steps 0.01 >

Mode evolution in optical resonators with a radial gain profile.

Abstract: A Fox and Li analysis [Bell Syst. Tech J. 40, 453 (1961); Proc. IEEE 51, 80 (1963); IEEE J. Quantum Electron QE-4, 460 (1968)] for a laser resonator with a radially varying gain yields a picture of the mode evolution dynamics and a steady-state mode distribution which are different from the constant-gain case. When an axially maximal gain is sharply peaked, the mode-settling time is markedly reduced and the final mode distribution is more tightly focused. When the gain distribution is sharply annular, an annular or ``doughnut''-shaped mode develops. In some intermediate cases, which may be relevant to some gas lasers, a stable transverse mode never definitively evolves. Misalignments of the gain with the cavity yield distortions to the mode shape and these are also explored.

Silicon-on-insulator optical rib waveguide circuits for fiber optic sensors

Abstract: Optical rib waveguides have been formed in silicon-on-insulator structures. The effects of rib waveguide dimensions on mode and loss characteristics have been studied. Waveguides with dimensions compatible with single mode optical fibers have exhibited single mode behavior with low loss. The compatibility of these silicon-on-insulator waveguide structures with optical fibers, combined with the ability to form active optical modulators in silicon based on free carrier injection/depletion is encouraging for the future use of silicon guided optics in fiber optical and integrated optical sensors. The use of SOI active waveguide circuits for closed loop AC dither fringe detection in interferometric sensors is a possible application area.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical waveguide and optical waveguide device

Abstract: Optical device including an optical waveguide composed of a LiTaO3 monocrystalline substrate and a LiNbO3 monocrystalline thin film waveguide formed on the surface of the substrate, with the lattice length of the LiNbO3 monocrystalline thin film waveguide and the LiTaO3 monocrystalline substrate being matched with each other, and an electrode provided on at least one of the branched sections of the waveguide extending along the optical axis thereof for changing a refractive index of the waveguide. The optical device having the optical waveguide has excellent electro-optic effects and a resistance to optical damage as well as an advanced modulation efficiency and a stable amplitude modulation.

Methods and apparatus for generating plasma, and semiconductor processing methods using mode restricted microwaves

Abstract: A plasma processing apparatus has a waveguide along which microwaves are propagated from a microwave generator to a plasma-forming region in a low-pressure processing chamber. The waveguide has a large cross-sectional area, to enable a large region of plasma to be achieved. Uniformity and stability of the plasma are improved by a mode restrictor which inhibits mixing of propagation modes which is otherwise liable to occur in a wide waveguide. The mode restrictor consists of electrically-conductive dividers which divide the waveguide cross-section into an array of sub-guides before the plasma-forming region.

Influence of mode competition on the fast wavelength switching of three-section DBR lasers

Abstract: For a three-section distributed Bragg reflector (DBR) laser, the dependence of the intermodal wavelength-switching time on the precise wavelengths within two longitudinal modes is examined experimentally and theoretically. When switching from a fixed wavelength in the central region of the tuning curve for one mode to a second wavelength on the tuning curve for another mode, a significant variation of the switching delay occurs as the second wavelength spans the mode tuning curve. Mode competition is identified as being responsible for this variation. >