Showing papers on "Radiation mode published in 1992"

Dual mode coupling by square corner cut in resonators and filters

Abstract: A method for realization of dual-mode coupling in rectangular waveguide cavities is described and analyzed. The method completely replaces the coupling screw, and therefore can be used to eliminate the need for tuning in dual-mode waveguide cavity filters. It also offers a wide range of coupling values and can achieve higher power-handling capability than coupling screws. Mode matching is used to calculate the mode chart of the infinitely long square corner cut rectangular waveguide (SCCRW), the field distributions of each mode, and the resonant frequencies of the cavity. An evanescent mode rectangular waveguide is used to provide dual-mode couplings between adjacent cavities. The junction discontinuity between the SCCRW and the rectangular waveguide is modeled by a double mode-matching method, yielding modal scattering parameters of the junction. A four-pole dual-mode elliptic-function rectangular waveguide cavity filter using the coupling method was constructed. The experimental filter results showed excellent agreement with theory. >

Broadband dispersion compensation by using the higher-order spatial mode in a two-mode fiber

Abstract: A fiber-optic technique for compensating both first- and second-order group-velocity dispersion in single-mode fiber spans is demonstrated by using the large waveguide dispersion that occurs for the higher-order (LP11) spatial mode in a two-mode fiber near cutoff. Complete restoration of 7-ps pulses that had been dispersed by a factor of 10 in 5 km of single-mode fiber is demonstrated over a 20-nm-wavelength window. First-order dispersion as large as −228 ps/(nm km) is observed for the LP11 mode at 1560 nm in the two-mode fiber.

Index-and-dimensional taper and its application to photonic devices

Abstract: A mode-field-converting optical channel waveguide with tapered refractive index and cross-sectional dimensions is proposed. In this waveguide, both the refractive index and cross-sectional dimensions of a core are adiabatically varied along a propagation direction in such a way that the normalized frequency V of the waveguide may be kept constant. Since radiation loss caused by waveguide imperfections is strongly dependent on the V value, the waveguide has good mode-field-converting capability without causing high radiation loss. Layer thickness and index of a core of a silica waveguide were tapered by modulating a raw material gas flow in a flame hydrolysis deposition method, and a channel width taper was formed by a photolithographical technique. In order to confirm the usefulness, taper waveguides have been used (1) to achieve good field matching between a fiber and a guided-wave optical switch, and (2) to fabricate a fiber-compatible monolithic 32*32 star coupler in a small chip. >

Erbium-doped ion-exchanged waveguide lasers in BK-7 glass

Abstract: Ion-exchange in glass is a simple, flexible technique to realize optical fiber-compatible planar waveguide devices. Recently, neodymium-doped waveguide lasers operating at 1060 and 1300 nm have been demonstrated in this technology. Lasers operating at 1540 nm are desirable for telecommunication applications and the authors report for the first time ion-exchanged waveguide lasers in erbium-doped glass emitting at this wavelength. Lasers in BK-7 glass doped with 0.5 wt.% Er/sub 2/O/sub 3/ and pumped at 980 nm exhibited launched pump power thresholds of 150 mW and slope efficiencies of 0.55%. The waveguides operated in a single transverse mode at the lasing wavelength. >

Single-mode selection using coherent imaging within a slab waveguide CO2 laser

Abstract: A technique for selecting a single high‐order lateral mode of a rf excited slab waveguide laser is described. An in‐cavity grid which matches the periodicity of the desired mode, together with slab waveguide dimensions which create coherent imaging by the Talbot effect, have produced a stable output power of 155 W in a high spectral purity, single‐resonator mode.

Mode competition using TE03 gyrotron cavities

Abstract: The gyrotron is a powerful source of millimetre wave radiation. Fusion applications require more power per tube than is currently available This in turn means that the resonator must be highly overmoded, with a dense mode spectrum, which leads to mode competition. The influence of external parameters, such as the applied magnetic field, electron beam, and resonator geometry, on mode competition in tubes designed to operate at 150 and 140 GHz in the TE03 mode is investigated theoretically and experimentally. It can be shown that even when the mode spectrum is fairly dense, single mode operation of a gyrotron is possible. The influence of startup conditions on output power is investigated in the 150 GHz experiment. In some cases, modes with an axial index of 2 were excited.

Widened output mode semiconductor optical component and method of fabricating it

Abstract: A widened output mode semiconductor optical component such as a laser includes superposed active and passive waveguides. The width of the active waveguide decreases in a rear part of a mode transition section to couple a "narrow" optical mode which is amplified and guided by the active waveguide to a "wide" mode which is guided by the passive waveguide and which has a mode size greater than that of the narrow mode. The width of the passive waveguide then decreases in a front part of this section to couple the wide mode to an even wider circular mode. The invention finds applications in the fabrication of optical heads for optical fiber telecommunication networks.

Mode coupling and phase modulation in vibrating waveguides

Abstract: When coherent light is coupled into a multimode waveguide (such as a fiber), a speckle pattern is formed at the fiber output. When the fiber is vibrated, the speckle pattern is modulated due to mode coupling and phase modulation of the waveguide modes. It is shown that when a highly coherent light source is used, the speckle pattern modulation is due primarily to phase modulation of the modes. When less coherent sources are used (such as low-cost laser diodes), mode coupling is the dominant effect. >

Waveguide type optical device and method for manufacturing the same

Abstract: A method for fabricating a waveguide type optical device is disclosed, through which a core and a reference plane are obtained at the same time by etching a core layer using a thin layer of a predetermined shape formed on the core layer as a mask. In this waveguide type optical device, the core is easily coupled with an optical element such as an optical fiber by means of the reference plane.

Optical system having a ring-shaped waveguide

Abstract: An optical connector comprises a ring-shaped waveguide and a straight waveguide for introducing a light beam into the waveguide. These waveguides are arranged on a substrate in a manner such that the gap between their nearest positions is not longer than the wavelength of the light beam. The radius, width, thickness, and refractive index distribution of the ring-shaped waveguide are set so that a light beam with a wavelength λ=2πr/n (r and n are the radius of the ring-shaped waveguide and a certain natural number, respectively) continues to circulate therein. A grating having a cycle of 2πrλ/(2πr+λ) or 2πrλ/(2πr-λ] is formed on the surface of the ring-shaped waveguide.

Semiconductor optical waveguide type switch including light control means

Abstract: A semiconductor waveguide type all-optical switch of a simple structure which can switch at high speed with low switching energy. A waveguide is formed within a core layer made of a semiconductor for absorbing controlling light when an electric field is applied, and a pair of electrodes are formed for applying a voltage to a waveguide part where a refractive index change is to be caused. The controlling light together with controlled light is entered in the waveguide. When a voltage is applied, Franz-Keldysh effect causes the wavelength at the optical absorption spectrum edge in the refractive index change part to shift to the long wavelength side. If light of a wavelength satisfying a predetermined condition is used as the controlling light, the controlling light is absorbed only in the refractive index change part for changing the refractive index in the part, thus the controlled light is switched. Preferably, a p-i-n structure is adopted.

Dual waveguide probes extending through back wall

Abstract: Waveguide OMT, which can be utilized as an antenna feed, has two orthogonally polarized coaxial ports extending through the back wall of the waveguide. Cross coupling between the probes is minimized by locating the point of entry through the back wall and orienting each probe such that it couples to a primary waveguide mode, but does not couple to the first higher waveguide mode, or, for coaxial waveguide, does not couple to the TEM mode.

Magneto-Optic Devices using Interaction between Magnetostatic Surface Wave and Optical Guided Wave

Abstract: An analysis of the optical TE-TM mode conversion by magnetooptic effect induced by magnetostatic surface wave (MSSW) is discussed. A typical MSSW waveguide has a thick layer for the convenient excitation of MSSW. However, the waveguide is not a single mode waveguide but multi-mode for the optical wavelength of 1.3 [µm]. We propose here the multi-layer waveguide consisting of the thin and thick magnetic layers that improves the characteristics of optical mode conversion. The efficiency of 100% is achieved over the interaction length of about 1.0 [cm] for the applied microwave power density of a few [mW/mm].

Optical waveguide (te,tm) mode converter

Abstract: Mode converter for converting a fraction of one guided mode of an optical signal in an incoming optical waveguide section (A) into another guided mode in an outgoing wave-guiding section (C) by means of a periodic coupling between both guided modes in an intermediate optical waveguide section (B). The intermediate section (B) has a periodic geometrical structure as a result of an N-fold periodic sequence of two light-guiding subsections (P, Q) within a period length (LP +LQ). The sequence can be obtained by arranging for the waveguide profiles of the subsections to differ from one another, preferably as a result of differences in width. The sequence can also be obtained by offset joining of the two subsections with the same waveguide profiles. Advantages are: the high degree of integrability, the ability to co-integrate a laser light source in an optical section of a coherent optical receiver and the achievement of a new integrated design of such an optical section, which design is free of metallized elements.

Tunable optical waveguide coupler

Abstract: Various optical functions are generated in accordance with the present invention of a novel broadly tunable monolithic wavelength selective coupler which can be integrated with a gain medium to form a broadly tunable laser. The tunable wavelength selective coupler supports a pair of asynchronous waveguides, an upper waveguide and a lower waveguide, in combination with a phase match course grating for coupling optical energy between said waveguides. One end of the lower waveguide terminates at an output facet. The corresponding end of the upper waveguide terminates in an optical signal absorbing medium. The other end of the lower waveguide is terminated to prevent optical energy from entering the waveguide; and, the corresponding end of the upper waveguide terminates at an input facet. The combination of a gain section and the monolithically tunable wavelength selective coupler forms a broadly tunable laser which is an important source of optical energy for a number of applications such as wavelength division multiplexed networks and switching systems. The laser frequency is determined by that wavelength λo which satisifies the forward coupling phase match condition, λg=Λ|N2 -N1 | of the coupler where Λ is the coarse grating period and N1, N2 are the effective indices of the two waveguides. Wavelengths which are not coupled from the upper waveguide to the lower waveguide are attenuated in the optical signal absorbing means. Tuning of the laser wavelength is achieved by either injecting current into or applying a reverse bias voltage to the upper waveguide to decrease or increase its index respectively and change the coupled wavelength.

Mode field conversion fiber component

Abstract: The present invention provides a mode field conversion fiber component formed by fusion-connecting connection end surfaces of two optical components having different mode fields. The mode fields of the two optical components are conformed to each other at the connection end surfaces, and are continuously varied near the connection end surfaces. The present invention also provides a method for manufacturing a mode field conversion fiber component, having the steps of butting connection end surfaces of two optical fibers having different mode fields, fusion-connecting the connection end surfaces of the two optical fibers, and heating a fusion-connecting portion of the connection end surfaces, diffusing core dopant, and conforming the mode fields of the two optical fibers.

Generalized Jaynes-Cummings model with atomic motion

Abstract: Following the recent experiments in the elementary Bose-Fermi interaction, we extend the Jaynes-Cummings model, to include the atomic motion and the mode structure. Using the above extended model, we study the quantum noise distribution in the two quadrature components of the radiation mode.

Second Harmonic Generation in Nb2O5 Thin-Film Optical Waveguide Deposited on LiTaO3 Substrate by RF Magnetron Sputtering

Abstract: The first experimental observation of Cerenkov-type second harmonic generation (SHG) in an amorphous Nb2O5 thin-film optical waveguide on (0001) LiTaO3 substrate is reported. The Nb2O5 thin films were deposited by rf magnetron sputtering on LiTaO3 substrate. A Nd:YAG laser at 1064 nm wavelength was used as the pumping source for the SHG experiments. The conversions occurred between the fundamental (1064 nm) TE0 guided mode and the harmonic (532 nm) TM radiation mode, and between the TM0 guided mode and the TM radiation mode. The efficiency of both conversions was about 10-8 for a sample with a film thickness of 788 nm. These SHG results were in good agreement with the coupled-mode theory, and the theoretical calculation revealed that the low conversion efficiencies were due to the unsuitable film thickness. It was predicted that the efficiencies could be raised to a much higher level.

Optical waveguide device and method for connecting optical waveguide and optical fiber using the optical waveguide device

Abstract: An optical waveguide device which can be connected with an optical fiber through a simple positioning adjustment. The optical waveguide device comprises a substrate, a first cladding with a uniform thickness formed on the substrate, a core formed on the first cladding, a recognizable thin layer formed on the first cladding on both sides of the core, and a second cladding formed on the first cladding so as to cover the core. The thin layer is parallel to the top surface of the substrate and defines a reference plane which is substantially in the same plane as the bottom surface of the core. Connection of the optical waveguide device with the optical fiber is achieved by bringing the reference plane into contact with a plane which is in a predetermined relative position to the optical fiber and only making a planar positioning adjustment with the planes held in contact.

Optical polarization-state converting apparatus for use as isolator, modulator and the like

Abstract: In a polarization-state converting apparatus for use as an optical isolator, an optical modulator and the like, there are provided a waveguide including a magnetic semiconductor, a device for applying a magnetic field to the waveguide in a first predetermined direction, a device for applying an electric field to the waveguide in a second predetermined direction, and a mode conversion is caused via electrooptic and magnetooptic effects due to the electric and magnetic fields to change the polarization state of light propagating through the waveguide. When used as an optical isolator, the optical isolation is performed to compensate for degradation of the mode conversion rate due to a phase mismatch between light incident upon the waveguide and light emerging from the waveguide. When used as an optical modulator, the optical modulation of light emerging from the waveguide is performed by varying the electric field and an optical isolation function is effected while compensating for degradation of the mode conversion rate due to a phase mismatch between light incident upon the waveguide and light emerging from the waveguide.

Asymmetric, periodically loaded waveguide for polarization rotation

Abstract: Polarization rotation is achieved in an exemplary embodiment in an optical waveguide by augmenting the waveguide structure with a plurality of spaced-apart sections for loading the refractive index of the waveguide to cause a lateral asymmetry in the refractive index profile of the waveguide viewed in the plane transverse to the waveguide longitudinal axis. Each spaced-apart section induces non-zero coupling between the principal orthogonal polarization modes. Phase matched coupling between the principal orthogonal polarization modes is achieved by spacing the sections periodically by a distance Λ equal to λ/ΔN where λ is the propagation wavelength in the waveguide and ΔN is the difference between the effective refractive indices for the principal orthogonal polarization modes. Realizations of the waveguide structure are shown using Group III-V semiconductor rib waveguide structures.

Fiber type wavelength conversion element

Abstract: In a fiber type wavelength conversion element, which has a fiber core made of non-linear optical crystal and in which a wavelength of incident ight is converted by non-linear optical effects of the second order on the core, a clad material is used, which has a refractive index to satisfy a condition of: 0.95

Reconfigurable optical interconnection network for multimode optical fiber sensor arrays

Abstract: A single-source, single-detector architecture has been developed to implement a reconfigurable optical interconnection network multimode optical fiber sensor arrays. The network was realized by integrating LiNbO3 electrooptic (EO) gratings working at the Raman Na regime and a massive fan-out waveguide hologram (WH) working at the Bragg regime onto a multimode glass waveguide. The glass waveguide utilized the whole substrate as a guiding medium. A 1-to-59 massive waveguide fan-out was demonstrated using a WH operating at 514 nm. Measured diffraction efficiency of 59 percent was experimentally confirmed. Reconfigurability of the interconnection was carried out by generating an EO grating through an externally applied electric field. Unlike conventional single-mode integrated optical devices, the guided mode demonstrated has an azimuthal symmetry in mode profile which is the same as that of a fiber mode.

Optical waveguide enhanced laser to fiber coupling

Abstract: Apparatus for improving the coupling efficiency of a laser to a single mode fiber by means of an intermediate waveguide is disclosed. For uniform waveguides maximum improvement results when waveguide's mode field radii MFR is designed as the geometrical mean of the MFR of the laser and the MFR of the fiber. The apparatus can be extended to multi-stage couplers. Each successive stage is designed to have a spot size which is the geometric mean of the section before and after. With only a small number of stages significant improvement in coupling efficiency can be realized.

Design of strip-loaded optical waveguides for low-loss coupling to optical fibers

Abstract: Mismatch between the fundamental mode of a waveguide and that of an attached optical fiber may cause a significant loss of power in a guided-wave structure. These losses can be minimized, however, by proper shaping of the waveguide mode through judicious choice of dimensions and refractive indexes. It is shown by computer modeling and qualitative arguments that coupling losses between standard optical fibers (5-10- mu m modal diameter) and strip-loaded waveguides constructed of GaAs/AlGaAs may be reduced to less than 10% at each facet. A wavelength of 0.85 mu m is used as a specific example, with modal shapes explored systematically for a series of different waveguide structures. >

Coherent coupling of radiation modes in Mach-Zehnder electrooptic modulators

Abstract: The effects of the radiation modes in Mach-Zehnder GaAs electrooptic modulators are studied using the standard beam propagation method (BPM). The radiation mode contribution to the energy transfer in the passive structure is studied as well as the performances of the active device under modulation. For compact weakly guiding structures, a good geometrical design that takes into account the propagation of the radiation modes is not only effective in loss reduction but also important for improving the design of the active structure. A 20% change of the modulator bias voltage is predicted with a shortening of the interaction length from 5 to 4.6 mm. This result is better understood when one considers the coherent coupling of the radiation modes in the structure. >

Optical modes in a partially waveguided cavity

Abstract: The behavior of the optical beam in an FEL cavity is well understood in both the long- and short-wavelength limits. At long wavelengths the optical mode interacts strongly with the walls, which act as a waveguide. At short wavelengths the optical beam in an FEL is undisturbed by the walls; it propagates as a simple Gaussian. We are interested in the intermediate regime, where, as the wavelength increases, the optical mode grows and begins to feel the influence of the walls, causing the mode shape to distort and losses to occur. Using a Fox-Li technique to propagate in free space and a decomposition of the Gaussian beam into waveguide modes inside the undulator, we calculate the changes in mode shape and cavity losses as the wavelength increases. The resulting theory and numerical calculations are an important consideration for the design of mid- to far-infrared FEL systems.