Showing papers on "Mode scrambler published in 2005"

SBS threshold for single mode and multimode GRIN fibers in an all fiber configuration

Abstract: We investigate stimulated Brillouin scattering (SBS) threshold in single mode and multimode fibers in an all fiber network. The pump is a single mode fiber pigtail attached to a diode. We find the theory and experiment agree for both single mode and multimode GRIN fibers. We modify the bulk SBS threshold equation for use with fibers by properly accounting for mode sizes and modal dispersion.

Mode transformer for miniaturized optical circuits

Abstract: A novel mode transformer was fabricated that transforms a modal area by a factor of 100. Using the mode transformer improves the efficiency of mode transformation by an order of magnitude compared with that when no mode transformer is used. With this mode transformer, input–output coupling of miniaturized, on-chip integrated optical circuits to external optical fibers is achieved with low loss. The mode transformer’s design, fabricated in silicon, is scalable to virtually any waveguide size, facilitating continuous miniaturization in silicon optoelectronics.

Microbend-induced mode coupling in a graded-index multimode fiber

Abstract: We present a theoretical analysis of the mode coupling effects at a microbend along a graded-index (GI) multimode fiber (MMF). By matching the incident and excited mode fields at the microbend, we obtain the coupling coefficients among the guided modes at different microbending conditions. The theoretical results compare well with the experimental results from near-field measurements on a GI MMF subject to microbending. The usefulness of our theory is demonstrated with two applications: (i) an explanation of the operation principle of a wavelength-switchable fiber laser that contains a fiber Bragg grating in a GI MMF and (ii) quantification of the function of a microbend-based mode scrambler.

Coherent light source and optical device

Abstract: High power output can be easily obtained from a wide stripe laser, however, since its transverse mode is a multimode and an efficiency of coupling with a single mode waveguide and a single mode fiber is low, there have been problems in application to high-coherence devices. An oscillation mode of a semiconductor laser can be fixed to a single mode by feeding back beams projected from the wide stripe semiconductor laser to an active layer of the semiconductor laser, after having the beams permeate a mode transducer and a wavelength selecting filter.

Optical fiber transmission system with increased effective modal bandwidth transmission

Abstract: A multi-mode optical fiber link is described. The multi-mode optical fiber link includes a first spatial mode converter that is coupled to a first single mode optical fiber. The first spatial mode converter conditions a modal profile of an optical signal propagating from the single mode optical fiber to the first spatial mode converter. A multi-mode optical fiber is coupled to the first spatial mode converter. A second spatial mode converter is coupled to an output of the multi-mode optical fiber and to a second single mode optical fiber. The second spatial mode converter reduces a number of optical modes in the optical signal. Both the first and the second spatial mode converters increase an effective modal bandwidth of the optical signal.

Design of mode scramblers for step-index and graded-index plastic optical fibers

Abstract: We analyze the internal evolution of light power angular distribution in typical mode scrambling configurations by comparing the resultant far fields, obtained either experimentally or computationally, with the experimental equilibrium mode distribution (EMD) far field for the plastic optical fibers (POF) considered, so as to provide an insight that helps to adapt existing scramblers to new types of POF that are coming onto the market.

Experimental and theoretical characterization of the mode profile of single-mode DFB fiber lasers

Abstract: The characterization of the spatial mode profile of distributed feedback fiber lasers (DFB-FLs) is discussed. A new approximate solution for the mode profile of single longitudinal mode DFB-FLs with nonuniform phase and grating profiles is derived. An enhanced high resolution heat perturbation method for mode shape characterization is described. Experimental mode shape profiles are compared with theoretical predictions with good agreement.

New optical frequency domain differential mode delay measurement method for a multimode optical fiber.

Abstract: A novel mode analysis method and differential mode delay (DMD) measurement technique for a multimode optical fiber based on optical frequency domain reflectometry has been proposed for the first time. We have used a conventional OFDR with a tunable external cavity laser and a Michelson interferometer. A few-mode optical multimode fiber was prepared to test our proposed measurement technique. We have also compared the OFDR measurement results with those obtained using a traditional time-domain measurement method.

Adiabatic mode multiplexer for evanescent- coupling-insensitive optical switching

Abstract: A novel adiabatic mode multiplexer enables a 2 x 2 optical switch whose operation does not depend on accumulated phase due to evanescent coupling between waveguides. The adiabatic mode multiplexer has a negligible insertion loss over C+L bands and modal cross talk better than -40 dB for any polarization state. Mode multiplexing is achieved by adiabatic transition from the fundamental mode of the single-mode waveguide to the higher mode of the multimode waveguide. Experimental measurement results for a device realized in silica-on-silicon technology are presented. By directly measuring the nonadiabatic transition probability, we show that the adiabatic mode multiplexer operates in the Landau-Zener regime.

Planar Lightwave Circuit, Design Method for Wave Propagation Circuit, and Computer Program

Abstract: A planar lightwave circuit is provided which can be easily fabricated by an existing planar-lightwave-circuit fabrication process, which can lower the propagation loss of signal light and which can convert inputted signal light so as to derive desired signal light. A planar lightwave circuit having a core and a clad which are formed on a substrate, has input optical waveguide(s) (111) which inputs signal light, mode coupling part (112) for coupling a fundamental mode of the inputted signal light to a higher-order mode and/or a radiation mode, or mode re-coupling part (113) for re-coupling the higher-order mode and/or the radiation mode to the fundamental mode, and output optical waveguide(s) (114) which outputs signal light. The mode coupling part or the mode re-coupling part is an optical waveguide which has core width and/or height varied continuously.

Effects of resonant mode coupling on optical Characteristics of InGaN-GaN-AlGaN lasers

Abstract: The phenomenon of resonant mode coupling is modeled and numerically investigated in InGaN-based multiple-quantum-well laser structures. It is shown that under resonant conditions, the internal mode coupling can lead to severe distortions of both near- and far-field characteristics. Taking into account the carrier-induced change of the modal effective index for the lasing mode, we show that the resonant internal mode coupling can result in a strongly nonlinear dependence of the modal gain on injection current, with possible region of negative differential modal gain.

Helical fiber optic mode scrambler

Abstract: The methods and apparatus of the present invention provide advantages for remote laser delivery systems that conduct high levels of light energy through a fiber optic cable to a selectable target surface. Helical fiber optic mode scramblers in accordance with the present invention are an integral portion of a fiber optic cable having a rigid curvature predetermined to advantageously influence the intermodal dispersion characteristics of the fiber optic cable. The various aspects of the present inventions may be employed to increase the useful life of a fiber optic cable, increase the energy throughput of a fiber optics cable, implement smaller sized scramblers, implement more efficient scramblers or to provide for robust implementations that are also easy to assemble. Scrambler assemblies in accordance with the present invention include a support structure and a cylindrical sleeve that work in tandem to maintain to the predetermined spiral curvature of the helical mode scrambler.

Combinatorial polarization scramblers for many-segment PMD emulator

Abstract: In this letter, we present a combinatorial approach to build polarization scramblers in a many-segment polarization-mode dispersion (PMD) emulator. This approach significantly reduces the required number of phase plates and their corresponding controls. It exploits the fact that rotation matrices are noncommutative which gives many different ways of building polarization scramblers out of just a few phase plates. Although these polarization scramblers are correlated, we show, numerically and experimentally, that there is sufficient polarization scrambling between segments to achieve the important key properties of a PMD emulator.

Design of the H10□ to H01○ sector-type mode converter at Ka-band

Abstract: A design procedure for the H10□ to H01° sector-type mode converter at Ka-band is described in detail. As an example, an H10□ to H01° sector-type mode converter with an input rectangular port size as 7.112×3.556 mm2 and another output circular port diameter as 17.2 mm is designed and measured for insertion losses and wanted mode pattern. The mode converting efficiency from H10□ mode to H01° mode is about 91.2%. The insertion losses of the converter are lower than 0.1525 dB with 2GHz band.

Integrated optical mode field adapters at the end of single/multimode fibers

Abstract: In this paper we present the fabrication of optical mode field adaptors for fiber optical communications devices in combination with a new method for spot size measurement for single mode optical components. At the end of standard single mode fibers we have manufactured reproducible mode field transformers with diameters from 5 μm to 90 μm. Additionally, we present a new planar optical field characterization method. BPM simulations are performed to predict the spot sizes at different fiber end diameters. Based on the measurement of a singlemode fiber in accordance with ITU Recommendation G.652 the efficiency is demonstrated and discussed.

Longitudinal mode structure of the two-stage Raman fiber laser

Abstract: We have performed an experimental study of the internal structure of the spectrum arising from the generation of multiple longitudinal modes in a two-stage phosphosilicate Raman fiber laser. The mode structures and their interactions have been studied by the technique of rf beating in the output intensity. It is shown that the mode structure of the first Stokes wave copies the mode structure of the multimode pump laser and the mode structure of the second Stokes wave copies the mode structure of the first Stokes wave. The dependences of the amplitude and width for the rf resonances versus the pump power are discussed.

Frequency tunable light sources and methods of generating frequency-tunable light

Abstract: Frequency-tunable light sources and methods of generating frequency-tunable light are described. In one aspect, a frequency-tunable light source (10) includes a resonant optical cavity (12), an optical gain medium (18), an optical mode filter (20), and a mode frequency tuner (22). The resonant optical cavity (12) supports oscillation of light in at least one longitudinal mode having a respective mode frequency. The optical gain medium (18) is disposed in the resonant optical cavity (12) and is operable to amplify light. The optical mode filter (20) is arranged to intercept light oscillating in the resonant optical cavity (12) and has an optical transmission pass-band with a tunable center frequency. The mode frequency tuner (22) is arranged to intercept light oscillating in the resonant optical cavity (12) and is operable to tunably change the mode frequencies of the at least one longitudinal mode of the resonant optical cavity (12). In another aspect, a resonant optical cavity (12) is provided. The resonant optical cavity (12) supports oscillation of light in at least one longitudinal mode having a respective mode frequency. Light in at least one longitudinal mode in the resonant optical cavity (12) is amplified. The mode frequencies of the resonant optical cavity (12) are changed. The light is transmission band-pass filtered.

Dispersion compensation device

Abstract: The present invention is a dispersion compensation device capable of varying dispersion compensation amount with a simple configuration. The device includes a first mode light conversion section capable of converting input light into light of higher mode, a dispersion compensation section capable of performing dispersion compensation on the higher mode light outputted from the first mode light conversion section corresponding to the status of mode of the higher mode light, a second mode light conversion section capable of converting the light of higher mode dispersion-compensated in the dispersion compensation section into light of original mode, and a mode control section capable of variably controlling the status of mode of the higher mode light converted in the first mode light conversion section, and controlling to convert the higher mode light from the dispersion compensation section to the light of original mode in the second mode light conversion section.

- Ripple-Wall Mode Converters in Circular Waveguide

Abstract: This paper presents the design, numerical analysis, and testing of several symmetric periodic mode converters of two generic types: a uniform ripple-wall converter and a nonuniform ripple-wall converter. All designs operate at a central frequency of 17.136 GHz and convert circular electric modes from one radial mode to the next higher mode. The emphasis of the design study is to maximize the bandwidth of the device without sacri- ficing mode purity. Mode converters from the to mode and from the to mode were investigated in depth, and two designs, each with six periods, were constructed and tested. The nonuniform ripple seems to have a significant advantage over the constant ripple design for the higher mode converter, while the designs for the lower mode converter are comparable. Exper- imental measurements agree well with the theoretical results both in terms of bandwidth and mode content.

Optical communication system and method thereof

Abstract: The present invention discloses an art for eliminating the dependency of the optical modulator on the polarization degree by using an orthogonal mode light which is a mixture of two lights that are perpendicular to each other in polarization direction as a light source. An optical communication system of the present invention comprises: a first optical generator and a second optical generator for generating a first single mode light and a second single mode light, respectively, wherein the first single mode light and the second single mode light are orthogonal and non-interfering with each other, and have the same wavelength; a mixing means for mixing the first single mode light and the second single mode light to output an orthogonal mode light; and an optical modulator for amplifying and modulating the orthogonal mode light after receiving the orthogonal mode light through an optical fiber so as to produce a constantly amplified optical signal regardless of a deflection degree of the orthogonal mode light.

Model for Differential Model Delay Distribution in Multimode Fibers

Abstract: A band-limited fixed frequency linearly polarized optical signal excites several modes of propagation when it is launched into a multi-mode dimensioned optical fiber waveguide. This signal will therefore propagate over multiple paths along the transmission medium resulting in different propagation time for each mode. Thus replicas of the input pulse launched into the multimode fiber arrive at the output at different times, with the fundamental mode arriving first. A Differential Modal Delay (DMD) distribution is thus produced at the output of the fiber. The mode distribution, and consequently the modal delay distribution, are both a function of the physical attributes (geometry, distance, launching angle) of the optical waveguide. In optical communication systems this DMD distribution creates signal distortion that limits system designs (power, modulation, noise) and network performance (reach, rate, capacity). Accurate quantification of this DMD distribution is therefore essential to the prediction and improvement of performance.

A mode converter

Abstract: An in-fiber mode converter comprises fiber portions (10) constituting an input microlens, a fiber portion (20) constituting a phase shifting region adapted to convert a propagation mode of an optical signal into another propagation mode, and fiber portions (30) constituting an output microlens. The fiber portions are spliced, the converter is compact and losses are minimized relative to mode conversion in free space.

Selection of mode num and determination of torsional mode

Abstract: Abstrcat Under seismic action, mode decomposition method is mostly used in seismic response analysis, we can select part modes to represent the whole structure response by using this method .In this paper an effective method is suggested to select proper mode number, additionally, mode directional factor and determination of torsional mode are also mentioned.

Flat optical circuit, design method for wave motion propagating circuit and computer program

Abstract: A planar lightwave circuit is provided which can be easily fabricated by an existing planar-lightwave-circuit fabrication process, which can lower the propagation loss of signal light and which can convert inputted signal light so as to derive desired signal light. A planar lightwave circuit having a core and a clad which are formed on a substrate, has input optical waveguide(s) (111) which inputs signal light, mode coupling part (112) for coupling a fundamental mode of the inputted signal light to a higher-order mode and/or a radiation mode, or mode re-coupling part (113) for re-coupling the higher-order mode and/or the radiation mode to the fundamental mode, and output optical waveguide(s) (114) which outputs signal light. The mode coupling part or the mode re-coupling part is an optical waveguide which has core width and/or height varied continuously.

Fiber optical system and method for synchronized polarization scrambling

Abstract: A fiber optical system (10') for transmitting an optical signal structured into successive FEC frames which repeat at a frame rate (1/τ1) comprises an optical fiber line (1) with at least one, preferably a plurality of successively arranged polarization scramblers (8a to 8c) for polarization modulation of the optical signal transmitted through the optical fiber line (1), and is characterized in that a scrambling rate (1/T sc ) of all of the polarization scramblers (8a to 8c) is equal or almost equal to the frame rate (1/τ1) of the FEC frames. A polarization scrambler and a corresponding method for transmitting an optical signal through the optical fiber line (1).

Mode scrambler using optical fiber wiring board

Abstract: PROBLEM TO BE SOLVED: To manufacture a mode scrambler for multi-mode optical transmission in a small size at low cost SOLUTION: An optical fiber wiring board which has multi-mode optical fibers laid like a circuit on a substrate is used It is preferable that at least two or more wiring patterns for giving a mode scrambling function exist in one board It is preferable that wiring patterns are constituted of circular arcs or cross wiring COPYRIGHT: (C)2005,JPO&NCIPI

Planar lightwave circuit, including an optical branch circuit

Abstract: A planar lightwave circuit is provided which can be easily fabricated by an existing planar-lightwave-circuit fabrication process, which can lower the propagation loss of signal light and which can convert inputted signal light so as to derive desired signal light. A planar lightwave circuit having a core and a clad which are formed on a substrate, has input optical waveguide(s) (111) which inputs signal light, mode coupling part (112) for coupling a fundamental mode of the inputted signal light to a higher-order mode and/or a radiation mode, or mode re-coupling part (113) for re-coupling the higher-order mode and/or the radiation mode to the fundamental mode, and output optical waveguide(s) (114) which outputs signal light. The mode coupling part or the mode re-coupling part is an optical waveguide which has core width and/or height varied continuously.

Frequency-variable light source and method for generating frequency-variable light

Abstract: PROBLEM TO BE SOLVED: To achieve frequency tuning without accompanying mode hopping. SOLUTION: A frequency-variable light source and a method of producing the light source are provided. The frequency-variable light source includes an resonant optical cavity 12, an optical gain medium 18, an optical mode filter 20 and a mode frequency tuner 22. The resonant optical cavity supports oscillation of the light, in at least one longitudinal mode having a corresponding mode frequency. The optical gain medium is disposed in the cavity and amplifies light. The optical mode filter is arranged to intercept the light oscillating in the cavity and has an optical transmission pass-band with a tunable center frequency. The mode frequency tuner is arranged to intercept the oscillating light and changes a mode frequency of the longitudinal mode of the cavity to enable tuning. COPYRIGHT: (C)2006,JPO&NCIPI

Variable optical reflector and strain sensor using multimode fiber Bragg grating and mode conversion

Abstract: We report on a narrow band optical fiber filter utilizing a multimode fiber Bragg grating and fiber mode scrambler in order to tune its reflectivity that is useful as variable optical reflector and strain sensor. A change of reflectivity from 81% to 2% is achieved. We develop a novel fiber Bragg grating strain sensor that allows strain to be applied in the portion of the multimode fiber without grating. Particular advantages of this strain sensor are simple design, low system cost and high sensitivity. A strain sensitivity of 0.0013%/microstrain in change of reflectivity and large dynamic range (0-7,000 microstrain) are demonstrated. The strain sensitivity can be improved greatly by using efficient mode conversion structure in the device.