Showing papers on "Mode scrambler published in 2002"

High performance fused-type mode-selective coupler using elliptical core two-mode fiber at 1550 nm

Abstract: In this letter, we demonstrate a high performance fused-type mode selective coupler that couples the LP/sub 11/ mode in one fiber and the LP/sub 01/ mode in another using highly elliptical core two-mode fibers. The phase-matching condition was achieved by etching and prepulling portions of two-mode fibers. The coupling efficiency and the mode extinction ratio of 56% to 80% and 22-32 dB, respectively, were achieved with high temperature stability over 1515- to 1595-nm wavelength range.

Novel mode converter based on hollow optical fiber for Gigabit LAN communication

Abstract: A novel mode converter based on a hollow optical fiber is proposed to reduce the differential modal delay penalty in optical transmission over multimode fibers (MMFs). The device adiabatically converts a fundamental mode in a single-mode fiber to a ring-shaped mode in order to excite selectively a set of higher order modes with a similar group velocity in MMF, maintaining center-launching configuration. The mode converter is composed of serially concatenated concentric segments of a single-mode, hollow, and multimode optical fiber. For 2.5-Gb/s transmission over 500-m-long MMF using a laser diode transmitter, the proposed mode converter shows improvement in bit-error-rate performance at both wavelengths of 1.31 and 1.55 /spl mu/m.

Simulation-based prediction of multimode fiber bandwidth for 10 Gb/s systems

Abstract: The recent wide-spread deployment of gigabit, multimode, optical data links has led to the need for better design methodologies to both lower cost and improve performance. One of the most critical performance predictors for these systems is the bandwidth of the multimode fiber used in the link. We have demonstrated, through an integrated device/system simulation environment, that an empirical differential-mode delay-based method for predicting modal bandwidth can be accurate to within a few percent of the more rigorous index-based method.

Polarization scrambler unit and multi-repeater transmission system incorporating the same

Abstract: The present invention minimizes trouble and loss caused by a failure polarization scrambler. A polarization scrambler unit 201 of the invention is provided with: two polarization scramblers 2 - 1 and 2 - 1 ; a switching unit for coupling either one of the polarization scramblers 2 - 1 and 2 - 1 to a transmission line fiber 4 ; a detection unit for detecting an output signal from the polarization scrambler 2 - 1 (or the polarization scrambler 2 - 2 ) coupled to the transmission line fiber 4 ; and a controlling unit for switching, via the switching unit, between the polarization scramblers 2 - 1 and 2 - 2 whenever a false output signal is detected by the detection unit. Thus, the polarization scrambler unit 201 has a redundant structure.

Optical waveguides and optical devices with optical waveguides

Abstract: The invention provides an optical waveguide for enabling the reduction of a coupling loss caused by difference in the size of a mode field diameter between optical waveguide modes different in the mode field diameter and a coupling loss caused by reflection on a boundary caused by the difference of media and an optical device using it. Structure provided with a mode field diameter converter provided with an antireflection part required to reduce a coupling loss between a microoptical circuit and a single mode optical fiber is integrally produced using effective refractive index control based upon photonic crystal structure.

Optical waveguide exhibiting strongly positive dispersion, and system utilizing same

Abstract: An optical waveguide designed to generate positive dispersion when operated in a high order mode. The optical waveguide in one embodiment is designed to generate positive dispersion slope, in another embodiment to generate negative dispersion slope and in yet another embodiment nominally zero dispersion slope. In one embodiment the high order mode is the LP02 mode and in another embodiment the high order mode is the LP03 mode. In another embodiment the optical waveguide is a few mode fiber. In an exemplary embodiment the optical waveguide is used in combination with a mode transformer, such as a transverse mode transformer to achieve the desired high order mode.

Fiber optical attenuator

Abstract: A fiber optical attenuator utilizing the cut-off phenomenon for single mode propagation of an optical wave down a single mode fiber, comprising an element such as a pixelated liquid crystal element, capable of spatially changing the phase across the cross section of an input optical signal. Such a spatial phase change is equivalent to a change in the mode structure of the propagating wave. The signal propagating in the single mode output fiber is attenuated in accordance with the extent to which higher order modes are mixed into the low order mode originally present. When the mode is completely transformed to higher order modes, the wave is effectively completely blocked from entering the output single-mode fiber, and the attenuation is high. The level of attenuation is determined by the fraction of the wave which is converted to modes other than the lowest order mode, and is thus controllable by the voltage applied to the pixels of the liquid crystal element.

On the dynamics of polarization mode dispersion

Abstract: The PMD dynamics in aerial fiber can be well modeled by highly mode coupled wave-plates via the mode coupling angle fluctuation described by a Gaussian probability transition function. The RMS mode orientation angle undergoes a Brownian motion in aerial fiber. The fitting parameter K is easily measured and used as a single quantity to describe the dynamical nature of a field optical fiber with sufficient statistics. This allows industry to measure and quantify SOP and PMD correlation when field testing optical fibers. We find the K value for aerial fiber is about an order of magnitude larger than that of the buried fiber.

Bistable liquid crystal device having two drive modes

Abstract: A twisted nematic bistable liquid crystal (2) switching between two stable states in a high voltage mode is used in an AMLCD low voltage drive. The picture electrodes (14) and the counter electrode (15) are part of an active matrix, enabling the display to be used also in a fast video mode. Thus, a bistable liquid crystal display device is provided which has two drive modes, a low frequency mode, (first drive mode, also called “bistable mode”, “passive mode” or “high voltage mode”) for applications requiring slower switching times and lower power consumption and a high frequency mode (second drive mode, also called “active mode, “active matrix drive mode” or “fast video mode”) for grey scale images and video applications.

All-fiber wavelength- and mode-selective coupler for optical interconnections

Abstract: We experimentally demonstrate a new wavelength- and mode-selective coupler utilizing intermodal coupling between a standard single-mode fiber (SMF) and a hollow optical fiber (HOF). The fabricated device routes optical signals such that a 1.3‐µm signal is directed to the HOF port, adiabatically converting the LP01 mode into a ring-shaped mode, which can be further connected to a gigabit ethernet link, reducing the differential mode-dispersion penalty. Optical signals near 1.5 µm, meanwhile, stay in the LP01 mode of the SMF arm for further connection to conventional wavelength-division multiplexing links based on erbium-doped fiber amplifiers. The performance of the device is characterized in terms of insertion loss, channel isolation, and mode-conversion efficiency.

Tension-tuned acousto-optic bandpass filter

Abstract: Device whereby one or more bands of optical wavelengths may be selected for further transmission. All light within the optical bandwidth of operation is first coupled from the core mode of an optical fiber to a specific cladding mode by a chirped broadband cladding mode coupler. These cladding mode lightwaves then enter a narrow-band core mode coupler whereby selected optical bands of wavelengths, tuned by the tension on the optical fiber, are re-coupled back into the core of the optical fiber. The chirped broadband cladding mode coupler is isolated from the narrow-band core mode coupler by an acoustic absorber to limit the acoustic interaction between them.

Recording and playback apparatus and optical head

Abstract: The light intensity of a light beam emitted from a light source is appropriately controlled when the light beam is transmitted through a variable optical coupling efficiency device in an optical head. During a read mode, the light beam from the light source is incident on an optical disk at an intensity relatively weaker than that of the light source. By switching the optical coupling efficiency of the variable optical coupling efficiency device between a write mode and a read mode, the light intensity directed to an optical recording medium is substantially varied from the write mode to the read mode. This arrangement eliminates the need for substantially increasing the optical output power ratio of the light source of write power to read power.

Fiber tail assembly with optical signal tap

Abstract: A method and optical tap is provided for forming a monitor signal that is a measure of optical power in a guided mode output of an optical modulator. The method and optical tap may monitor the guided mode power without tapping the guided mode light, even when optical power of the radiation modes is non-complementary to that of the output mode. Light from the radiation modes of the optical modulator is coupled into the wall of a capillary through a front face. Separate portions of the radiation mode light are reflected into photodetectors, which form photocurrents that are incoherently added to form the monitor signal.

Selective mode excitation by nonaxial evanescent coupling for bandwidth enhancement of multimode fiber links

Abstract: We present an analysis of conditioned launch in a gradient- index multimode fiber (MMF). Selective mode excitation is obtained by nonaxial evanescent coupling between two highly asymmetric side- polished fibers: a single-mode fiber and an MMF with an exposed core. An index-matching slab improves the coupling efficiency and selectivity. The simulation shows that about 40% of modes, only high-order modes, are excited in the MMF. When compared to an overfilled launch, the bandwidth of a perturbed index fiber is enhanced more than twofold for large parameter variations.

Mode coupling devices with complex spectral profile

Abstract: A mode coupling device is provided for coupling co-propagating modes in an optical waveguide to provide a gain flattening filter for use with an optical amplifier such as an erbium-doped fiber amplifier. The mode coupling device includes a plurality of long period grating sections having equal spatial periods, with adjacent grating sections separated by an interval of less than 10 periods in length. Also provided is a method for manufacturing the mode coupling device, including a method for determining the parameters of the device and a method for fine tuning the device to provide a loss spectrum closely matching the output spectrum of the optical amplifier. The mode coupling device is useful for flattening the gain of the optical amplifier.

Optical band pass filter using long-period grating

Abstract: PROBLEM TO BE SOLVED: To provide an optical filter having a new structure and using a long- period grating (LPG) so as to provide in-line band pass filtering for light signals. SOLUTION: In the basic aspect, two LPGs not similar to each other are mounted on an optical fiber transmission line. The first LPG converts the light transmitted in the basic mode or LP01 mode of the optical fiber transmission line into a higher order mode (HOM) of the optical fiber in a wide wavelength range. The signals with converted mode have the mode LPm ,n and then coupled to a second waveguide having different transmission characteristics from those of the first waveguide. The propagation of light in the LPm ,n mode is supported by the second waveguide. The light having the converted mode is transmitted through the second LPG. The signals in a narrow band with selected wavelengths received by the second LPG are again converted into the LP01 mode. The selected narrow band of the LP01 mode efficiently propagates on the rest of the optical fiber transmission line.

Single mode operation of a curved-mirror vertical-emitting laser with an active distributed Bragg reflector

Abstract: Stable single transverse mode operation is achieved from curved-mirror vertical-emitting lasers at 850 nm. By including gain-producing layers inside the bottom distributed Bragg reflector (DBR), we remove unnecessary multi-cavity effect. With continuous wave optical pumping at 663 nm, single mode power up to 7 mW is observed at room temperature. When pumped near the center of the curved mirror made of optical epoxy, the device operates in a single transverse mode reliably. The diameter of the fundamental mode is generally larger than 10 µm. As the pump position moves away from the center, lasing from higher-order modes is observed.

High functionality mode transformers with bandwidth control and mode selectivity

Abstract: We propose high functionality field transformation in irregular rectangular waveguide structures. Multiresolution optimization allows good convergence and a stepped wall profile provides for a large number of degrees of freedom. The resulting structures are compact, with dimension of a few wavelengths, and can have functionality not achievable through periodic means. For illustration, we have designed frequency-dependent mode converters, mode-selective reflectors, and multiple mode converters, where more than one mode is converted simultaneously, all with virtually 100% efficiency. Non-uniqueness affords design selection based on the frequency response.

Mode distribution and bandwidth characteristic of arbitrarily trapezoidal-groove guide for millimeter waves

Abstract: The modes TE and TM of arbitrarily trapezoidal-groove guide are analyzed by using the mode-matching method. The mode TE11 is the dominant mode of the trapezoidal-groove guide under different conditions. The bandwidth characteristic and the operation condition for the single dominant mode are discussed. The obtained conclusions are of very important significance in theoretical study and practical application of trapeziodal-groove guides for millimeter waves.

Mode coupling in plastic optical fiber

Abstract: This paper presents a theoretical investigation on the mode coupling and mode coupling induced attenuation in step-index plastic optical fiber under different launching condition. We solved numerically power flow equation of multimode optical fiber by explicit finite difference methods. In our calculation, we adopted mode coupling coefficient measured in Garito’s experiments , and supposed power distribution of incident beam have Gaussin form with respect to angle between beam and optical core axis. Under different incident angle and same beam width, we calculated power distribution at fiber output end when optical fiber length is 1,5,15, 20, 50m respectively. In shorter transmission distance, mode coupling isn’t evident, output power distribution is similar to input ones. With increasing of fiber length, power diffused gradually from high order modes to low order modes, and mode coupling finished in about 20m, where equilibrium mode distribution is achieved. In addition, we calculated mode-coupling induced attenuation of different width and launching angle Gaussin beam, with enhancing of beam width and launching angle , attenuation increased .

Starting mode regime in an FEM oscillator with a Bragg resonator

Abstract: In an FEM oscillator with a Bragg resonator excitation of an additional starting mode can be exploited as a source of an initial signal for the operating mode. In such a regime the starting mode has a rather small detuning from synchronism resulting in a high temporal gain but a rather small electron efficiency. With the starting mode growth the situation becomes favorable for excitation of the operating mode. Afterwards due to a non-linear competition mechanism the operating mode suppresses the starting mode and a single-mode regime of oscillations is realized with a rather high efficiency.

Challenging the notion of equal modal power distribution in multimode optical fibers

Abstract: In this paper we report both theoretical and experimental evidence that equal MPD is extremely unlikely in few mode fiber, and next to impossible to achieve in highly multimode fiber. In one approach, we simply add together the intensity distributions of the various possible modes for a given V number fiber, and compare with what is observed in the laboratory under a variety of conditions. This is done for the incoherent case using a one hundred meter length of a similar fiber. In another method, Gloge's theory for the number of propagating modes is used to determine the approximate MPD in a highly multimode fiber. Both techniques point to the conclusion that the most likely distribution of power among the modes is one that decreases exponentially with mode, despite various mode-scrambling efforts.

Characterization of the interference coupling technique into single mode fibers

Abstract: Summary from only given. We propose a comparison of the single beam and the interference coupling schemes into single mode fibers. Coupling efficiency calculations, based on the overlapping integrals of the fiber mode field and the distribution of the input fight intensity are presented. This study takes into account the light coupling and propagation in the fiber core and cladding.

Permanent laser induced birefringence using red light in optical fibers

Abstract: Summary form only given. Polarization mode coupling in birefringent fibers is well understood using coupled-mode theory. The couplers can be fabricated by modifying the birefringence of the fiber through internal or external exposure to laser light. We report, for the first time, on polarization mode couplers written into a single mode Andrew E-core fiber.