Showing papers on "Mode scrambler published in 2010"

Holographic mode field generation for a multimode fiber channel

Abstract: For a conventional launch into an MMF, a large number of modes are excited, entailing significant modal dispersion and limiting the bandwidth of the MMF link. To mitigate modal dispersion in MMF, a new single mode field generation technique using a transmissive spatial light modulator and a set of lenses is proposed and demonstrated experimentally. The rapid reconfiguration speed of the SLM surmounts the mode switching limitations of previous single mode field generation techniques while allowing for adaptive updating of the incident field on the MMF. For modes up to azimuthal and radial mode numbers of 4, the generated modal electric fields achieved high power coupling efficiencies, in the range of 90.15% to 95.79%.

Adiabatic Mode Conversion in Multimode Waveguides Using Chirped Computer-Generated Planar Holograms

Abstract: We discuss the design of a mode converter based on optical analogy of adiabatic passage via a level crossing in multimode waveguides. Computer-generated planar holograms are used to implement the chirped gratings that mimic the laser excitation used in the transfer between quantum states of atoms and molecules. The mode coupling properties are analyzed using the coupled mode theory and shown to resemble the level crossing process. Key features of the devices are illustrated with theoretical calculations and numerical examples. The proposed mode converter shows a bandwidth in excess of 300 nm in the optical communications band.

Stable coherent MIMO transport over few mode fiber enabled by an adiabatic mode splitter

Abstract: Simulations confirm stable MIMO transport of three channels over a two mode fiber — even in the presence of fiber bending induced mode coupling — enabled by a new adiabatic mode splitter output coupler.

Mode division multiplex communication technique based on dynamic volume hologram and phase conjugation

Abstract: We propose mode division multiplex communication technique that can split a specific spatial mode in light from a spatial mode multiplexed in an optical fiber by fusion of a phase conjugation technique with spatial filtering processing by multiplexed volume holograms and random diffusers. In mode division multiplexing, the optical signal outgoing from the multimode optical fiber is in a condition that optical inform ation of plural spatial modes is overlapped, therefore it is difficult to de-multiplex electrically after light detection. Our technique enables to split it into each mode all optically and to compensate temporal modal shift dynamically. Mode de-multiplexing is realized by multiplexed holographic arithmetic device and phase matching of a wave surface for the spatial mode orthogonal to time. Therefore, if we use indices in conventional electronic processing, a very high-speed operation equivalent to that of 10-100PFLOPS can be realized without causing any delay in light information to be transmitted. Moreover, it can realize constructions of a system that can dynamically respond to temporal mode variations and distortions with fiber transmissions by using a photorefractive medium. Separating of around 60-70% was ach ieved in an experiment of separating three multiplexed spatial modes by controlling a volume type dynamic reconfigurable device based on LiNbO

Design of a single-polarization single-mode photonic crystal fiber with a near-Gaussian mode field and wide bandwidth

Abstract: Single-polarization single-mode (SPSM) fiber can efficiently eliminate polarization mode coupling, polarization mode dispersion, and polarization-dependent loss. Up to now, most single-polarization fibers have been designed based on form birefringence, which would result in a non-Gaussian field distribution and a small effective mode field area. In this paper, a novel structure of SPSM photonic crystal fibers based on the resonant coupling phenomena is proposed and analyzed by using a full-vector finite-element method with a second-order transparent boundary condition. From the numerical results it is confirmed that this fiber has a near-Gaussian mode field within the wavelength range from 1.46 to 2.2μm, where only one polarized mode exists effectively, and the mode field area is about 79μm2 at the wavelength of 1.55μm, matching that of the conventional single-mode fiber.

Modal Dispersion Mitigation in Standard Single-Mode Fibers at 850 nm With Fiber Mode Filters

Abstract: We investigate the possibility of using a fiber which supports only the fundamental LP01 mode at 850 nm as a mode filter to overcome modal dispersion in standard single-mode fiber links that employ either multitransverse or single-transverse-mode vertical-cavity surface-emitting lasers. The individual power penalties due to modal noise and modal crosstalk effects in the link are investigated.

A novel cylindrical TE2,1 mode converter

Abstract: A novel, compact arrangement for Ka-band mode couplers, which convert a rectangular waveguide TE1,0 to cylindrical waveguide TE2,1 mode, has been designed, constructed, and tested The design features a set of longitudinal slots, positioned in regions of negligible current flow for the TE2,1 mode, allowing its propagation to be preferentially favored, by suppression of the fundamental TE1,1 mode Numerical simulations and experimental measurements display good agreement, showing transmission of the intended TE2,1 mode at levels of better than −5 dB, from a frequency of ∼375 to 41 GHz Subsequent farfield measurements confirm the presence of the TE2,1 mode, demonstrating good agreement when compared with analytical expectations Such a device would be an ideal candidate for an application where mode purity, bandwidth, and ease of construction are of primary importance and where the transmission efficiency is of limited concern

Modeling of large flattened mode area fiber lasers

Abstract: Potentialities of independent tailoring the index and gain profiles in fiber laser aiming to achieve a strong modal discrimination are theoretically examined. It is demonstrated by numerical simulations existence of fiber amplifier constructions which have the flattened fundamental mode profile in the gain region. It is shown that the fundamental mode retain the largest modal gain in comparison with modal gains of higher-order-modes for any depletion of the gain by the fundamental mode. The particular design is presented with the flattened fundamental mode area 6360 μm squared.

Improvement of Coiling Mode to Suppress Higher-Order-Modes by Considering Mode Coupling for Large-Mode-Area Fiber Laser

Abstract: Mode coupling, bend distortion and bend loss are important considerations in large mode area (LMA) fiber laser. Both mode coupling and mode distortion were studied in the step-index fiber in theory. The dependence of mode power on propagation distance, effective bend radius was calculated with the bend radius changing suddenly and gradually. Taking mode coupling into account, we designed a new cone-shaped coiling device for beam quality improvement. These results and design are of benefit to the applications of coiling fiber to improve beam quality for LMA fiber laser.

Laser oscillator and filtering method

Abstract: Provided is a fiber laser including a mode filter for selectively attenuating, among modes included in laser light propagating through a multi-mode fiber, any mode other than a radially polarized mode. Among the modes included in the laser light propagating through the multi-mode fiber, the fiber laser causes the radially polarized mode to resonate, so as to emit radially polarized laser light. The mode filter includes a long-period fiber grating obtained by writing, to a multi-mode fiber capable of guiding the radially polarized mode, a grating for selectively attenuating any waveguide mode other than the radially polarized mode.

Simple suppression technique for higher-order mode amplification in bent large mode area triple-cladding fibers

Abstract: A novel technique to suppress the higher-order mode in bent LMA triple-cladding fibers is proposed. It is shown that the higher-order mode can be coupled to a cladding mode with only an adjustment of the bending diameter.

Transmission power control method and transmission power control device

Abstract: Disclosed is a method for achieving highly accurate transmission power control of a power amplifier when switching the power amplifier between the compressed mode and the uncompressed mode. The method comprises: when switching from a first mode to a second mode, determining, as a comparison reference value error, the output power error in the first mode relative to the power setting value for the first mode (Step ST32); setting the power setting value for the second mode so as to cancel out the output power error between the two modes (Step ST33); determining the output power error in the second mode relative to the power setting value for the second mode (Step ST35); determining the gain linearity value on the basis of the power setting value for the second mode and the output power error in the second mode (Step ST36); and, on the basis of the gain linearity value, resetting the power setting value for the second mode so as to cancel out the comparison reference value error in the first mode and the output power error in the second mode (Steps ST37, 38).

Simple and Reliable Evaluation Method of Multi-Mode Polymer Optical Waveguides

Abstract: Polymer optical chip containing a combination of 45°-angled cut waveguide, Y-splitter and S-bend structures was designed and fabricated for simple and reliable evaluation of multi-mode waveguides. Effect of mode scramblers was investigated as an appropriate input condition for standardization of measurement of optical characteristics of multi-mode waveguides.

Fabrication of large flattened mode optical fiber for high power laser

Abstract: Large flattened mode optical fiber with raised index ring around the outer edge of the fiber core has been fabricated through modified chemical vapour deposition process to raise the threshold for non-linear interaction in high power laser fiber. The conversion of the fundamental mode shape from a Bessel function to a top hat function, enhances the effective area of the core intersected by the mode without increasing the physical size of the core. The shape of the fundamental mode is observed to be strongly dependent on the width of the raised index ring from the modal analysis. Suitable fiber parameters have also been estimated through the modal field analysis. Fabrication process steps have been optimized to achieve the desired fiber parameters. Modal field distribution, transmission properties and bending loss of the fabricated fibers have been characterized.