Showing papers on "Mode scrambler published in 2008"

Ultra‐large effective‐area, higher‐order mode fibers: a new strategy for high‐power lasers

Abstract: This paper describes the physics and properties of a novel optical fiber that would be attractive for building high-power fiber lasers and amplifiers. Instead of propagating light in the fundamental, Gaussian-shaped mode, we describe a fiber in which the signal is forced to travel in a single, desired higher order mode (HOM). This provides for several advantages over the conventional approach, ranging from significantly higher ability to scale mode areas (and hence laser powers) to managing dispersion for ultra-short pulses - a capability that is practically nonexistent in conventional fibers. Particularly interesting is the tact that this approach challenges conventional wisdom, and demonstrates that for applications requiring meter-length fibers (as in high-power lasers), signal stability actually increases with mode order. Using this approach, we demonstrate mode areas exceeding 3200 μm 2 , and propagate signals with negligible mode distortions over up to 50-meter lengths. We describe several pulse propagation experiments in which we test the nonlinear response of this fiber platform, ranging from managing dispersive effects in femtosecond pulse systems, to reducing Brillouin scattering impairments in systems operating with the nanosecond pulses.

Experimental Realisation of 3 × 3 MIMO System with Mode Group Diversity Multiplexing Limited by Modal Noise

Abstract: We show experimentally the feasibility of a 3×3 MIMO system based on Mode Group Diversity Multiplexing over GI-MMF. The main limiting effect of modal noise is reduced by large detection areas.

Optical fiber mode coupling device, having an optimized fiber interface and method of fabrication thereof

Abstract: An optical fiber mode coupling device, capable of being readily connected to a conventional optical fiber with a high degree of ruggedness, is provided. The inventive mode coupling device only allows transmission of at least one supported fiber mode therethrough, and is preferably configured to maximize the coupling, of at least one desired fiber mode, to the at least one supported fiber mode. Advantageously, the inventive mode coupling device is capable of performing the functions of a mode filter for the signal entering its first end, or serving as a mode conditioner for the signal entering its opposite second end. Thus, in one practical application thereof, the novel mode coupling device functions as a mode filter by maximizing the coupling between at least one desired fiber mode of a multi-mode input signal entering the device's first end, and at least one supported mode of the device, to produce an output signal at the device's second end that comprises at least one predetermined fiber mode, corresponding to at least one desired fiber mode. In another practical application thereof, the novel mode coupling device functions as a mode conditioner by maximizing the coupling between an input signal, comprising at least one predetermined fiber mode, that enters the device's second end, and, and at least one supported mode of the device, to produce an output signal at the device's first end that comprises at least one desired fiber mode, corresponding to a conditioned at least one predetermined fiber mode.

Design of a trenched bend insensitive single mode optical fiber using spot size definitions.

Abstract: We have designed a bend insensitive single mode optical fiber with a low-index trench using spot-size definitions and their optimization technique. The bending loss at a 5 mm of bending radius was negligible, while single mode properties were intact.

Modeling of transverse mode interaction in large-mode-area fiber amplifiers.

Abstract: We model the transverse mode interaction in a large-mode-area fiber amplifier by solving the Fresnel wave equation including local gain saturation. In order to calculate the electric field distribution we apply a finite difference beam propagation method, which is followed by the derivation of the modal powers and modal polarization states. A polarization dependent mode amplification is found that is in good agreement with recent experimental results.

Optical fiber mode couplers

Abstract: Described are optical devices and related methods wherein a multiple mode input in a Higher Order Mode (an HOM) optical fiber is converted by a complex mode transformer to produce a fundamental mode output in an optical medium with an E-field that is substantially different than that exiting the HOM optical fiber. The medium is preferably a Large Mode Area (LMA) optical fiber, or free space. The mode transformer may be a series of refractive index perturbations created either by photo-induced gratings or by gratings formed by physical deformations of the optical fiber.

Mode converter based on mode coupling in an asymmetric dual-core photonic crystal fibre

Abstract: A novel mode converter which is realized by mode coupling between a large core and a small core in an asymmetric dual-core photonic crystal fibre is proposed in this paper. The mode indexes of the individual cores are index matched to produce effective mode coupling. Numerical investigations demonstrate that an LP01 to LP02 mode converter with a bandwidth of 14 nm for the loss of 1 dB and polarization-dependent loss lower than 0.14 dB can be realized in a fibre with a length of 12.7 mm.

Contribution to Research on Micro-Lensed Fibers for Modes Coupling

Abstract: In this paper we present a review of different micro-lenses we have developed at the end of single-mode fibers for improving optical coupling efficiency in communication systems. These micro-lenses find their applications in laser-diodes or integrated waveguides to single mode fibers, fiber to detector coupling, or fiber-to-fiber interconnecting. More generally, the applications concern active or passive components to single mode fiber coupling. Three kinds of micro-lenses are considered whose fabrication process has been designed to be very simple and low cost. Some of them are produced by companies in Lannion such as IDIL Fibers Optiques.

Modal sensitivity analysis for single mode operation in large mode area fiber

Abstract: Most of the current large mode area (LMA) fibers are few-moded designs using a large, low numerical aperture (N.A.) core, which promotes mode coupling between core modes and increases bending losses (coupling with claddingmodes), which is undesirable both in terms ofmode area and beamquality. Furthermore, short LMA fiber lengths and small cladding diameters are needed to minimize nonlinear effects and maximize pump absorption respectively in high-power pulsed laser systems. Although gain fiber coiling is a widely used technique to filter-out unwanted modes in LMA fibers, coupling between modes can still occur in component leads and relay fibers. In relay fiber, light coupled into higher-order modes can subsequently be lost in the coiling or continue as higher-order modes, which has the overall effect of reducing the effective transmission of the LP 01 mode and degrading the beam quality. However, maximum transmission of the LP 01 mode is often required in order to have the best possible beam quality (minimal M 2 ). Launching in an LMA fiber with a mode field adapter (MFA) 1 provides an excellent way of ensuring maximum LP 01 coupling, but preservation of this mode requires highmodal stability in the output fiber. Small cladding, low N.A. LMA fibers have the disadvantage of being extremely sensitive to external forces in real-life applications, which is unwanted for systems where highly sensitive mode coupling can occur. In this paper, we present a detailed experimental and theoretical analysis of mode coupling sensitivity in LMA fibers as a function of fiber parameters such as N.A., core diameter and cladding diameter. Furthermore, we present the impact of higher N.A. as a solution to increase mode stability in terms of its effect on peak power, effective mode area and coupling efficiency.

Determination of mode conversion on differential lines

Abstract: This paper describes the problems of mode conversion on differential lines. For the determination of mode conversion between the common mode and the differential mode two possibilities are suggested. The first method is the use of modal impedance matrices Zmacrm to analyse the conversion related to current and voltage. The second method uses the S-parameters to calculate the mixed mode parameters to determine the conversion of modal power waves. Both views on the conversion of modes will be combined to alter the view on the problem.

Mode control for emerging link performance standards

Abstract: A novel mode control device is described, comprising a point-load mode scrambler in tandem with a mode filter. The device may be tuned to ensure compliance of fibre test equipment with new link performance standards. Improvement in the reproducibility of insertion loss measurements on concatenated fibres is demonstrated.

Mode matching for efficient laser diode to single mode fiber coupling

Abstract: This paper presents some analysis for the matching between the elliptical mode field of 1550nm high power laser diode with the circular mode field of the single mode fiber in order to obtain high coupling efficiency with relaxed misalignment tolerances. Three coupling schemes namely Butt, single ball lens and double ball lenses coupling schemes have been employed in pigtailing the butterfly laser diode module using laser welding technique with dual beams from Nd:YAG laser welding system for the attachment of coupling components. The process of fiber attachment to laser diode and welding of various coupling components, such as lens holders, fiber ferrule and welding clips have been performed in what is so called active alignment process, where the system continues measuring the coupled power during the process of coupling and welding of coupling components in their holder to each other and to the main substrate. It has been found that double ball lenses coupling scheme is efficient and more effective for mode matching of highly elliptical (large divergence ratio) laser diode mode field with the circular mode field of a single mode fiber, whereas for small divergence ratios the single ball lens is adequate.

Influence of wavelength and launching condition on frequency response of optical silica fibers

Abstract: In this work, we have studied modal dispersion of silica graded-index optical fibers as a function of mode depending parameters and a lunching condition in local area network (LAN) context. We have investigated mode-depending parameters, namely modal delay, modal attenuation and mode-coupling effects as a function of wavelength. We have proved that the number of excited mode groups depend on spot radius beam when the fiber is excited with a Gaussian input beam. On the other hand, we have demonstrated that we can get a good frequency response of system with a proper wavelength value and under an optimal launching condition in order to decrease the modal dispersion effects of multimode optical fiber.

Low coherent hybrid detection technique for differential mode delay in a multimode optical fiber

Abstract: We present a low coherent hybrid detection technique for the differential model delay (DMD) measurement of a conventional optical multimode fiber with a modified Mach-Zehnder interferometer. A low coherent hybrid detection technique enhances mode coupling between guided modes and the reference mode to easily resolve the modal distribution. An optical spectrum analyzer and a broadband source were used to obtain time-resolved optical beat signals. The measured interference signal was Fourier transformed to obtain time-delay information. A scanning offset launching method was used to excite every available mode in a multimode fiber (MMF). Measurements of a conventional 8-m-long MMF demonstrated the validity of our proposed method. The experimental results of our proposed method agree well with results obtained using a conventional time domain measurement method. Our proposed method can be used to measure the DMD in a short length of optical MMF with a temporal resolution better than 0.72 ps when using an 8-m-long single-mode fiber as a reference.

Optical fiber and mode scrambler equipped with the same

Abstract: PROBLEM TO BE SOLVED: To irradiate a surface to be irradiated with laser beams uniform in irradiation intensity in non-rectangular shape. SOLUTION: The optical fiber includes: a first fiber part F1 having a quartz-made first core 1 whose cross section is formed rectangular of an oblong or square shape and having a first clad 2a which is formed in a manner covering the first core 1; and a second fiber part F2 having a quartz-made second core 11 whose cross section is formed nonrectangular and having a second clad 12 which is formed in a manner covering the second core 11. In the first fiber part F1, the second fiber part F2 is fusion spliced so that a laser beam propagating the first core 1 is made incident on the second core 11. COPYRIGHT: (C)2009,JPO&INPIT

Novel modal delay measurement for higher-order mode fiber using stretched pulse - based interferometry

Abstract: We propose a novel modal delay measurement technique for higher-order mode fiber based on real-time optical frequency-domain reflectometry (OFDR) using an extremely simple, entirely passive and ultrafast wavelength sweeping mechanism, namely dispersion-induced optical pulse stretching.

Theoretical Characterization of a Commercial Large Mode Area - Endlessly Single Mode Photonic Crystal Fiber

Abstract: We report a theoretical characterization of a commercial large mode area endlessly single mode photonic crystal fiber, ie the LMA-15 fiber produced by Crystal Fibre A/S For the study, we employed a finite element leaky mode solver developed in earlier work Based on the computed confinement loss of the modes, we found that as opposed to the claim of the factory, the fiber is obviously multi-moded in the visible light regime, even for a rather long fiber length Additionally, we also computed the dispersion of the fundamental mode which agrees nicely to the measured results given by the factory's datasheet

Dynamic continuously perturbing or vibrating mode scrambler for optical fibres.

Abstract: An apparatus for performing mode scrambling in a multimodal optical fibre during the travel of a beam of electromagnetic radiation or light through the fibre may comprise a device that dynamically delivers a continuous series of differing perturbations to a portion of optical fibre or it may comprise a device that continuously delivers vibrations to a portion of the optical fibre b. The optical fibre system and method for mode scrambling is also specified and the system may comprise an electromagnetic radiation source, an optical fibre, a beam launching means, a perturbing means or a vibrating means. The vibrating means may be an electromechanical transducer 3 coupled to the optical fibre such that when it is driven by a signal generator it vibrates the fibre. If a perturbation means is used it preferably delivers a dynamic series of bends of differing bend radii.

Improvement of the mode quality in large mode area (LMA) fibres

Abstract: We used the offset launch and the near field imaging technique to analyse the modal content of large mode area (LMA) fibres in different launch conditions. The coiling technique was applied to suppress higher order mode contents in order to estimate the modal power distribution and to verify the loss factor for the single modes. Based on this analysis, an optimised coiling for LMA fibres will be developed, to suppress the higher order mode contents while maintaining the highest possible fundamental mode content.