Experimental realization of femtosecond transverse mode conversion using optically induced transient long-period gratings

Hellwig, Tim; Schnack, Martin; Walbaum, Till; Dobner, Sven; Fallnich, Carsten

doi:10.1364/oe.22.024951

Cited by 22 publications

(11 citation statements)

References 15 publications

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“…In fibres with parabolic index profile, the propagation constants of the modes take equally spaced values, so that coherent mode beating induces a periodic local intensity oscillation along the fibre, which the Kerr effect translates into a periodic longitudinal modulation of the refractive index [4,10,12]. With a simpler two-mode excitation, such type of self-induced or dynamic long-period Bragg grating was previously exploited in [25] for demonstrating light-controlled mode conversion in a GRIN MMF. More generally, four-wave mixing (FWM) interactions involving pairs of beating modes at the same wavelength introduce Bragg-type quasi-phase-matching conditions for a variety of mode coupling processes.…”

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confidence: 99%

Spatial beam self-cleaning in multimode fibres

et al. 2017

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Multimode optical fibres are enjoying a renewed attention, boosted by the urgent need to overcome the current capacity crunch of single-mode fibre systems and by recent advances in multimode complex nonlinear optics [1][2][3][4][5][6][7][8][9][10][11][12][13]. In this work, we demonstrate that standard multimode fibres can be used as ultrafast all-optical tool for transverse beam manipulation of high power laser pulses. Our experimental data show that the Kerr effect in a graded-index multimode fibre is the driving mechanism for overcoming speckle distortions, leading to a somewhat counter-intuitive effect resulting in a spatially clean output beam robust against fibre bending. Our observations demonstrate that nonlinear beam reshaping into the fundamental mode of a multimode fibre can be achieved even in the absence of a dissipative process such as stimulated scattering (Raman or Brillouin) [14,15].Beam propagation in multimode fibres (MMFs) is subject to a complex interplay of spatio-temporal processes. However, only few studies addressed nonlinear pulse propagation in MMFs, leaving this field largely untapped for the past thirty years. Very recently, there has been a resurgence of interest in MMFs for both fundamental and applied research. MMFs could provide a solution to meet increasing demands of new breakthrough technologies for light control and manipulation in communications, high-power fibre lasers and metrology [1,2,16]. In fundamental physics, MMFs may provide a natural tool for investigating spatiotemporal soliton dynamics [5,6], and for unveiling new, exciting nonlinear phenomena [3,4,9,13].It is well known that light experiences an inherent randomization when propagating along MMFs, whereby input laser beams of high spatial quality fade into irregular granularities called speckles. Fibre stress or bending, as well as technological irregularities of the fibre, couple different guided modes and introduce supplementary randomization of the transmission features. For this reason, MMFs are not ideally suited for beam delivery and were replaced by single-mode fibres (SMFs) since the early days of optical communications. Recent works demonstrated that specific signal-processing algorithms could be used to predict or manage the beam shape at the output of a MMF by controlling its input field [17][18][19]. In particular, the application of multiple-input, multiple-output (MIMO) digital signal processing techniques enables the use of spatial-division multiplexing based on MMFs [2]. For high-power beam delivery applications, the spontaneous recovery of spatial beam quality in MMFs has so far been experimentally achieved exclusively through nonlinear dissipative processes such as stimulated Raman scattering (SRS) [14] or stimulated Brillouin scattering (SBS) [20]. However, these techniques do not lead to any self-cleaning of the input laser beam. It is now known that for powers above a critical level (few MWs) self-phase modulation (SPM) may overcome diffraction for any size of the beam, and this may in turn c...

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confidence: 99%

Spatial beam self-cleaning in multimode fibres

et al. 2017

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“…As we move nearer to spatial division multiplexing, another area where multimode fibers may make a difference is in signal processing [33], [34], [125]- [127]. Since intermodal interactions can be controlled with many more degrees of freedom than single mode fiber, and because spatial division multiplexing will require greater signal processing than single-mode transmission, inline signal processing, signal routing, etc.…”

Section: ) Optical Signal Processing and Other Nonlinear Optical Infmentioning

confidence: 99%

Multimode Nonlinear Fiber Optics: Massively Parallel Numerical Solver, Tutorial, and Outlook

Wright

Ziegler

Lushnikov

et al. 2018

IEEE J. Select. Topics Quantum Electron.

155

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Building on the scientific understanding and technological infrastructure of single-mode fibers, multimode fibers are being explored as a means of adding new degrees of freedom to optical technologies such as telecommunications, fiber lasers, imaging, and measurement. Here, starting from a baseline of single-mode nonlinear fiber optics, we introduce the growing topic of multimode nonlinear fiber optics. We demonstrate a new numerical solution method for the system of equations that describes nonlinear multimode propagation, the generalized multimode nonlinear Schrödinger equation. This numerical solver is freely available, implemented in MATLAB ® and includes a number of multimode fiber analysis tools. It features a significant parallel computing speed-up on modern graphical processing units, translating to orders-of-magnitude speed-up over the split-step Fourier method. We demonstrate its use with several examples in graded-and step-index multimode fibers. Finally, we discuss several key open directions and questions, whose answers could have significant scientific and technological impact.

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“…The presence of a dynamic or light-induced long-period grating was previously exploited with short segments of GRIN fiber: these were used as mode couplers, whenever the grating wave vector could compensate for the propagation constants of two signal modes propagating at a different wavelength. 12 In our case, the longitudinal index periodicity provides a quasi-phase matching (QPM) for a special type of spatiotemporal instability, that in normal dispersion regime was dubbed as geometric parametric instability (GPI), to emphasize its origin associated with fiber geometry, as opposed to previously known parametric instabilities, which occur in intrinsically periodic structures.…”

Section: Geometric Parametric Instability Second Harmonic and Supercmentioning

confidence: 99%

Nonlinear dynamics in multimode optical fibers

Wabnitz¹,

Tonello²,

Couderc³

et al. 2018

Quantum Sensing and Nano Electronics and Photonics XV

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We overview recent advances in the research on spatiotemporal beam shaping in nonlinear multimode optical fibers. An intense light beam coupled to a graded index (GRIN) highly multimode fiber undergoes a series of complex nonlinear processes when its power grows larger. Among them, the lowest threshold effect is the Kerr-induced beam self-cleaning, that redistributes most of the beam energy into a robust bell-shaped beam close to the fundamental mode. At higher powers a series of spectral sidebands is generated, thanks to the phase matching induced by the long period grating due to the periodic self-imaging of the beam and the Kerr effect. Subsequently a broadband and spectrally flat supercontinuum is generated, extending from the visible to the mid-infrared.

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Experimental realization of femtosecond transverse mode conversion using optically induced transient long-period gratings

Cited by 22 publications

References 15 publications

Spatial beam self-cleaning in multimode fibres

Spatial beam self-cleaning in multimode fibres

Multimode Nonlinear Fiber Optics: Massively Parallel Numerical Solver, Tutorial, and Outlook

Nonlinear dynamics in multimode optical fibers

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