Self-organized instability in graded-index multimode fibres

Wright, Logan G.; Liu, Zhanwei; Nolan, Daniel A.; Li, Mingjun; Christodoulides, Demetrios N.; Wise, Frank W.

doi:10.1038/nphoton.2016.227

Cited by 226 publications

(158 citation statements)

References 55 publications

(113 reference statements)

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confidence: 88%

“…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].…”

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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

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“…Multimode optical solitons [9], dispersive waves [10], geometrical parametric instabilities [11], spatial beam cleaning [12] and ultra-wide supercontinuum [13,14] may be counted among the major experimental advances reported over the last couple of years only. In particular, several papers have recently reported nonlinear beam reshaping and selfcleaning effects in multimode optical fibers with a parabolic refractive index profile (known as graded index or GRIN fibers) [11][12][13][14][15][16]. With these highly multimode fibers, light that is delivered as a random speckled beam at low powers was observed to evolve into a cleaned, almost Gaussian shaped beam at high power levels.…”

Section: Introductionmentioning

confidence: 99%

“…A theoretical explanation of the mechanism leading to the Kerr self-cleaning phenomenon is not yet completely clear, even though it can be well reproduced by means of the numerical integration of the (2 + 1 + 1) nonlinear Schrödinger (NLS) (or Gross-Pitaievski) propagation equation. The condensation of optical waves [6], as well as the nonlinear nonreciprocity of nonlinear mode coupling [12], and self-organized instability [15], have been proposed as possible mechanisms at play in the observed self-cleaning behavior. Beam self-cleaning was experimentally obtained in various experimental configurations involving different pump lasers, mostly at the 1 micrometer wavelength in the normal dispersion regime, with pulse durations ranging from femtoseconds [16] to nanoseconds [12], and with optical fibers of different diameters and from different manufacturers.…”

Section: Introductionmentioning

confidence: 99%

Kerr self-cleaning of pulsed beam in an ytterbium doped multimode fiber

Guenard¹,

Krupa²,

Dupiol³

et al. 2017

Opt. Express

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We experimentally demonstrate that Kerr spatial self-cleaning of a pulsed beam can be obtained in an amplifying multimode optical fiber. An input peak power of 500 W only was sufficient to produce a quasi-single-mode emission from the double-clad ytterbium doped multimode fiber (YMMF) with non-parabolic refractive index profile. We compare the self-cleaning behavior observed in the same fiber with loss and with gain. Laser gain introduces new opportunities to achieve spatial self-cleaning of light in multimode fibers at a relatively low power threshold.

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“…Quite remarkably, experiments of [7] revealed that the Kerr selfcleaning of the pump beam is frequency transferred across the entire spectrum of the GPI sidebands. Finally, for higher powers and fiber lengths, the GPI sidebands merge into a broadband SC as a result of the interplay of the Kerr effect and Raman scattering, and both effects cooperate with each other in reinforcing the wideband spatial beam cleaning [8,9,14,15]. In particular, the dependence of SC generation on a GRIN MMF as a function of pump power was experimentally studied in [8,15].…”

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Spatiotemporal characterization of supercontinuum extending from the visible to the mid-infrared in a multimode graded-index optical fiber

et al. 2016

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We experimentally demonstrate that pumping a gradedindex multimode fiber with sub-ns pulses from a microchip Nd:YAG laser leads to spectrally flat supercontinuum generation with a uniform bell-shaped spatial beam profile extending from the visible to the mid-infrared at 2500 nm. We study the development of the supercontinuum along the multimode fiber by the cut-back method, which permits us to analyze the competition between the Kerr-induced geometric parametric instability and stimulated Raman scattering. We also performed a spectrally resolved temporal analysis of the supercontinuum emission. The strong modal confinement and the versatile dispersion engineering of single-mode fibers (SMFs) have permitted to demonstrate efficient and spatially coherent supercontinuum (SC) sources spanning from the ultra-violet to the mid-infrared (MIR) [1]. However, the small mode area of SMFs limits the accepted energy to relatively low values (less than 20 μJ for subns pulses). For this reason, SC sources based on SMFs cannot be used for applications where high pulse energies are required. Although multimode fibers (MMFs), such as graded-index (GRIN) fibers, permit the propagation of high energy pulses, these are subject to mode beating and mixing, owing to the difference of modal propagation constants and linear mode coupling. Modal interference brings a speckled intensity pattern at the MMF output, which prevents the use of MMFs whenever the preservation of spatial beam quality is required [2].Recent experiments by Krupa et al. [3] led to the unexpected discovery that Kerr nonlinearity of glass fibers above a certain threshold pulse power may lead to the generation of a selfsustained bell-shaped nonlinear beam in a highly multimode GRIN fiber. This means that linear mode mixing can be effectively washed out by means of the Kerr effect, so that a cleaned multimode light beam remains effectively selfpreserved. Kerr self-cleaning (KSC) stems from nonlinear coupling among the fundamental mode and higher-order modes [3,4]. KSC occurs at power levels at least one order of magnitude lower than the critical power of catastrophic light self-focusing in a GRIN MMF [5]. Because it is a conservative process, KSC is fundamentally different from the well-known Raman beam cleanup that is observed at the Stokes wavelength [6]. In addition, KSC occurs before a substantial pump spectral broadening has occurred [3]. For powers above the KSC threshold, nonlinear spectral broadening in MMFs results from a complex interplay between the spatial and temporal degrees of freedom [7][8][9]. Because of the self-imaging of the multimode beams in a GRIN MMF, the Kerr effect leads to a long-period intensity grating which induces mode conversion [4] and quasi-phase-matched (QPM) four-wave mixing (FWM) [10]. For temporal multimode femtosecond solitons in the anomalous dispersion regime [11], the nonlinear index grating produces an effective periodic nonlinearity which, in turn, induces a series of dispersive wave sidebands [12,13]. On the other hand, for ...

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Self-organized instability in graded-index multimode fibres

Cited by 226 publications

References 55 publications

Spatial beam self-cleaning in multimode fibres

Spatial beam self-cleaning in multimode fibres

Kerr self-cleaning of pulsed beam in an ytterbium doped multimode fiber

Spatiotemporal characterization of supercontinuum extending from the visible to the mid-infrared in a multimode graded-index optical fiber

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