An explanation of SRS beam cleanup in graded-index fibers and the absence of SRS beam cleanup in step-index fibers

Terry, Nathan B.; Alley, Thomas G.; Russell, Timothy H.

doi:10.1364/oe.15.017509

Cited by 124 publications

(58 citation statements)

References 11 publications

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“…Strikingly, we observed that the entire spectrum accessible to our instruments exhibits a remarkably robust and spatially coherent nonlinear modal profile, in spite of the initially highly multimode excitation [7]. This unexpected Kerr-induced beam self-organization towards a quasi-Gaussian shape is fundamentally different from the spatial beam cleanup of the Stokes wave based on Raman or Brillouin scattering, which was previously reported in the literature [9,10]. Fig.2.…”

Section: Resultssupporting

confidence: 47%

Spatial and spectral nonlinear shaping of multimode waves

Krupa

Tonello

Bendahmane

et al. 2016

2016 IEEE Photonics Conference (IPC)

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Section: Resultssupporting

confidence: 47%

Spatial and spectral nonlinear shaping of multimode waves

Krupa

Tonello

Bendahmane

et al. 2016

2016 IEEE Photonics Conference (IPC)

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“…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.…”

mentioning

confidence: 86%

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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“…While it is well-known that SRS can improve the beam quality in GRIN-MM fibers [19], other multimode fiber structures such as double-clad fibers can be more effective in this regard and even produce single-mode output [20]. We therefore designed and fabricated a double-clad Raman gain fiber (DCRF) and evaluated it in a similar experimental setup.…”

Section: Double-clad Raman Gain Fibermentioning

confidence: 99%

High-Power Continuous-Wave Directly-Diode-Pumped Fiber Raman Lasers

et al. 2015

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We describe novel fiber Raman lasers pumped directly by spectrally combined high power multimode laser diodes at ∼975 nm and emitting at ∼1019 nm. With a commercial multimode graded-index fiber, we reached 20 W of laser output power with a record slope efficiency of 80%. With an in-house double-clad fiber, the beam quality improved to M 2 = 1.9, albeit with lower output power and slope efficiency due to higher fiber loss. We believe this is the first publication of a fiber Raman laser cladding-pumped directly by diodes.

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An explanation of SRS beam cleanup in graded-index fibers and the absence of SRS beam cleanup in step-index fibers

Cited by 124 publications

References 11 publications

Spatial and spectral nonlinear shaping of multimode waves

Spatial and spectral nonlinear shaping of multimode waves

Spatial beam self-cleaning in multimode fibres

High-Power Continuous-Wave Directly-Diode-Pumped Fiber Raman Lasers

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