Spatial beam self-cleaning in multimode fibres

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 [1-13]. 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 …

Nonlinear beam self-cleaning in a coupled cavity composite laser based on multimode fiber

International audience; We study a coupled cavity laser configuration where a passively Q-switched Nd:YAG microchip laser is combined with an extended cavity, including a doped multimode fiber. For appropriate coupling levels with the extended cavity, we observed that beam self-cleaning was induced in the multimode fiber thanks to nonlinear modal coupling, leading to a quasi-single mode laser output. In the regime of beam self-cleaning, laser pulse duration was reduced from 525 to 225 ps. We also observed a Q-switched mode-locked operation, where spatial self-cleaning was accompanied by far-detuned nonlinear frequency conversion in the active multimode fiber.

Optimization of wavelength division multiplexing in N×160Gbit/s terrestrial transmission systems

Abstract We analyze, from an engineering viewpoint, the prospects of an exploitable upgrade of terrestrial fiber systems based on standard monomode fiber and dispersion compensating units, for future N  × 160 Gbit/s transmission systems. We show that dispersion swing, average dispersion and input pulse power are the key parameters that govern the system performances. We show that whenever the dispersion swing is arranged in a symmetrical setup and the compensation ratio is optimized accordingly, one may obtain a significant improvement of the transmission performances.

Modal attraction on low order modes by Kerr effect in a graded refractive index multimode fiber

Modal attraction towards low order modes in a GRIN multimode fiber was experimentally observed at high power and characterized, thus enriching the dynamics of the Kerr self-cleaning effect leading to quasi fundamental mode generation.

Observation of Geometric Parametric Instability Induced by the Periodic Spatial Self-Imaging of Multimode Waves

Spatio-temporal mode coupling in highly multimode physical systems permits new routes for exploring complex instabilities and forming coherent wave structures. We present here the first experimental demonstration of multiple geometric parametric instability sidebands, generated in the frequency domain through resonant space-time coupling, owing to the natural periodic spatial self-imaging of a multimode quasi-continuous-wave beam in a standard graded-index multimode fiber. The input beam was launched in the fiber by means of an amplified microchip laser emitting sub-nanosecond pulses at 1064 nm. The experimentally observed frequency spacing among sidebands agrees well with analytical predic…

Spatial and spectral nonlinear shaping of multimode waves

We demonstrate a novel nonlinear dynamics of multimode fibers that reshapes their spectral and spatial beam profiles, based on spatiotemporal modulation instability. Sidebands ranging from the visible to the near-infrared are carried by one and the same spatial bell-shaped profile.

Spatiotemporal Dynamics in Multimode Nonlinear Optical Fibers

International audience

Robustness of 40 Gb/s ASK modulation formats in the practical system infrastructure.

In this work, we analyzed by means of numerical and laboratory experiments the resilience of 40 Gb/s amplitude shift keying modulation formats to transmission impairments in standard single-mode fiber lines as well as to optical filtering introduced by the optical add/drop multiplexer cascade. Our study is a pre-requisite to assess the implementation of cost-effective 40 Gb/s modulation technology in next generation high bit-rate robust optical transport networks. © 2006 Optical Society of America.

Multidimensional shaping of spatiotemporal waves in multimode nonlinear fibers

Recent experiments have shown that nonlinear wave propagation in multimode optical fibers leads to complex spatio-temporal phenomena. In this talk, we introduce new approaches for the control and optimization of nonlinear beam reshaping in the spatial, temporal and spectral dimensions. The first approach applies to spatial beam self-cleaning the technique of transverse wavefront shaping, which permits to launch an optimized input mode combination, that results in the stable generation of a whole nonlinear mode alphabet at the fiber output. The second approach introduces a longitudinal tapering of the core diameter of multimode active and passive fibers, which permits to generate ultra-wideb…

Spatiotemporal light-beam compression from nonlinear mode coupling

We experimentally demonstrate simultaneous spatial and temporal compression in the propagation of light pulses in multimode nonlinear optical fibers. We reveal that the spatial beam self-cleaning recently discovered in graded-index multimode fibers is accompanied by significant temporal reshaping and up to four-fold shortening of the injected sub-nanosecond laser pulses. Since the nonlinear coupling among the modes strongly depends on the instantaneous power, we explore the entire range of the nonlinear dynamics with a single optical pulse, where the optical power is continuously varied across the pulse profile.

Spatiotemporal Nonlinear Interactions in Multimode Fibers (invited)

International audience

Seeded intermodal four-wave mixing in a highly multimode fiber

International audience; We experimentally and theoretically investigate the process of seeded intermodal four-wave mixing in a graded-index multimode fiber, pumped in the normal dispersion regime. By using a fiber with a 100-mu m core diameter, we generate a parametric sideband in the C-band (1530-1565 nm), hence allowing the use of an erbium-based laser to seed the mixing process. To limit nonlinear coupling between the pump and the seed to low-order fiber modes, the waist diameter of the pump beam is properly adjusted. We observe that the superimposed seed stimulates the generation of new spectral sidebands. A detailed characterization of the spectral and spatial properties of these sideb…

Spatiotemporal Nonlinear Beam Shaping

The reshaping of multimode waves in optical fibers is a process where the spatial and spectral degrees of freedom are inherently coupled. Our experiments demonstrate that pumping a graded-index multimode fiber with sub-ns pulses from a microchip Nd:YAG laser leads to supercontinuum generation with a uniform bell-shaped spatial beam profile.

Radiating and nonradiating behavior of hyperbolic-secant, raised-cosine, and Gaussian input light pulses in dispersion-managed fiber systems.

We address the problem of optical light pulses, called dressed pulses, which do not match the stationary pulse profile of a dispersion-managed (DM) fiber system and we theoretically analyze the associated radiation. Comparing hyperbolic-secant, raised-cosine, and Gaussian pulse envelopes, we show that the general radiation figure is highly sensitive to the input pulse profile. As common general features for these pulse profiles, we find a rich variety of dynamical states that includes weak-, moderate-, and strong-radiation states, depending on the map strength of the DM fiber system. We demonstrate the existence of two intervals of map strengths where the emitted radiation is of considerabl…

Testing and extrapolating the nonlinear robustness of modulation formats

The comparison of the robustness of modulation formats in fiber transmission systems facing nonlinear impairments and noise is carried out experimentally using a test link. Special techniques may be necessary when extrapolating by numerical simulations.

Quasi-soliton spatial autoguidé en milieu non lineaire quadratique

International audience; Nous démontrons ici des phénomènes d'autoguidage optique existant dans les milieux à non-linéarités quadratiques. En plus de la formation puis disparition d'un phénomène auto confiné, nous observons des effets de commutation ultrarapide et de démultiplication spatiale, ainsi qu'une restructuration temporelle suivie d'élargissements spectraux.

Nonlinear spatial self-cleaning in multimode amplifying fiber and fiber laser cavity

During the last years, multimode fibers (MMFs) were used as an experimental platform for the observation of complex nonlinear propagation phenomena, thanks to their additional spatiotemporal degrees of freedom with respect to single mode fibers. Multimode solitons [1], geometric parametric instability [2], self-induced beam cleaning (SBC) [3] and supercontinuum generation have been reported [4]. In all of these situations considered so far the MMFs were standard graded-index fibers: the intermodal interactions took place in a conservative system (propagation losses were negligible). In this work we have experimentally investigated the Kerr SBC in three dissipative systems: a MMF with signif…

Frequency tunable polarization and intermodal modulation instability in high birefringence holey fiber

International audience; We present an experimental analysis of polarization and intermodal noise-seeded parametric amplification, in which dispersion is phase matched by group velocity mismatch between either polarization or spatial modes in birefringent holey fiber with elliptical core composed of a triple defect. By injecting quasi-CW intense linearly polarized pump pulses either parallel or at 45 degrees with respect to the fiber polarization axes, we observed the simultaneous generation of polarization or intermodal modulation instability sidebands. Furthermore, by shifting the pump wavelength from 532 to 625 nm, we observed a shift of polarization sidebands from 3 to 8 THz, whereas int…

Optical OCDMA enhanced by nonlinear optics

International audience; Intended for the next generation of optical access networks, OCDMA is of great interest to meet the demand of increasing the number of users per access fiber, especially as spectral phase coding increases its performance in the optical domain. This, however, requires handling broad spectra and short pulses, which are best dealt with using opto-electronic or all-optical devices instead of slower electronics. Among others, we demonstrate spectral-phase-coded OCDMA using a fiber-based saturable absorber as thresholding in the receiver.

Nonlinear modal control by Kerr beam self-cleaning and wavefront shaping in graded-index multimode fiber

International audience

Spatial beam cleaning in quadratic nonlinear medium

We show experimentally that a laser beam scrambled by propagation in a short segment of multimode fiber may be cleaned by the nonlinear propagation in KTP cristal with type-II second-harmonic generation.

Coherent wavelength generation in multimode fibers

National audience

High performance configuration of all-raman N × 40 Gbit/s RZ-DPSK systems over ultrawave<sup>TM</sup> maps

In order to explore the impact of the DPSK format on best system configuration, and to cross-check the simulation tools, transmission experiments involving 16 × 40 Gbit/s WDM channels on a recirculating loop including a symmetric UltrawaveTM fiber dispersion map are performed. In these experiments the RZ-DPSK format is used, and each 100 km span is brought to optical transparency with 75%(25%) of backward (forward) Raman gain. The pre-compensation is experimentally varied, and a significant transmission improvement after 4000 km for the pre-compensation of -350 ps/nm is observed.

CSRZ-ASK and DPSK 40 Gb/s All-Raman WDM Transmission Based on UltraWave Fiber

In this paper, we report a complete experimental and numerical analysis of 40 Gb/s WDM ultra long-haul (ULH) transmission using CSRZ-DPSK and CSRZ-ASK modulation formats on UltraWavetrade fiber spans. Experimental results compare well with full numerical simulations

Multidimensional Shaping of SpatiotemporalWaves in Multimode Nonlinear Fibers (invited)

International audience

Performance Comparison of SSMF and UltraWave Fibers for Ultra-Long-Haul 40-Gb/s WDM Transmission

International audience; We experimentally compare the performance of standard single-mode fiber (SSMF) and UltraWave fiber (UWF) for ultra-long-haul (ULH) 40-Gb/s wavelength-division-multiplexing transmissions. We used the carrier-suppressed return-to-zero amplitude-shift-keying (CSRZ-ASK) and the carrier-suppressed return-to-zero differential-phase-shift-keying (CSRZ-DPSK) formats, which are particularly well-adapted to 40-Gb/s pulse-overlapped propagation. We demonstrate that transmission distance well beyond 2000 km can be reached on UWF with both the CSRZ-ASK and CSRZ-DPSK formats, or on SSMF with the CSRZ-DPSK format only, thus indicating that SSMF-based infrastructure of incumbent car…

Observation of Frequency Tunable Cross-Phase Modulation Instabilities in Highly Birefringent Photonic Crystal Fiber

We observed frequency tunable modulation instability owing to cross-phase modulation in normal group velocity dispersion regime of a birefringent holey fiber. Sideband shifts were 3-8 THz for polarization and 30-60 THz for modal instabilities.

Nonlinear Sculpturing of Optical Pulses in Fibre Systems

The interplay among the effects of dispersion, nonlinearity and gain/loss in optical fibre systems can be efficiently used to shape the pulses and manipulate and control the light dynamics and, hence, lead to different pulse-shaping regimes [1,2]. However, achieving a precise waveform with various prescribed characteristics is a complex issue that requires careful choice of the initial pulse conditions and system parameters. The general problem of optimisation towards a target operational regime in a complex multi-parameter space can be intelligently addressed by implementing machine-learning strategies. In this paper, we discuss a novel approach to the characterisation and optimisation of …

Spatio-temporal beam dynamics in multimode nonlinear optical fibers

We overview recent advances in the spatio-temporal nonlinear dynamics of optical pulses propagating in multimode optical fibers. The Kerr effect leads to spatial beam self-cleaning in a graded-index multimode optical fiber, followed by sideband series generation spanning multiple octaves. Effectively single mode supercontinuum spanning from the visible to the mid-infrared was also demonstrated. Enhancement of Kerr beam self-cleaning was observed in active fiber with quasi-step index profile. Moreover, mutual self-cleaning was recently reported for both the fundamental and the second harmonic beams in optically poled multimode fibers with cubic and quadratic nonlinearity.

Highly efficient few-mode spatial beam self-cleaning at 15µm

We experimentally demonstrate that spatial beam self-cleaning can be highly efficient when obtained with a few-mode excitation in graded-index multimode optical fibers. By using 160 ps long, highly chirped (6 nm bandwidth at -3dB) optical pulses at 1562 nm, we demonstrate a one-decade reduction of the power threshold for spatial beam self-cleaning, with respect to previous experiments using pulses with laser wavelengths at 1030-1064 nm. Self-cleaned beams remain spatio-temporally stable for more than a decade of their peak power variation. The impact of input pulse temporal duration is also studied.

Nonlinear Multimode Fiber Optics

We overview recent advances in the nonlinear optics of multimode optical fibers, including ultrabroadband sideband and supercontinuum generation, Kerr and Raman beam cleanup, modal modulation instabilities, four wave mixing, and second harmonic beam cleaning.

Cascaded intermodal four-wave mixing in a few-mode fiber

During the last few years, intensive works on multimode fibers allowed for the observation of a series of complex and novel nonlinear spatiotemporal phenomena such as: multimode solitons, geometric parametric instability, supercontinuum generation, and self-induced beam cleaning [1-4]. Among these phenomena, intermodal four-wave mixing (IMFWM) demonstrated larger frequency shifts in comparison with single-mode fibers. In this work, we studied IMFWM in a few-mode graded-index fiber (GRIN-FMF) pumped in the normal dispersion regime at 1064 nm. We report parametric sidebands detuned by hundreds of THz from the pump.

Optical Fibers Enter a New Space-Time Era

We show experimentally a new type of parametric instability associated with the original phenomenon of beam self-cleaning in multimode fibers. Our experimental results are in good agreement with numerical solutions of the Gross-Pitaevskii equation.

Spatial Beam Evolution in Nonlinear Multimode Fibers

We discuss some recent results illustrating the role of input wave-front shaping, propagation dynamics and output beam diagnostics in order to observe spatial beam cleaning in nonlinear multimode fibers and amplifiers.

Supercontinuum généré par fibre optique à cristal photonique pour l'accès multiple à répartition par code

National audience

Second harmonic generation and beam cleaning in optically poled multimode graded-index fibers

Recent experimental results have confirmed that nonlinear effects in multimode graded-index (MM-GRIN) fibers lead to a wealth of observable spatiotemporal effects. In spite of the large number of modes supported by the fiber, by increasing the input power the transverse profile evolves in a clean bell-shaped beam [1, 2]. Next, the input laser line experiences a strong spectral broadening and Geometric Parametric Instability (GPl) peaks are observed [3].

Nonlinear dynamics in multimode optical fibers (invited)

International audience

Spatio-Temporal Beam Mapping for Studying Nonlinear Dynamics in Graded Index Multimode Fiber

We experimentally demonstrate high-resolution mapping of the spatio-temporal dynamics of the beam cleaning process in graded index multimode fibers. This high-resolution characterization reveals the time-dependent nature of the beam self-cleaning process.

Spatiotemporal pulse shaping with multimode nonlinear guided waves

We experimentally and theoretically investigate complex temporal pulse reshaping that accompanies Kerr beam self-cleaning in multimode optical fibers. We also study the output beam shape dependence on initial conditions.

Perturbations, internal modes and noise in dispersion-managed soliton transmission

We apply the theory of soliton internal modes to characterize the dynamics of small perturbations in the dispersion-managed soliton transmission regime. We extend our study to the case of random initial perturbations calculating several realizations and obtaining accurate descriptions of their statistics.

Can SSMF handle ULH 40-Gb/s WDM transmission?

Second harmonic generation in multimode graded-index fibers: spatial beam cleaning and multiple harmonic sideband generation

We study experimentally and numerically the spectral and spatial dynamics of second harmonic generation in an all-optically poled multimode graded-index fiber. In contrast with poled single-mode fibers, in a multimode graded-index fiber a pump can generate a series of sharp sidebands around its second harmonic (SH) that originate from the sub-millimetric periodic evolution of the intensity at the fundamental frequency. The mutual interaction between the fundamental and its SH may also strongly affect the spatial distribution of guided light for both colors: when increasing the pump power, both fundamental and SH output beams evolve from disordered multimode speckles into two bell-shaped bea…

Managing Group and Phase Birefringence for Nonlinear Optics in Photonic Crystal Fibers

A novel design of birefringent photonic crystal fibers with stress applying parts permits to manage the wavelength dependence of group and phase birefringence. Applications to vector frequency conversion and soliton polarization instabilities are discussed.

Multilevel system optimisation via nonlinearity management

Nonlinearity management is explored as a multilevel tool to obtain maximum transmission reach in a WDM system. A technique for the fast calculation of the optimal dispersion pre-compensation in systems with distributed amplification is proposed.

Control of signal coherence in parametric frequency mixing with incoherent pumps: Narrowband mid-infrared light generation by downconversion of broadband amplified spontaneous emission source at 1550 nm

International audience; We study, with numerical simulations using the generalized nonlinear envelope equation, the processes of optical parametric and difference- and sum-frequency generation (SFG) with incoherent pumps in optical media with both quadratic and third-order nonlinearity, such as periodically poled lithium niobate. With ultrabroadband amplified spontaneous emission pumps or continua (spectral widths > 10 THz), group-velocity matching of a near-IR pump and a short-wavelength mid-IR (MIR) idler in optical parametric generation may lead to more than 15-fold relative spectral narrowing of the generated MIR signal. Moreover, the SFG process may also lead to 6-fold signal coherence…

Performance des emetteurs duobinaires pour la transmisión longue distance à 40Gb/s

National audience

Nonlinear dynamics of spatio-temporal waves in multimode fibres

International audience

Kerr beam self-cleaning in the telecom band

Multimode graded index (GRIN) fibers received a renewed interest in recent years, in particular for the development of new laser sources [1]. In many cases, the use of GRIN fibers is limited by multimodal propagation, leading to a spatially modulated intensity distribution (speckles) at the fiber output. Recent studies have found that quasi-single mode propagation can be recovered in GRIN fibers by the so-called Kerr self-cleaning effect [2]. It consists in the spontaneous recovery of the spatial beam quality, without any frequency shift [2] (as opposed to, e.g., Raman beam self-cleaning [3]). This nonlinear process was only observed so far at laser wavelengths around 1 μm, for peak power l…

Collision-induced polarization scattering of dispersion managed solitons

Using a multiscale expansion of coupled nonlinear Schrodinger equations we study the role of map strength and channel spacing for two colliding solitons. We numerically study then the depolarization caused by collisions of dispersion-managed vector solitons.

Experimental evidence of the real multimode nature of geometric parametric instability

We show experimentally that geometric parametric instability in graded-index multimode fibers is composed by several multimode spectral components. The experimental observation is obtained by using a new 3D technique of high-resolution spatial and spectral analysis.

Analyse statistique de la phase des solitons optiques

On analyse numeriquement la statistique de la phase des solitons optiques et on arrive a determiner la fonction de densite de probabilite. Nos resultats sont en accord avec les theories existantes, qui sont basees sur les proprietes des solitons.

Kerr Beam Self-Cleaning in Multimode Fibers

We overview recent experimental results of beam self-cleaning observed in various types of multimode fibers. We analyze the output spatial beam shapes and their connection with the refractive index profile of the fibers.

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

International audience; 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.

Adaptive Kerr-Assisted Transverse Mode Selection in Multimode Fibers

Multimode optical fibers (MMFs) have recently regained interest because of the degrees of freedom associated with their different eigenmodes. In the nonlinear propagation regime in particular, new phenomena have been unveiled in graded-index (GRIN) MMFs such as geometric parametric instabilities and Kerr beam self-cleaning [1, 2]. The speckled pattern observed at the output of the MMF at low powers, is transformed at high powers into a bell-shaped beam close to the fundamental mode. Recent work has also demonstrated that Kerr beam self-cleaning can lead to a low-order spatial mode, different from a bell-shape, by adjusting the laser beam in-coupling conditions [3]. An attractive way to syst…

Spatiotemporal beam shaping in nonlinear multimode fibers

Kerr beam self-cleaning in graded-index multimode fibers is accompanied by power-dependent temporal pulse reshaping. We explore the complex nonlinear dynamics with a single long pulse, where the optical power is continuously varied across its profile.

Performance Comparison of Duobinary Modulation Formats for 40 Gb/s Long-Haul WDM Transmissions

With their compact spectrum and high tolerance to residual chromatic dispersion, duobinary formats are attractive for the deployment of 40 Gb/s technology on 10 Gb/s WDM Long-Haul transmission infrastructures. Here, we compare the robustness of various duobinary formats when facing 40 Gb/s transmission impairments.

Nonlinear Dynamics in multimode fibers

International audience

Optical CDMA enhanced by nonlinear optics

Intended for the next generation of optical access networks, OCDMA is of great interest to meet the demand of increasing the number of users per access fiber, especially as spectral phase coding increases its performance in the optical domain. This, however, requires handling broad spectra and short pulses, which are best dealt with using opto-electronic or all-optical devices instead of slower electronics. Among others, we demonstrate spectral-phase-coded OCDMA using a fiber-based saturable absorber as thresholding in the receiver.

Multi-level optimization of a fiber transmission system via nonlinearity management

Nonlinearity management is explored as a complete tool to obtain maximum transmission reach in a WDM fiber transmission system, making it possible to optimize multiple system parameters, including optimal dispersion pre-compensation, with fast simulations based on the continuous-wave approximation. © 2006 Optical Society of America.