Beam self-cleaning in multimode optical fibers and hydrodynamic 2D turbulence

We experimentally demonstrate the conservation of the average mode number in the process of Kerr beam self-cleaning in a graded-index multimode optical fiber, in analogy with wave condensation in hydrodynamic 2D turbulence

Dynamics of high-energy multimode Raman solitons

The dynamics of high-energy Raman solitons in graded-index multimode fibers is both numerically and experimentally investigated. The propagation of high-power pulses produces nonlinear losses, that quench up to 80% of the fiber transmission. In such a regime, several solitons arising from the fission of ultra-short femtosecond pulses manifest unique features: pulse width, Raman self-frequency shift and soliton order remain nearly constant over a broad range of energies

Mode decomposition of Kerr self-cleaned beams by phase only SLM

Graded-index multimode optical bers have recently attracted a renewed attention, thanks to the discovery of new nonlinear eects, such as Kerr beam self-cleaning. In essence, Kerr self-cleaning involves a ow of the propagating beam energy into the fundamental mode of the ber, accompanied by a redistribution of the remaining energy among high-order modes. Increasing the fundamental mode energy leads to a signicant improvement of the output beam quality. A standard method to determine beam quality is to measure the M2 parameter. However, since self-cleaning involves the nonlinear redistribution of energy among a large number of ber modes, measuring a single beam quality parameter is not sucient to characterize the eect. A properly informative approach requires performing the mode decomposition of the output beam. Mode decomposition permits to evaluate the energy distribution among all of the excited ber modes, which enables investigations of nonlinear mode coupling processes at a qualitatively new level. In this work, we demonstrate an eciency mode decomposition method based on holography, which is suitable for analyzing the self-cleaning eect. In a theoretical study, we describe the solution of the mode decomposition problem for the modes of the gradedindex multimode ber. In an experimental investigation, we demonstrate the decomposition of both low-power (speckled) and self-cleaned beams, involving more than 80 modes

High energy pulse dynamics in multimode GRIN fibers

High energy, ultra-short multimode soliton pulse fission is observed and numerically studied in multimode GRIN fibers, showing complex dynamics bringing to multiple fundamental solitons that do not entirely follow standard single mode soliton perturbation theory predictions

Mode decomposition of multimode optical fiber beams by phase-only spatial light modulator

Multimode optical fibers (MMF) recently attracted a renewed attention, because of their potential for spatial division multiplexing, medical imaging and high-power fiber lasers, thanks to the discovery of new nonlinear optical effects, such as Kerr beam self-cleaning, spatiotemporal mode-locking, and geometric parametric instability, to name a few. The main feature of these effects is that many transverse modes are involved in nonlinear interactions. To advance our understanding, it is necessary to analyse the modal content of beams at the output of MMFs. In this work, based on a computer digital holography method using a phase-only spatial light modulator (SLM) as a correlation filter, we experimentally demonstrate a method of mode decomposition involving a large (≃80) number of fiber modes. To obtain this, we carried out a SLM calibration, and numerically investigated the most critical parameters which affect the fidelity of the decomposition, by comparing experimental and reconstructed beam patterns in both the linear (speckled structures) and in the nonlinear (self-cleaned beams) propagation regime

Generation of highly-chirped dissipative solitons in Er-doped all-fiber oscillator

The all-fiber highly-chirped dissipative soliton (HCDS) oscillator was realised at 1.5 Μm wavelength. A normal net cavity dispersion was achieved by using a conventional dispersion compensating fiber (DCF). To separate effects of the amplitude self-modulation and dissipative soliton formation, we exploit in the laser cavity both standard single mode fiber and polarization maintaining single mode fiber. The properties of the generated pulses have been varied by changing spectral filter bandwidth and DCF lengths. After compression of the nJ-level ~6 ps HCDS in the external fiber compressor, we measured the output pulse duration of 165 fs (an estimated chirp parameter 40)

Hydrodynamic 2D Turbulence and Spatial Beam Condensation in Multimode Optical Fibers

We show that Kerr beam self-cleaning results from parametric mode mixing instabilities that generate a number of nonlinearly interacting modes with randomized phases - optical wave turbulence, followed by a direct and inverse cascade towards high mode numbers and condensation into the fundamental mode, respectively. This optical self-organization effect is an analogue to wave condensation that is well known in hydrodynamic 2D turbulence

Mode decomposition method for investigating the nonlinear dynamics of a multimode beam

We overview our recent experimental studies on the nonlinear spatial reshaping of multimode beams at the output of multimode optical fibers. We use a holographic mode decomposition technique, which permits to reveal the variation of the spatial mode composition at the fiber output, as determined by either conservative (the Kerr effect) or dissipative (Raman scattering) nonlinear processes. For the first case, we consider the effect of spatial beam self-cleaning, and we compare experimental mode decompositions with predictions based on the thermodynamic theory, including the case of beams carrying nozero orbital angular momentum. For the second case, we analyze the beam mode content at the output of a Raman laser based on a graded index multimode fiber

Nonlinear multimode fiber optics: recent advances

We start by providing an overview of the emerging field of nonlinear optics in multimode optical fibers [1]. These fibers provide a simple testbed for observing complex wave propagation dynamics, in analogy with other fields of physics ranging from two-dimensional hydrodynamic turbulence and Bose-Einstein condensation. In addition, nonlinear multimode optical fibers enable new methods for achieving the ultrafast, light-activated control of temporal, spatial and spectral degrees of freedom of intense, pulsed light beams, for a range of different technological applications

Roadmap on multimode photonics

Multimode devices and components have attracted considerable attention in the last years, and different research topics and themes have emerged very recently. The multimodality can be seen as an additional degree of freedom in designing devices, thus allowing for the development of more complex and sophisticated components. The propagation of different modes can be used to increase the fiber optic capacity, but also to introduce novel intermodal interactions, as well as allowing for complex manipulation of optical modes for a variety of applications. In this roadmap we would like to give to the readers a comprehensive overview of the most recent developments in the field, presenting contributions coming from different research topics, including optical fiber technologies, integrated optics, basic physics and telecommunications