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Guy Millot

Publications and source records attributed to Guy Millot.

At least 19 recordsLinked to original sources
arXiv2024

High-gain far-detuned nonlinear frequency conversion in optical fibers: intramodal vs. intermodal processes

We present theoretical and experimental evidence of high-gain far-detuned nonlinear frequency conversion, extending towards both the visible and the mid-infrared, in a few-mode graded-index silica fiber pumped at 1.064 $\mu$m, and more specifically achieving gains of hundreds of dB per meter below 0.65 $\mu$m and beyond 3.5 $\mu$m. Our findings highlight the potential of graded-index fibers in terms of strong modal confinement over an ultrabroad spectral range for enabling high-gain wavelength conversion. Such advancements require an accurate interpretation of intramodal and intermodal four-wave mixing processes.

physics.optics↗
arXiv2024

Optimum design of NOLM-driven mode-locked fiber lasers

Most of the saturable absorbers commonly used to perform mode locking in laser cavities affect the trigger conditions of laser oscillation, which requires manually forcing the laser start-up by various means such as polarization controllers. We present a procedure for designing a laser cavity driven by a nonlinear optical loop mirror, which allows the laser to operate optimally without interfering with the oscillation triggering conditions, thus opening up possibilities for integration of this type of laser.

physics.optics↗
arXiv2024

Strategies for accessing the multi-pulse regime of mode-locked fiber lasers

Important ongoing research on mode-locked fiber lasers aims at developing new types of multi-soliton regimes, such as soliton molecules, molecular complexes or soliton crystals. The on-demand generation of such multi-pulse structures is a major challenge, whereas experiments generally involve a tedious trial-and-error adjustment of the laser parameters. Here, we present an approach based on a gradual and calibrated adjustment of the system configuration, which employs efficient parameter routes to reach well-defined multi-pulse regimes. Our numerical simulations show that once the mode-locking threshold is reached, we can adjust the laser parameters gradually to force the evolution of the laser dynamics towards multi-pulse structures with fewer distortion in their intensity profiles, which are accessible at reduced pump power levels.

physics.optics↗
arXiv2024

Design and fabrication of dispersion controlled highly nonlinear fibers for far-tuned four-wave mixing frequency conversion

We report on the conception, fabrication and characterization of a new concept of optical fiber enabling a precise control of the ratio between the 2nd and 4th-order of chromatic dispersion (respectively \b{eta}2 and \b{eta}4) at 1.55 micro-meter which is at the heart of the Four-Wave-Mixing (FWM) generation. For conventional highly nonlinear fiber the sensitivity of this ratio to fiber geometry fluctuations is very critical, making the fabrication process challenging. The new design fiber reconciles the accurate control of chromatic dispersion properties and fabrication by standard stack and draw method, allowing a robust and reliable method against detrimental fluctuations parameters during the fabrication process. Experimental frequency conversion with FWM in the new design fiber is demonstrated.

physics.optics↗
arXiv2023

Rayleigh-Jeans thermalization vs beam cleaning in multimode optical fibers

Classical nonlinear waves exhibit, as a general rule, an irreversible process of thermalization toward the Rayleigh-Jeans equilibrium distribution. On the other hand, several recent experiments revealed a remarkable effect of spatial organization of an optical beam that propagates through a graded-index multimode optical fiber (MMF), a phenomenon termed beam self-cleaning. Our aim here is to evidence the qualitative impact of disorder (weak random mode coupling) on the process of Rayleigh-Jeans thermalization by considering two different experimental configurations. In a first experiment, we launch speckle beams in a relatively long MMF. Our results report a clear and definite experimental demonstration of Rayleigh-Jeans thermalization through light propagation in MMFs, over a broad range of kinetic energy (i.e., degree of spatial coherence) of the injected speckle beam. In particular, the property of energy equipartition among the modes is clearly observed in the condensed regime. The experimental results also evidence the double turbulence cascade process: while the power flows toward the fundamental mode (inverse cascade), the energy flows toward the higher-order modes (direct cascade). In a 2nd experiment, a coherent laser beam is launched into a relatively short MMF length. It reveals an effect of beam cleaning driven by an incipient process of Rayleigh-Jeans thermalization. As discussed through numerical simulations, the fast process of Rayleigh-Jeans thermalization observed in the 1st experiment can be attributed due to a random phase dynamics among the modes, which is favoured by the injection of a speckle beam and the increased impact of disorder in the long fiber system.

physics.optics↗
arXiv2023

Near-infrared dual-comb spectroscopy of CO2 and N2O with a discretized highly nonlinear fiber

In this paper, we introduce an all-fibered dual-comb spectrometer based on a new design of highly nonlinear fiber to efficiently convert frequency combs from 1.55 micron to 2 micron We show that our spectrometer can be used to measure absorption profiles of rovibrational transitions of CO2 and N2O molecules, and especially their collisional self-broadening coefficients. The results show very good agreement with the HITRAN database and thus further measurements have been performed on a mixture CO2 /N2O to measure the broadening of the CO2 absorption lines resulting from the presence of N2O.

physics.optics↗
arXiv2023

Experimental measurements of the transfer function of a nonlinear optical loop mirror

Measurement of the average values of the input and output powers of a device can give insight into the transfer function (TF) of that device, but this approach usually hides the real impact of certain propagation phenomena. However, to the best of our knowledge, measurements of the TF of nonlinear optical loop mirrors have always been carried out using this approach [1-3], which may lead to underestimating the impact of dispersive and nonlinear effects. Here we present the experimental measurement of the TF of a nonlinear optical loop mirror (NOLM), made from the experimental measurements of the input and output intensity profiles of the device, using a frequency-resolved optical gating (FROG) technique [4-6]. Our approach clearly highlights the impact of dispersion effects and Kerr nonlinearity on the NOLM's TF.

physics.optics↗
arXiv2023

Plug-and-play measurement of chromatic dispersion by means of two-photon interferometry

Since the first proof-of-principle experiments 25 years ago, quantum metrology has matured from fundamental concepts to versatile and powerful tools in a large variety of research branches, such as gravitational-wave detection, atomic clocks, plasmonic sensing, and magnetometry. At the same time, two-photon interferometry, which underpins the possibility of entanglement to probe optical materials with unprecedented levels of precision and accuracy, holds the promise to stand at the heart of innovative functional quantum sensing systems. We report a novel quantum-based method for measuring the frequency dependence of the velocity in a transparent medium, i.e, the chromatic dispersion (CD). This technique, using energy-time entangled photons, allows straightforward access to CD value from the visibility of two-photon fringes recorded in a free evolution regime. In addition, our quantum approach features all advantages of classical measurement techniques, i.e, flexibility and accuracy, all in a plug-and-play system.

quant-ph↗
arXiv2022

Interplay of thermalization and strong disorder: Wave turbulence theory, numerical simulations, and experiments in multimode optical fibers

We address the problem of thermalization in the presence of a time-dependent disorder in the framework of the nonlinear Schrödinger (or Gross-Pitaevskii) equation with a random potential. The thermalization to the Rayleigh-Jeans distribution is driven by the nonlinearity. On the other hand, the structural disorder is responsible for a relaxation toward the homogeneous equilibrium distribution (particle equipartition), which thus inhibits thermalization (energy equipartition). On the basis of the wave turbulence theory, we derive a kinetic equation that accounts for the presence of strong disorder. The theory unveils the interplay of disorder and nonlinearity. It unexpectedly reveals that a non-equilibrium process of condensation and thermalization can take place in the regime where disorder effects dominate over nonlinear effects. We validate the theory by numerical simulations of the nonlinear Schrödinger equation and the derived kinetic equation, which are found in quantitative agreement without using adjustable parameters. Experiments realized in multimode optical fibers with an applied external stress evidence the process of thermalization in the presence of strong disorder.

physics.optics↗
arXiv2022

Isotope Ratio Dual-Comb Spectrometer

We demonstrate the use of dual-comb spectroscopy for isotope ratio measurements. We show that the analysis spectral range of a free-running near-infrared dual-comb spectrometer can be extended to the mid-infrared by difference frequency generation to target specific spectral regions suitable for such measurements, and especially the relative isotopic ratio $δ{}^{13}$C. The measurements performed present a very good repeatability over several days with a standard deviation below 2$\unicode{x2030}$ for a recording time of a few tens of seconds, and the results are compatible with measurements obtained using an isotope ratio mass spectrometer. Our setup also shows the possibility to target several chemical species without any major modification, which can be used to measure other isotopic ratios. Further improvements could decrease the uncertainties of the measurements, and the spectrometer could thus compete with isotope ratio spectrometers currently available on the market.

physics.ins-det↗
arXiv2021

Weak Langmuir turbulence in disordered multimode optical fibers

We consider the propagation of temporally incoherent waves in multimode optical fibers (MMFs) in the framework of the multimode nonlinear Schrödinger (NLS) equation accounting for the impact of the natural structural disorder that affects light propagation in standard MMFs (random mode coupling and polarization fluctuations). By averaging the dynamics over the fast disordered fluctuations, we derive a Manakov equation from the multimode NLS equation, which reveals that the Raman effect introduces a previously unrecognized nonlinear coupling among the modes. Applying the wave turbulence theory on the Manakov equation, we derive a very simple scalar kinetic equation describing the evolution of the multimode incoherent waves. The structure of the kinetic equation is analogous to that developed in plasma physics to describe weak Langmuir turbulence. The extreme simplicity of the derived kinetic equation provides physical insight into the multimode incoherent wave dynamics. It reveals the existence of different collective behaviors where all modes self-consistently form a multimode spectral incoherent soliton state. Such an incoherent soliton can exhibit a discrete behavior characterized by collective synchronized spectral oscillations in frequency space. The theory is validated by accurate numerical simulations: The simulations of the generalized multimode NLS equation are found in quantitative agreement with those of the derived scalar kinetic equation without using adjustable parameters.

physics.optics↗
arXiv2020

Dramatic acceleration of wave condensation mediated by disorder in multimode fibers

Classical nonlinear waves exhibit a phenomenon of condensation that results from the natural irreversible process of thermalization, in analogy with the quantum Bose-Einstein condensation. Wave condensation originates in the divergence of the thermodynamic equilibrium Rayleigh-Jeans distribution, which is responsible for the macroscopic population of the fundamental mode of the system. However, achieving complete thermalization and condensation of incoherent waves through nonlinear optical propagation is known to require prohibitive large interaction lengths. Here, we derive a discrete kinetic equation describing the nonequilibrium evolution of the random wave in the presence of a structural disorder of the medium. Our theory reveals that a weak disorder accelerates the rate of thermalization and condensation by several order of magnitudes. Such a counterintuitive dramatic acceleration of condensation can provide a natural explanation for the recently discovered phenomenon of optical beam self-cleaning. Our experiments in multimode optical fibers report the observation of the transition from an incoherent thermal distribution to wave condensation, with a condensate fraction of up to 60% in the fundamental mode of the waveguide trapping potential.

physics.optics↗
arXiv2020

Spatiotemporal beam self-cleaning for high-resolution nonlinear fluorescence imaging with multimode fibres

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibres (MMFs) has been recently reported by different research groups. Driven by the interplay between Kerr effect and beam self-imaging, BSC counteracts random mode coupling, and forces laser beams to recover a quasi-single mode profile at the output of GRIN fibres. Here we show that the associated self-induced spatiotemporal reshaping allows for improving the performances of nonlinear fluorescence microscopy and endoscopy using multimode optical fibres. We experimentally demonstrate that the beam brightness increase, induced by self-cleaning, enables two and three-photon imaging of biological samples with high spatial resolution. Temporal pulse shortening accompanying spatial beam clean-up enhances the output peak power, hence the efficiency of nonlinear imaging. We also show that spatiotemporal supercontinuum generation is well-suited for large-band nonlinear fluorescence imaging in visible and infrared domains. We substantiated our findings by multiphoton fluorescence imaging in both microscopy and endoscopy configurations.

physics.optics↗
arXiv2020

Coherent combining of self-cleaned multimode beams

A low intensity light beam emerges from a graded-index, highly multimode optical fibre with a speckled shape, while at higher intensity the Kerr nonlinearity may induce a spontaneous spatial self-cleaning of the beam [1,2]. Here, we reveal that we can generate two self-cleaned beams with a mutual coherence large enough to produce a clear stable fringe pattern at the output of a nonlinear interferometer. The two beams are pumped by the same input laser, yet are self-cleaned into independent multimode fibres. We thus prove that the self-cleaning mechanism preserves the beams' mutual coherence via a noise-free parametric process. While directly related to the initial pump coherence, the emergence of nonlinear spatial coherence is achieved without additional noise, even for self-cleaning obtained on different modes, and in spite of the fibre structural disorder originating from intrinsic imperfections or external perturbations. Our discovery may impact theoretical approaches on wave condensation [3-5], and open new opportunities for coherent beam combining [6-9].

physics.optics↗
arXiv2019

Spatial beam self-cleaning in multimode lanthanum aluminum silicate glass fiber

We demonstrated that spatial Kerr beam self-cleaning can be obtained in a highly multimode multicomponent optical fiber based on lanthanum aluminum silicate oxide glasses (SiO2-Al2O3-La2O3), which was made by using the modified powder in tube technology (MIPT). We show how such fabrication method can provide interesting potentialities to design doped multimode optical fibers with homogeneous and quasi-parabolic refractive-index core profile for nonlinear optics applications.

physics.optics↗
arXiv2019

Turbulence-induced rogue waves in Kerr resonators

Spontaneous emergence of self-organized patterns and their bifurcations towards a regime of complex dynamics in non-equilibrium dissipative systems is a paradigm of phase transition. Indeed, the behavior of these patterns in the highly nonlinear regime remains less explored, even in recent high-quality-factor resonators such as Kerr-nonlinear optical ones. Here, we investigate theoretically and experimentally the alteration of the resulting Kerr frequency combs from the weakly to the highly nonlinear regime, in the frameworks of spatiotemporal chaos, and dissipative phase transitions. We reveal the existence of a striking and easily accessible scenario of spatiotemporal chaos, free of cavity solitons, in a monostable operating regime, wherein a transition to amplitude turbulence via spatiotemporal intermittency is evidenced. Moreover, statistics of the light bursts in the resulting turbulent regime unveils the existence of rogue waves as extreme events characterized by long-tail statistics.

physics.optics↗
arXiv2018

Refractive index profile tailoring of multimode optical fibers for the spatial and spectral shaping of parametric sidebands

We introduce the concept of spatial and spectral control of nonlinear parametric sidebands in multimode optical fibers by tailoring their linear refractive index profile. In all cases, the pump experiences Kerr self-cleaning, leading to a bell-shaped profile close to the fundamental mode. Geometric parametric instability, owing to quasi-phase-matching from the grating generated via the Kerr effect by pump self-imaging, leads to frequency multicasting of beam self-cleaning across a wideband array of sidebands. Our experiments show that introducing a gaussian dip in the refractive index profile of a graded index fiber permits to dramatically change the spatial content of spectral sidebands into higher-order modes. This is due to the breaking of oscillation synchronism among fundamental and higher-order modes. Hence modal-four-wave mixing prevails over geometric parametric instability as the main sideband generation mechanism. Observations agree well with theoretical predictions based on a perturbative analysis, and with full numerical solutions of the (3D + 1) nonlinear Schrodinger equation.

physics.optics↗