Stabilized single-frequency sub-kHz linewidth Brillouin fiber laser cavity operating at 1 µm.

We experimentally demonstrate a stabilized single-frequency Brillouin fiber laser operating at 1.06 µm by means of a passive highly nonlinear fiber (HNLF) ring cavity combined with a phase-locking loop scheme. The stimulated Brillouin scattering efficiency is first investigated in distinct single-mode germanosilicate core fibers with increasing G e O 2 content. The most suitable fiber, namely, 21 mol.% G e O 2 core fiber, is used as the Brillouin gain medium in the laser cavity made with a 15-m-long segment. A Stokes lasing threshold of 140 mW is reported. We also show significant linewidth narrowing (below 1 kHz) as well as frequency noise reduction compared to that of the initial pump in our mode-hop free Brillouin fiber laser.

Design and fabrication of dispersion controlled highly nonlinear fibers for far-detuned 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 ß2 and ß4) at 1.55 µm 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.

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 nonequilibrium 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 any adjustable parameter. Experiments realized in multimode optical fibers with an applied external stress evidence the process of thermalization in the presence of strong disorder.

Electro-optic dual-comb spectrometer in the thulium amplification band for gas sensing applications.

We demonstrate a dual-comb spectrometer based on the direct electro-optic modulation of a continuous-wave laser operating in the thulium amplification band. We show that the emergent two-micrometer technology is already suitable for developing all-fibered dual-comb setups employed here for gas sensing applications. By performing spectroscopic measurements around two micrometers on carbon dioxide, we obtain very good agreement between the experimental results and calculations provided by the HITRAN database. These results pave the way to the extension of electro-optic dual-comb spectrometry in the mid-infrared region.

Intense stimulated Raman scattering in CO2-filled hollow-core fibers.

We demonstrate experimentally, the generation of an intense broadband comb-like spectrum spontaneously built up through stimulated Raman scattering in a low-pressure CO2-filled hollow-core photonic crystal fiber pumped by a single infrared pump.

Nonlinear polarization dynamics of Kerr beam self-cleaning in a graded-index multimode optical fiber.

We experimentally study polarization dynamics of Kerr beam self-cleaning in a graded-index multimode optical fiber. We show that spatial beam cleaning is accompanied by nonlinear polarization rotation and a significant increase of the degree of linear polarization.

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.

Si-rich Si nitride waveguides for optical transmissions and toward wavelength conversion around 2 µm.

We show that subwavelength Si-rich nitride waveguides efficiently sustain high-speed transmissions at 2 µm. We report the transmission of a 10 Gbit/s signal over 3.5 cm with negligible power penalty. Parametric conversion in the pulsed pump regime is also demonstrated using the same waveguide structure with an efficiency as high as -18 dB.

Publisher's Note: Observation of Geometric Parametric Instability Induced by the Periodic Spatial Self-Imaging of Multimode Waves [Phys. Rev. Lett. 116, 183901 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.116.183901.

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

Spatiotemporal 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-ns pulses at 1064 nm. The experimentally observed frequency spacing among sidebands agrees well with analytical predictions and numerical simulations. The first-order peaks are located at the considerably large detuning of 123.5 THz from the pump. These results open the remarkable possibility to convert a near-infrared laser directly into a broad spectral range spanning visible and infrared wavelengths, by means of a single resonant parametric nonlinear effect occurring in the normal dispersion regime. As further evidence of our strong space-time coupling regime, we observed the striking effect that all of the different sideband peaks were carried by a well-defined and stable bell-shaped spatial profile.

Translation of pre-spliced RNAs in the nuclear compartment generates peptides for the MHC class I pathway.

The scanning of maturing mRNAs by ribosomes plays a key role in the mRNA quality control process. When ribosomes first engage with the newly synthesized mRNA, and if peptides are produced, is unclear, however. Here we show that ribosomal scanning of prespliced mRNAs occurs in the nuclear compartment, and that this event produces peptide substrates for the MHC class I pathway. Inserting antigenic peptide sequences in introns that are spliced out before the mRNAs exit the nuclear compartment results in an equal amount of antigenic peptide products as when the peptides are encoded from the main open reading frame (ORF). Taken together with the detection of intron-encoded nascent peptides and RPS6/RPL7-carrying complexes in the perinucleolar compartment, these results show that peptides are produced by a translation event occurring before mRNA splicing. This suggests that ribosomes occupy and scan mRNAs early in the mRNA maturation process, and suggests a physiological role for nuclear mRNA translation, and also helps explain how the immune system tolerates peptides derived from tissue-specific mRNA splice variants.

High-gain far-detuned nonlinear frequency conversion in a few-mode graded-index optical fiber.

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  µ m , and more specifically achieving gains of hundreds of dB per meter below 0.65  µ m and beyond 3.5  µ m . Interestingly, our findings highlight the potential of graded-index fibers for enabling high-gain wavelength conversion into the strong-loss spectral region of silica. Such advancements require an accurate interpretation of intramodal and intermodal four-wave mixing processes.

Cross-phase modulational instability induced by Raman scattering in highly birefringent fiber.

We report experimental and theoretical studies of Raman-induced cross-phase modulational instabilities (XPMI) in a high-birefringence, normally dispersive optical fiber. Experimental results reveal that the Raman-Stokes wave, generated by a quasi-CW pump beam, interacts with the latter to create a novel type of XPMI sidebands. These sidebands are characterized by a narrow gain bandwidth. The sideband frequencies are well reproduced by a linear stability analysis as well as by full numerical solutions of the coupled generalized nonlinear Schrödinger equations.

Experimental generation of optical flaticon pulses.

We experimentally investigate the nonlinear reshaping of a continuous wave that leads to chirp-free and flat-top intense pulses or flaticons exhibiting strong temporal oscillations at their edges and a stable self-similar expansion upon propagation of their central region. This study was performed in the normal dispersion regime of a nonzero dispersion-shifted fiber and involved a sinusoidal phase modulation of the continuous wave. Our fiber optics experiment is analogous to considering the collision between oppositely directed currents near the beach, and it may open the way to new investigations in the field of hydrodynamics.

Random walks and random numbers from supercontinuum generation.

We report a numerical study showing how the random intensity and phase fluctuations across the bandwidth of a broadband optical super-continuum can be interpreted in terms of the random processes of random walks and Lévy flights. We also describe how the intensity fluctuations can be applied to physical random number generation. We conclude that the optical supercontinuum provides a highly versatile means of studying and generating a wide class of random processes at optical wavelengths.

EMMPRIN promotes angiogenesis through hypoxia-inducible factor-2alpha-mediated regulation of soluble VEGF isoforms and their receptor VEGFR-2.

Extracellular matrix metalloproteinase inducer (EMMPRIN/CD147) is thought to promote tumor angiogenesis mostly through its protease-inducing function and more recently by its ability to increase tumor cell expression of vascular endothelial growth factor (VEGF). In this study, we present evidence that EMMPRIN can promote angiogenesis by a direct effect on endothelial cells through a paracrine regulation of the VEGF/VEGF-receptor (VEGFR) system. Using human microvascular endothelial cell line-1 endothelial cells, we show that EMMPRIN selectively increased the soluble VEGF isoforms (121 and 165), but not the matrix-bound VEGF 189 form. In addition, EMMPRIN up-regulated the expression of VEGFR-2 without an effect on VEGFR-1. This increase in VEGFR-2 was responsible for the observed EMMPRIN stimulation of the migratory and tube formation capacity of endothelial cells. EMMPRIN's effects, which were matrix metalloproteinase and urokinase-type plasminogen activator independent, were mediated primarily through hypoxia-inducible factor-2alpha expression, also up-regulated by EMMPRIN. VEGFR-2 increase was also observed in vivo in a mouse model of xenograph tumors overexpressing EMMPRIN. These results suggest that in addition to increasing protease production, EMMPRIN may contribute to the formation of a reactive stroma also through the up-regulation of hypoxia-inducible factor-2alpha, VEGFR-2, and the soluble forms of VEGF in endothelial cells, thus directly regulating the angiogenic process.

Peregrine soliton generation and breakup in standard telecommunications fiber.

We present experimental and numerical results showing the generation and breakup of the Peregrine soliton in standard telecommunications fiber. The impact of nonideal initial conditions is studied through direct cutback measurements of the longitudinal evolution of the emerging soliton dynamics and is shown to be associated with the splitting of the Peregrine soliton into two subpulses, with each subpulse itself exhibiting Peregrine soliton characteristics. Experimental results are in good agreement with simulations.

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

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibers (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 fibers. Here we show that the associated self-induced spatiotemporal reshaping allows for improving the performances of nonlinear fluorescence (NF) microscopy and endoscopy using multimode optical fibers. 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 (SC) generation is well-suited for large-band NF imaging in visible and infrared domains. We substantiated our findings by multiphoton fluorescence imaging in both microscopy and endoscopy configurations.

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. 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, and open new opportunities for coherent beam combining.

Experimental evidence of Brillouin-induced polarization wheeling in highly birefringent optical fibers.

We study the influence of Stimulated Brillouin Scattering on the polarization stabilization of a light beam propagating in a highly-birefringent optical fiber. In particular, due to a saturation effect, we find that the output polarization lies on a ring when the polarization is represented onto the Poincaré sphere.