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International audience; Biomedical image mosaicking is a trending topic. It consists in computing a single large image from multiple observations, and becomes a challenging task when said observations barely overlap or are subject to illumination changes, poor resolution, blur and either highly textured or predominantly homogeneous content. Because such challenges are common in biomedical images, classical keypoint/feature-based methods perform poorly. In this paper, we propose a new framework based on pairwise template matching coupled with a constrained, confidence-driven global optimization strategy to solve the issue of microscopic biomedical image mo-saicking. First we provide experimental results that show significant improvement on a subjective level. Then we describe a new validation strategy for objective assessment, which shows improvement as well. Address

International audience; Historically, nonlinear optical phenomena such as spectral broadening by harmonic generation have been associated with crystals owing to their strong nonlinear refractive indices, which are in the range of ∼10 −14 cm 2 ∕W. This association was also the result of the limited optical power available from early lasers and the limited interaction length that the laser-crystal interaction architecture could offer. Consequently, these limitations disqualified a large number of materials whose nonlinear coefficient is lower than n 2 ∼10 −16 cm 2 ∕W as suitable materials for nonlinear optics applications. For example, it is a common practice in most of optical laboratories to consider ambient or atmospheric air as a "nonlinear optically" inert medium due to its very low nonlinear coefficient (∼10.10 −19 cm 2 ∕W) and low density. Today, the wide spread of high-power ultra-short pulse lasers on one hand, and low transmission loss and high-power handling of Kagome hollow-core photonic crystal fiber on the other hand, provide the necessary ingredients to excite strong nonlinear optical effects in practically any gas media, regardless of how low its optical nonlinear response is. By using a single table-top 1 mJ ultra-short pulse laser and an air exposed inhibited-coupling guiding hollow-core photonic crystal fiber, we observed generation of supercontinuum and third harmonic generation when the laser pulse duration was set at 600 fs and Raman comb generation when the duration was 300 ps. The supercontinuum spectrum spans over ∼1000 THz and exhibits a typical spectral-density energy of 150 nJ/nm. The dispersion profile of inhibited-coupling hollow-core fiber imprints a distinctive sequence in the supercontinuum generation, which is triggered by the generation of a cascade of four-wave mixing lines and concluded by solitonic dynamics. The Raman comb spans over 300 THz and exhibits multiple sidebands originating from N 2 vibrational and ro-vibrational Raman transitions. With the growing use of hollow-core photonic crystal fiber in different fields, the results can be applied to mitigate air nonlinear response when it is not desired or to use ambient air as a convenient nonlinear medium.

International audience; In this paper we describe an upconversion detector in the mid infrared (around 3.5 μm). We take advantage of the PPLN ridge waveguide technology to achieve single photon detection at room temperature on a single spatial mode. With a pump power of 192 mW we obtain a detection efficiency of 0.4% for 22k dark count per second, which corresponds to a noise equivalent power of 3.0 fW · Hz−1/2 and an internal conversion efficiency of 85 %/W of pump.

International audience; We demonstrate theoretically and experimentally a high level of control of the four-wave mixing process in an inert gas–filled inhibited-coupling guiding hollow-core photonic crystal fiber. The specific multiple-branch dispersion profile in such fibers allows both correlated and separable bi-photon states to be produced. By controlling the choice of gas and its pressure and the fiber length, we experimentally generate various joint spectral intensity profiles in a stimulated regime that is transferable to the spontaneous regime. The generated profiles may cover both spectrally separable and correlated bi-photon states and feature frequency tuning over tens of THz, demonstrating a large dynamic control that will be very useful when implemented in the spontaneous regime as a photon pair source.

International audience; We report the experimental observation of Kerr beam self-cleaning in a graded-index multimode fiber, leading to output beam profiles different from a bell shape, close to the LP 01 mode. For specific light injection conditions, nonlinear coupling among the guided modes can reshape the output speckle pattern generated by a pulsed beam into the low order LP 11 mode. This effect was observed in a few meters-long multimode fiber with 750 ps pulses at 1064 nm in the normal dispersion regime. The power threshold for LP 11 mode self-cleaning was about three times larger than that required for Kerr nonlinear self-cleaning into the LP 01 mode.

The performance of conventional gas sensors based on light absorption in the mid-infrared (MIR) faces the challenges of the high cost and low efficiency of photodetection at these wavelengths. In this paper, a nonlinear gas sensor based on third-harmonic generation (THG) in cascaded chalcogenide microfibers is proposed. In the first microfiber section, the input MIR light with “fingerprint” frequency has shown the ability for a large amount of gas absorption. The second microfiber section is used for THG pumped by the residual MIR light. In this process, the sensing signal is converted to the near-infrared region, and the power variation caused by the absorption is amplified due to the nonlinear relation between pump and harmonic signals. According to our analysis, the lowest methane concentration of 7.4×10−8 can be detected at a practically drawable Ae2Se3 microfiber length of 1 cm. Compared to direct MIR gas sensing, cascaded microfiber sensing has the advantages of improved sensing performance and also shorter absorption length.

International audience; We present a detailed study on the generation of widely tunable visible light through four wave mixing in specifically designed micro-structured fibers. The fiber's properties are optimized for an efficient conversion to the visible and near infrared with a combined tunability from 620 to 910 nm of a picosecond Yb-doped tunable source for biomedical applications.

International audience; In this paper, we report on a novel method to control the coherence behavior in a sum frequency generation interferometer powered by two independent pump lines. At the output of the interferometer, the two incoherent fringe patterns must be superimposed to maximize the contrast. The first step consists in canceling the differential group delay. The second one uses the phase control on one pump to synchronize the fringe patterns. This innovative method is experimentally demonstrated with a setup involving a 1544 nm signal and two pump lines around 1064 nm leading to a converted signal around 630 nm. It can be easily extended to a greater number of pump lines.

We present a reconfigurable, dynamic beam steering holographic metasurface aperture to synthesize a microwave camera at K-band frequencies. The aperture consists of a 1D printed microstrip transmission line with the front surface patterned into an array of slot-shaped subwavelength metamaterial elements (or meta-elements) dynamically tuned between "ON" and "OFF" states using PIN diodes. The proposed aperture synthesizes a desired radiation pattern by converting the waveguide-mode to a free space radiation by means of a binary modulation scheme. This is achieved in a holographic manner; by interacting the waveguide-mode (reference-wave) with the metasurface layer (hologram layer). It is shown by means of full-wave simulations that using the developed metasurface aperture, the radiated wavefronts can be engineered in an all-electronic manner without the need for complex phase-shifting circuits or mechanical scanning apparatus. Using the dynamic beam steering capability of the developed antenna, we synthesize a Mills-Cross composite aperture, forming a single-frequency all-electronic microwave camera.

We report here on an experimental investigation of the temporal behavior of transverse mode instabilities into “fully aperiodic large-pitch fibers” (FA-LPFs) operated in high-power continuous-wave laser configuration. To ensure an effective transverse single-mode emission into FA-LPFs, a perfect index matching between the active core and the background cladding materials (Δn=0) is required. The original design of such fibers enables an effective transverse single-mode emission by strengthening the higher-order mode delocalization out of the gain region, even for high heat load levels, consequently leading to the improvement of the beam spatial quality. The study was conducted over fibers of various gain region diameters, from 58 to 100 μm, for a refractive index mismatch Δn of about +8×10−5. The emitted beam is characterized using both M2 measurements and time traces to study the changeover of a stable temporal behavior to an unstable one.

We present the fabrication of multimaterial polarization maintaining optical fibers. We exploit the flexibility of the powder-in-tube process for fabricating silica-based optical fibers composed of two rods of glass material on the sides of the core. We demonstrate the capability of this process to use glass material with properties sorely different from the ones of silica for developing high-birefringence optical fiber. This proof-of-concept paves the way for the use of different materials with specific properties for improving the performances of polarization maintaining optical fibers.

International audience; We report on the first deep-ultraviolet/ultraviolet (DUV/UV) emission using a highly compact microwave-driven plasma-core photonic crystal fiber. The latter consists of a few centimeter long micro-plasma column of a gas mixture in the core of Kagome hollow-core photonic crystal fiber. The plasma is generated by nonintrusively exciting a ternary gas mixture of argon, nitrogen, and oxygen (Ar/N2/O2) with a microwave resonator. Several spectral lines in the wavelength range of 200–450 nm were produced, guided by an Ar-N2-O2 plasma-filled fiber, and controlled by simply varying the gas ratio of this gas mixture. An optimum gas mixture ratio was experimentally and theoretically identified for the strongest emission in the DUV range of 200–275 nm. The developed DUV emitting plasma-core fiber represents an important milestone towards the development of tunable and miniaturized DUV/UV laser sources.

Conventional microwave imaging schemes, enabled by the ubiquity of coherent sources and detectors, have traditionally relied on frequency bandwidth to retrieve range information, while using mechanical or electronic beamsteering to obtain cross-range information. This approach has resulted in complex and expensive hardware when extended to large-scale systems requiring ultrawide bandwidth. Relying on bandwidth can create difficulties in calibration, alignment, and imaging of dispersive objects. We present an alternative approach using an electrically-large, dynamically reconfigurable, metasurface antenna that generates spatially-distinct radiation patterns as a function of tuning state. The metasurface antenna comprises a waveguide feeding an array of metamaterial radiators, each of whose properties can be modified by applying a voltage to a diode integrated into the element. By deploying two of these apertures, one as the transmitter and one as the receiver, we realize sufficient spatial diversity to alleviate the dependence on frequency bandwidth and obtain both range and cross-range information using measurements at a single frequency. We demonstrate the method experimentally, using one-dimensional dynamic metasurface apertures and reconstructing various two-dimensional scenes (range and cross-range). Furthermore, we modify a conventional microwave imaging technique---the range migration algorithm---to be compatible with such configurations, resulting in an imaging system that is fast and simple in both software and hardware. The imaging scheme presented in this paper has broad application to radio frequency imaging, including security screening, through-wall imaging, biomedical diagnostics, and synthetic aperture radar.

International audience; Coherent combination of laser beams from 37 fiber amplifiers in a tiled aperture configuration has been achieved thanks to an innovative iterative process. The high efficiency as well as the speed of the phase control demonstrated the relevance of the method for phase locking of a large array of fiber lasers.

International audience; We demonstrate far-detuned parametric frequency conversion processes in a few mode graded-index optical fibers pumped by a Q-switched picosecond laser at 1064 nm. Through a detailed analytical and numerical analysis, we show that the multiple sidebands are generated through a complex cascaded process involving inter-modal four-wave mixing. The resulting parametric wavelength detuning spans in the visible down to 405 nm and in the nearinfrared up to 1355 nm.

Computational imaging modalities support a simplification of the active architectures required in an imaging system and these approaches have been validated across the electromagnetic spectrum. Recent implementations have utilized pseudo-orthogonal radiation patterns to illuminate an object of interest---notably, frequency-diverse metasurfaces have been exploited as fast and low-cost alternative to conventional coherent imaging systems. However, accurately measuring the complex-valued signals in the frequency domain can be burdensome, particularly for sub-centimeter wavelengths. Here, computational imaging is studied under the relaxed constraint of intensity-only measurements. A novel 3D imaging system is conceived based on 'phaseless' and compressed measurements, with benefits from recent advances in the field of phase retrieval. In this paper, the methodology associated with this novel principle is described, studied, and experimentally demonstrated in the microwave range. A comparison of the estimated images from both complex valued and phaseless measurements are presented, verifying the fidelity of phaseless computational imaging., 18 pages, 18 figures, article

International audience; We report on a high-performance curvature sensor based on a long-period grating (LPG) in a dual-concentric-core fiber (DCCF). The LPG is inscribed to couple light from the fundamental mode of the central core to the ring-core modes, resulting in the generation of a series of resonant dips. Two adjacent dips shift toward each other when the LPG is bent. By monitoring the variation of the wavelength interval between these two dips, this LPG can be applied in curvature measurement with a sensitivity as high as −9.046 nm/m−1. More importantly, such a wavelength interval is almost immune to the cross impacts of temperature and axial strain, since the sensitivities to temperature and axial strain are only 2.6 pm/°C and 0.083 pm/με, respectively.

International audience; Absorption of hydrogen gas (H2) in contact with palladium (Pd) makes Pd a material of choice for numerous H2 sensors. In this paper, we present the fabrication of optical fibers with embedded Pd particles in the silica cladding of the fibers. Fiber preforms prepared with a powder mixture of silica and palladium oxide (PdO) are heat-treated under specific conditions to reduce PdO to metallic Pd particles, dispersed in the silica matrix. Optical fibers with different topologies have been fabricated with lengths of several hundred meters and PdO concentration ranging from 0.01% to 5% mol (in addition to silica). Oxidation state, homogeneity, shape and size distribution of the particles embedded in the cladding of the preform and the fiber samples are studied with structural and micro-structural characterizations. Optical properties of the fibers are finally studied for evaluating the potential of this proof-of-concept work.

International audience; In the frame of sum frequency generation of a broadband infrared source, we aim to enlarge the converted bandwidth by using a pump frequency comb while keeping a high conversion efficiency. The nonlinear effects are simultaneously induced in the same nonlinear medium. In this paper, we investigate the spectral filtering effect on the temporal coherence behavior with a Mach-Zehnder interferometer using two pump lines. We show that joined effects of quasi-phase matching and spectral sampling lead to an original coherence behavior.

International audience; A laser based on a ribbon multicore ytterbium doped fiber where different cores amplified different spectral bands, has been mode-locked with a single saturable absorber mirror. Tunable dual wavelength synchronized picosecond pulses were obtained. Compensation of differential cavity roundtrip times was achieved in the fiber.

We describe the generation of powerful dispersive waves that are observed when pumping a dual concentric core microstructured fiber by means of a sub-nanosecond laser emitting at the wavelength of~1064 nm. The presence of three zeros in the dispersion curve, their spectral separation from the pump wavelength, and the complex dynamics of solitons originated by the pump pulse break-up, all contribute to boost the amplitude of the dispersive wave on the long-wavelength side of the pump. The measured conversion efficiency towards the dispersive wave at 1548 nm is as high as 50%. Our experimental analysis of the output spectra is completed by the acquisition of the time delays of the different spectral components. Numerical simulations and an analytical perturbative analysis identify the central wavelength of the red-shifted pump solitons and the dispersion profile of the fiber as the key parameters for determining the efficiency of the dispersive wave generation process., Comment: 11 pages, 12 figures

International audience; We report, for the first time to our knowledge, on a single-mode millijoule-level 100-nanosecond Er-doped fiber laser operating near 1550 nm. The system features a newly developed 35-μm-core Yb-free double-clad Er-doped fiber based on P2O5-Al2O3-SiO2 glass matrix and produces pulses with energy as high as 1 mJ at repetition rates of 1–10 kHz.

In the context of access networks, orthogonal frequency division multiplexing (OFDM) has been extensively studied for fiber-based optical communications. A DC-biased optical OFDM (DCO-OFDM) scheme (where no real constellation or Hermitian symmetry constraint is used), is proposed and explored for the first time, to the best of our knowledge, in an intensity modulated and direct detected (IM/DD) passive optical network (PON). In this paper, an analysis of the peak-to-average-power ratio and a discussion of the algorithm complexity are investigated. By means of numerical simulation in 12 Gb/s next-generation (NG)-PON1 OFDM with a split ratio of 1:64 users and 35 km reach, the new DCO-OFDM method is shown to achieve the same performance as the well-known conventional DCO-OFDM but with less computational complexity (gain of almost 54.3% on the required operations per bit). As a result, the new DCO-OFDM seems very interesting and a good candidate for NG-PON cost-sensitive applications, considering the implementation of real-time demonstrators including digital modulators and demodulators based on digital signal processing or a field-programmable gate array (FPGA).

International audience; Active coherent beam combination using a 7-non-coupled core,polarization maintaining, air-clad, Yb-doped fiber is demonstrated as amonolithic and compact power-scaling concept for ultrafast fiber lasers. Amicrolens array matched to the multicore fiber and an active phasecontroller composed of a spatial light modulator applying a stochasticparallel gradient descent algorithm are utilized to perform coherentcombining in the tiled aperture geometry. The mitigation of nonlineareffects at a pulse energy of 8.9 μJ and duration of 860 fs is experimentallyverified at a repetition rate of 100 kHz. The experimental combiningefficiency results in a far field central lobe carrying 49% of the total power,compared to an ideal value of 76%. This efficiency is primarily limited bygroup delay differences between cores which is identified as the maindrawback of the system. Minimizing these group delay issues, e.g. by usingshort and straight rod-type multicore fibers, should allow a practical powerscaling solution for femtosecond fiber systems.

The influence of post-sintering treatment by Hot Isostatic Pressing (post-HIP) of Nd:YAG ceramics on their sintering trajectories (grain size as a function of relative density or pore size) was evaluated and compared to trajectories obtained by solid-state reactive sintering (SSRS) under vacuum. This work shows that the separation phenomenon between pores and grain boundaries observed during SSRS can be efficiently avoided thanks to suitable post-HIP conditions. As a result, highly transparent Nd:YAG ceramics with small grain size (< 2 µm) were elaborated with limited sintering aid (SiO2) content.

International audience; Multi-wavelength operation of Q-switched Nd-doped YGd2Sc2Al2GaO12 garnet ceramic lasers has been investigated. Dual-wavelength emission around ~1.06 µm has been demonstrated both in the actively and passively Q-switched configurations. The ratio of output energy between the two laser wavelengths was driven by the temperature elevation caused by pumping. Passively Q-switched operation yields dual-frequency emission of two unsynchronized laser pulses carried by distinct transverse modes whereas active Q-switched configuration offers the possibility of synchronizing emission at the two wavelengths

International audience; Third-order sum frequency generation (TSFG) is one of the third-order nonlinear optical processes, and has the generation mechanism analogous to third harmonic generation (THG). By using a white-light supercontinuum, we can obtain broadband multiplex TSFG spectra. In the present study, we developed an electronically resonant TSFG spectrometer, and applied it to obtain TSFG spectra of hemoproteins. Analyzed TSFG ratio spectra clearly showed the resonant enhancement attributable to the electronic state of hemoproteins. This is a promising method for the imaging of electronic states of molecules inside living cells or tissues.

International audience; In this study, glass-compositional dependence of Tm3+ blue up-conversion photoluminescence (UCPL), which is known to be obtained via three-steps' energy transfers from Yb3+ to Tm3+ ions under near-infrared light excitation at ~980 nm, is investigated for Tm3+/Yb3+ co-doped TeO2-TlO0.5-ZnO glasses. The third step of energy transfer from Yb3+ to Tm3+ ions is particularly important ((Yb3+, Tm3+); (2F5/2, 3H4)→(2F7/2, 1G4)) since it determines the final blue UCPL intensity from 1G4 level compared to red and near-infrared UCPLs, and so then estimated with varied TlO0.5 and ZnO contents at the expense of TeO2 in the fixed Tm3+ and Yb3+ contents ([Yb3+]/[Tm3+] = 5). The substantial energy transfer rate (ETR) in the third step is evaluated from excitation power dependence of the blue UCPL intensity in comparison with near-infrared UCPL of Tm3+ ions with an aid of analytical method of PL lifetime and Judd-Ofelt theory. It is here revealed that the highest ETR is achieved to be 3.54 × 10−17 cm3/s for the glass composition of 70TeO2-10TlO0.5-19.4ZnO-0.1Tm2O3-0.5Yb2O3, and that the transfer rate is possibly related with the length of TeO2 glass network because a long tellurite glass network can cause segregation of rare-earth elements inducing effective Yb3+-Yb3+ energy migration and less quenching centers like dangling bonds of isolated TeO32-, resulted in the enhancement of the energy transfer for blue UCPL.

3; International audience; We generated a broad spectrum of light between 1064 and 1300 nm in the infrared by cascading stimulated Raman scattering in a potassium titanyl phosphate crystal while broadband conversion of the infrared Raman cascade was simultaneously achieved in the visible through second-harmonic generation (SHG) and sum-frequency mixing. We observed that odd- and even-order cascaded Stokes components were spatially addressed at different angles of propagation in the crystal. The efficiency of SHG and sum-frequency mixing is discussed as a function of the pump polarization. We also report on significant spatial distortions of the output Stokes beams. © 2013 Optical Society of America

International audience; Very large mode area, active optical fibers with a low high order mode content in the actively doped core region were designed by removing the inner cladding symmetry. The relevance of the numerical approach is demonstrated here by the investigation of a standard air-silica Large Pitch Fiber, used as a reference. A detailed study of all-solid structures is also performed. Finally, we propose new kinds of geometry for 50 μm core, all-solid microstructured fibers enabling a robust singlemode laser emission from 400 nm to 2200 nm.

International audience; We report experiments on a new laser architecture involving phase contrast filtering to coherently combine an array of fiber lasers. We demonstrate that the new technique yields a more stable phase-locking than standard methods using only amplitude filtering. A spectral analysis of the output beams shows that the new scheme generates more resonant frequencies common to the coupled lasers. This property can enhance the combining efficiency when the number of lasers to be coupled is large.

International audience; Direct amplification of output from chirped pulse oscillator (CPO) to 3.3 W of average power (pulse energy of 118 nJ in 20 ps pulse duration before compression) was achieved in a properly designed cladding pumped large mode area Er-doped fiber. Various configurations of CPO cavity with different FWHM of output spectrum and pulse duration were investigated. Fourier limit compression with 480 fs pulse duration and 32 kW peak power has been obtained for pulses with 14.8 nm FWHM spectrum. Subsequent nonlinear compression in a standard SMF-28 fiber yielded pulses as short as 145 fs.

International audience; We present high-resolution spectroscopy of I2 vapor that is loaded and trapped within the core of a hollow-core photonic crystal fiber (HC-PCF). We compare the observed spectroscopic features to those observed in a conventional iodine cell and show that the saturation characteristics differ significantly. Despite the confined geometry it was still possible to obtain sub-Doppler features with a spectral width of ∼6 MHz with very high contrast. We provide a simple theory which closely reproduces all the key observations of the experiment.

International audience; We have developed a new multimodal molecular imaging system that combines CARS (coherent anti-Stokes Raman scattering), SHG (second harmonic generation), THG (third harmonic generation) and multiplex TSFG (third-order sum frequency generation) using a subnanosecond white-light laser source. Molecular composition and their distribution in living cells are clearly visualized with different contrast enhancements through different mechanisms of CARS, SHG, THG and TSFG. A correlation image of CARS and TSF reveals that the TSF signal is generated predominantly from lipid droplets inside a cell as well as the peripheral cell wall.

International audience; The aim of this study is to combine multiple excitation wavelengths in order to improve accuracy of fluorescence characterization of labeled cells. The experimental demonstration is realized with a hematology analyzer based on flow cytometry and a CW laser source emitting two visible wavelengths. A given optical encoding associated to each wavelength allows fluorescence identification coming from specific fluorochromes and avoiding the use of noisy compensation method.

International audience; A specific scheme is used for fiber delivery of ultrashort pulses using conventional elements. Starting from a standard femtosecond Ti:Al2O3 oscillator (150 fs @ 830 nm), perfectly compressed ultrashort pulses with a duration of 45 fs are produced at the output of a standard two meter long single-mode fiber. The setup allows compensating independently and simultaneously second and third orders of chromatic dispersion as well as management of self-phase modulation in the fiber. It includes an optimized dispersion compensation line made of the assembly of diffraction gratings and prisms. The unsurpassed performances of the device are experimentally and numerically highlighted. Fiber delivery of sub-30 fs multinanojoule pulses is discussed.

International audience; We report co-phasing of 49 beams from a multicore fiber based on a spatial light modulator using a simple feedback loop control. A specific fiber of 7x7 Germanium doped cores was fabricated. The power carried by the far field main lobe of the phased array, in the continuous wave regime, amounts to 96% of its theoretical value. Femtoseconde pulses were also phase-locked with the same device configuration.

We experimentally demonstrate strong second-harmonic-generation from a self-induced all-optical poling in germanium-doped fiber with a subnanosecond laser pump at 1064 nm. The large second-harmonic conversion efficiency allows nonlinear spectral broadening at visible wavelengths so that up to nine distinct Raman sidebands have been obtained. In this work we emphasize how the Raman scattering, induced from the pump in the IR region, can drastically affect the optical poling effect, limiting in turn second-harmonic generation.

A new fabrication process of active optical silica glass based on direct sand vitrification is proposed. This method, an alternative to chemical vapor deposition (CVD), allows the fabrication of homogeneous and highly Yb(3+)-doped rods that are ten times larger in diameter than those produced by CVD. For large-mode-area fibers fabricated by the stack-and-draw method, this is a tremendous technical breakthrough that could offer great flexibility in fiber design. As a proof of concept, we focused here on the fabrication and characterization of active core material surrounded by pure silica. Consequently, we draw a simple multimode step-index fiber. The index ripple in the core that matches our objectives is approximately 2.2x10(-4). For this first demonstration, the core material is codoped with Yb(2)O(3) (3600 parts in 10(6)(ppm) by weight) and Al(2)O(3), yielding a 180 dB m(-1) absorption at a wavelength of 975 nm, whereas the background loss is around 0.8 dB m(-1). The continuous-wave laser obtained with this fiber exhibits 74% slope efficiency.

Phase locking of two fiber lasers is obtained by mutual injection. The coherence properties of this composite laser are analyzed. In the most general case, the radiations at the two output mirrors of the laser are not mutually coherent. The cross-correlation of the two emitted beams shows that an extra-cavity delay line is required to get stable and high visibility interference fringes. Such a laser configuration is attractive for coherent beam combining in the far field provided the multiple output beams are properly time delayed.

International audience; We present an Ytterbium fibre laser operating in the Q-switch regime by using a Micro- Opto- Electro- Mechanical System (MOEMS) of novel design. The cantilever-type micro-mirror is designed to generate short laser pulses with duration between 20 ns and 100 ns at repetition rates ranging from a few kilohertz up to 800 kHz. The bent profile of this new type of MOEMS ensures a high modulation rate of the laser cavity losses while keeping a high actuating frequency.

We report visible supercontinuum generation initiated by the second harmonic generation obtained in a germanium-doped microstructured optical fiber after optical poling processing. The visible spectral broadening is due to a cross-phase modulation effect between the generated IR solitons and the second harmonic (532 nm) of the 1064 nm pump wave. The 400-650 nm white-light emission is obtained on the fundamental propagation mode of the fiber.

International audience; We report on a mode-locked erbium-doped fiber laser suited to the generation of high-repetition-rate pulse trains or packets. The two-arm interferometer resonator performs a spectral filtering leading to the emission of short pulse packets with a high repetition rate, adjustable up to 200 GHz . A continuous pulse train with a repetition rate of up to 6.9 GHz was obtained by adding a recirculation loop inside the cavity to fill the spaces between all pulse packets.

We report what we believe to be the first experimental demonstration of ultrashort pulse characterization using fractional-order Fourier analysis. The analysis is applied to the interpretation of spectral interferometry resolved in time (SPIRIT) traces [which are spectral phase interferometry for direct electric field reconstruction (SPIDER)-like interferograms]. First, the fractional-order Fourier transformation is shown to naturally allow the determination of the cubic spectral phase coefficient of pulses to be analyzed. A simultaneous determination of both cubic and quadratic spectral phase coefficients of the pulses using the fractional-order Fourier series expansion is further demonstrated. This latter technique consists of localizing relative maxima in a 2D cartography representing decomposition coefficients. It is further used to reconstruct or filter SPIRIT traces.

International audience; We report smooth and broad continuum generation using a compact femtosecond Ti:Sapphire laser as a pump source and a tapered photonic crystal fibre as a nonlinear element. Spectral output is optimized for use in optical coherence tomography, providing a maximum longitudinal resolution of 1.5 µm in free space at 809 nm centre wavelength without use of additional spectral filtering.

Revisiting the pioneering work of Avizonis et al. [Appl. Phys. Lett. 31, 435 (1977)], we experimentally demonstrate that wave-front reversal of picosecond optical signals can be efficiently achieved with low-gain parametric amplification. The use of a KTP crystal permits forward phase conjugation of radiation with high divergence (40 mrad) and a broad spectrum (20 nm). The potential application of this technique to compensate for the group-velocity dispersion of standard optical fibers in the 1.55-microm window is discussed.

We report the experimental observation of the nonlinear interaction between two fundamental spatial solitons with a pi/2 phase difference in carbon disulfide. An energy flow from the phase-advanced soliton to the phasedelayed soliton was observed, which leads to a single self-trapped beam. The position of the output beam can be switched by reversing the sign of the solitons' initial phase difference.

International audience; In this paper, a multiscale monogenic analysis is applied to 2D interference fringe patterns. The monogenic signal was originally developed as a 2D generalization of the well-known analytic signal in the 1D case. The analytic and monogenic tools are both useful to extract phase information, which can then be directly linked with physical quantities. Previous studies have already shown the interest in the monogenic signal in the field of interferometry. This paper presents theoretical and numerical illustrations of the connection between the physical phase information and the phase estimated with the monogenic tool. More specifically, the ideal case of pure cosine waves is deeply studied, and then the complexity of the fringe patterns is progressively increased. One important weakness of the monogenic transform is its singularity at the null frequency, which makes the phase estimations of low-frequency fringes diverge. Moreover, the monogenic transform is originally designed for narrowband signals, and encounters difficulties when dealing with noised signals. These problems can be bypassed by performing a multiscale analysis based on the monogenic wavelet transform. Moreover, this paper proposes a simple strategy to combine the information extracted at different scales in order to get a better estimation of the phase. The numerical tests (synthetic and real signals) show how this approach provides a finer extraction of the geometrical structure of the fringe patterns.

International audience; We report experimental and numerical results that describe collisions between two-dimensional type II quadratic solitons excited in a KTP crystal by fundamental waves of orthogonal polarization. Our results provide experimental evidence of the possibility of both inelastic collision (when two quadratic solitons merge at input into a single soliton at output) and quasi-elastic collision.