Dominique Pagnoux

University of Limoges | UNILIM · Laboratoire XLIM

Coupled to endoscopic techniques, Mueller polarimetry has been proven to be promising for early detection of certain diseases which affect biological tissues of inner organs. However, the depolarization power which is one of the most informative polarimetric characteristics cannot be directly measured through a fiber endoscope. For evaluating this...

We report on a novel endomicroscope, to the best of our knowledge, designed for achieving full 4×4 Mueller polarimetric images of biological tissues through a fiber endoscope for medical diagnosis. The polarimetric technique is based on a previously published two-wavelength differential method (TWDM). A key component of the endomicroscope is a reso...

Nous présentons une source laser supercontinuum subnanoseconde émettant un spectre plat (< 0.02 dB/nm) sur une large bande de longueur d’onde [1100nm - 1650nm] avec une forte densité spectrale de puissance. Ce spectre est obtenu par cascade Raman en régime de dispersion normale dans une fibre optique monomode standard. Les caractéristiques de cette...

We introduce an experiment using electro-CARS, an electro-optical method based on the combination of ultrabroadband multiplex coherent anti-Stokes Raman scattering (M-CARS) spectroscopy and electric field stimulation. We demonstrate that this method can effectively discriminate the resonant CARS signal from the nonresonant background owing to a phe...

A supercontinuum laser source was designed for multiplex-coherent anti-Stokes Raman scattering spectroscopy. This source was based on the use of a germanium-doped standard optical fiber with a zero dispersion wavelength at 1600 nm and pumped at 1064 nm. We analyzed the nonlinear spectro-temporal interrelations of a subnanosecond pulse propagating i...

Propagation of light in multimode optical fibers usually gives a spatial and temporal randomization of the transmitted field similar to the propagation through scattering media. Randomization still applies when scattering or multimode propagation occurs in gain media. We demonstrate that appropriate structuration of the input beam wavefront can sha...

We experimentally demonstrate that pumping a graded-index multimode fiber with sub-ns pulses from a microchip Nd:YAG laser leads to spectrally flat supercontinuum generation with a uniform bell-shaped spatial beam profile extending from the visible to the mid-infrared at 2500 nm. We study the development of the supercontinuum along the multimode fi...

An optimized broadband source emitting from 1064 nm to 1600 nm was specially designed for CARS spectroscopy. This source is based on the use of a Ytterbium-doped photonic crystal fiber with a large core in which a supercontinuum is generated from a signal wave at 1064 nm regenerated by Ytterbium ions pumping. A particularly flat spectrum, with high...

The influence of a static electric field on a non-polar molecule has been studied by means of multiplex coherent anti-Stokes Raman scattering (M-CARS). A parallel measurement of electric field induced second harmonic generation (EFISHG) has also been led. Both techniques suggest a reorientation of the molecule due to the presence of an electric fie...

Particle size analyzers based on laser scattering commonly make use of light diffraction and scattering around the particle considered in its medium. For particle size below 50 μm, Fraunhofer theory must be abandoned in favor of Mie model, which requires to know the complex refractive index of both the particle and the medium. In this paper, we dem...

We demonstrate all-normal dispersion supercontinuum generation in the 1080 nm-1600 nm range by propagating subnanosecond pulses in a high numerical aperture standard optical fiber. The extreme saturation of the Raman gain provides a flat spectrum in the considered range, making this broadband source particularly suitable for coherent Raman spectros...

This paper reports a technique based on spectrally differential measurement for determining the full Mueller matrix of a biological sample through an optical fiber. In this technique, two close wavelengths were used simultaneously, one for characterizing the fiber and the other for characterizing the assembly of fiber and sample. The characteristic...

Selon un aspect, l'invention concerne un dispositif de caractérisation polarimétrique déportée (100) d'un échantillon (S). Il comprend une source d'émission (10) d'au moins une onde lumineuse incidente à au moins une première longueur d'onde (λE) ; une fibre optique monomode (30) dans laquelle l'onde lumineuse incidente est destinée à se propager;...

Nous présentions une source de continuum infrarouge optimisée pour la micro-spectroscopie Raman cohérente (CARS) de cellules biologiques. Elle est conçue de façon à émettre une forte densité spectrale de puissance dans la bande correspondant à la zone d'empreinte digitale des liaisons chimiques d'intérêt (1080-1600 nm pour un pompage à 1064 nm) tou...

Nous avons montré qu'un refroidissement moléculaire pouvait être induit par un champ électrique statique appliqué à des molécules non polaires d'huile de paraffine. Cet effet a été mis en évidence grâce à une mesure de spectroscopie CARS (Coherente Anti-Stokes Raman Scattering). De manière complémentaire, l'exposition de molécules à un champ électr...

We report a novel technique for polarimetric characterization of samples through a flexible fiber endoscope, with a single shot measurement per pixel. The sample is simultaneously probed with a large diversity of polarization states, and both degree of polarization and linear retardance are determined thanks to specific processing of data. The prob...

A novel technique to measure the full 4 × 4 Mueller matrix of a sample through an optical fiber is proposed, opening the way for endoscopic applications of Mueller polarimetry for biomedical diagnosis. The technique is based on two subsequent Mueller matrices measurements: one for characterizing the fiber only, and another for the assembly of fiber...

The invention relates to a method and to a device for determining at least one piece of polarization information on a measurement point of a target sample, the device comprising:—a light source capable of emitting a rectilinearly polarized light beam, the light beam being intended to be reflected by the measurement point;—a means for computing pola...

Broadband frequency doubling of an infrared supercontinuum is demonstrated. This unconventional Second Harmonic Generation process is obtained in a PPLN crystal excited along its Z axis, thanks to nonlinear Cerenkov and Raman-Nath interactions.

We present experimental results on microwave assisted Multiplex Coherent Anti-Stokes Raman Spectroscopy (M-CARS) measurements in liquids. The applied nanosecond electric field allows M-CARS signal enhancement and offers potentialities to remove non resonant background. OCIS codes: (180.4315) Nonlinear microscopy; (250.0250) Optoelectronics; (250.67...

we present very first measurements of Mueller matrices of samples through an optical fiber, opening the way to endoscopic applications for early detection of diseases. The technique is based on measurements of both the single fiber and the assembly fiber+sample Mueller matrices. The 2m optical guide is made of two identical pieces of PM fiber splic...

The invention relates to a method and to a device for determining a piece of polarisation information on a measurement point of a target sample, the device comprising: —a light source capable of emitting a rectilinearly polarised light beam in a predefined direction, the light beam being intended to be reflected by the measurement point of the targ...

Recently, polarimetric imaging of biological tissues has been shown to be a very promising technique for early detection of diseases such as lung, skin or colon cancer. In order to apply polarization imaging to deep organs in situ, this technique must be associated to endoscopic ones. In this case, light reflected by the targeted area ("sample") is...

Multiplex-Coherent Anti Stokes Raman Scattering (M-CARS) microscopy is of great interest for vibrational imaging of biological cells [1,2] or chemical sample with high sensitivity [3]. In this paper, we present a new broadband laser source for applications in multimodal nonlinear imaging including Second Harmonic Generation (SHG), Sum Frequency Gen...

In this communication, we present a novel hybrid Q-switched laser source designed to emit short pulses with high peak power and low timing jitter at increased repetition rate, for LIDAR, CARS microscopy or flow cytometry applications.

Autre référence de publication : US20120170606 / Classification internationale : H01S 3/117; H01S 3/108; H01S 3/113; H01S 3/082; H01S 3/23; H01S 3/06 - Classification européenne : H01S 3/082

Autre référence de publication : US20120177070 / Classification internationale : H01S 3/30; H01S 3/06; H01S 3/117; H01S 3/082; H01S 3/108; H01S 3/113 - Classification européenne : H01S 3/082

We present a novel Q-switched laser source using a micro-optical-electromechanical mirror (MOEM) designed for short pulse emission. It is based on a hybrid configuration including a passively Q-switched microchip laser coupled to a fiber cavity closed by a cantilever type MOEM acting as an active modulator. This specially designed mirror with a sin...

We report the design of low-cost and compact short-pulse source based on a fiber-coupled Q-switched microchip laser. The combination of stimulated Raman scattering and nonlinear polarization rotation effects in the fiber associated with appropriate filtering makes it possible to tune pulse duration down to 32 ps with peak power above 3 kW. Pulse to...

We present a novel broadband laser source based on a dual cavity in which a subnanosecond passively Q-switched microchip laser is coupled with a long cavity including an acousto-optic modulator (AOM) and a microstructured optical fiber working as a non linear medium. This active-passive Q-switched laser source emits pulses as short as those emitted...

Article de vulgarisation scientifique

We report on a fiber laser configuration, emitting two phase-locked and single mode beams at the output of two multicore fibers. The passive technique is based both on the selective excitation of the only in-phase supermodes of the multicore fibers and on an intra-cavity angular filtering of the emitted beams to provide phase control. As a proof of...

We propose a new method to control the mode combination at the output of a 19-core fiber laser in order to produce a bright beam with uniform phase. The technique is based on both the selective excitation of the amplifying multicore fiber and on an intra-cavity angular filtering at the output. The excitation of the fundamental in-phase supermode of...

We report on a polarization imaging device which probes a remote sample through a flexible standard single-mode fiber. Both polarized laser source and polarization analysis system are set on one side of the fiber, the object of interest being probed by the beam exiting at the opposite end. Phase retardation and polarization rotation angle due to ei...

We report the possibility of using nonuniform tapered microstructured optical fiber (NTMOF) to reduce the overall coupling loss from an upstream MOF to a downstream fiber being another MOF with different geometry. The NTMOF is supposed to be drawn at the output end of the upstream MOF, with no coupling loss between the two. The propagation loss alo...

The main modelling methods devoted to microstrutured air-silica optical fibres (MOFs) are presented and discussed. Then, the specific propagation properties of MOFs are studied in detail. Characteristics measured on fibres manufactured in our laboratory or reported in the literature are analysed. A large number of potential and demonstrated applica...

Introduction Two guiding principles in microstructured fibers Manufacture of microstructured fibers Modeling TIR-MOFs Main properties and applications of TIR-MOFs Photonic bandgap fibers Conclusion References

We present a new cavity design for controlling the spatial quality of the beam delivered by a fibre laser including a multicore fibre. A quasi Gaussian profile is produced at the 7-core fibre output involving self-imaging effects in the multicore fibre and spatial filtering. Numerical and experimental investigations analyse the spatial and spectral...

Polarization images were obtained using a flexible optical fiber device. The endoscopic technique is based on the real-time compensation of the birefringence of the standard fiber by means of a miniaturized Faraday rotator. Based on a Jones formalism analysis, specific signal processing allows one to extract both the phase retardation and the degre...

We have reported a polarization maintaining multicore air/silica optical fiber. Such a fiber can serve as an image guide for laser scanning endoscopy. We designed and fabricated a series of multicore fiber with a square lattice and non coupled individual cores. Air/silica structures provide the possibility of combining large numerical aperture, and...

We take advantage of nonlinear effects in a low birefringence fiber to reshape subnanosecond laser pulses. Both polarization and spectral modulation allow pulse shortening by a factor higher than 10 in the normal dispersion regime.

Taking advantage of the combination of stimulated Raman scattering and nonlinear polarization rotation in a single-mode optical fiber, a temporal reshaping of subnanosecond pulses is achieved by means of both spectral and polarization filtering. Shortening of 650 ps down to 43 ps temporally and spectrally stable pulses is experimentally obtained. N...

The origin and the behavior of the birefringence of solid-core air-silica microstructured fibers is described with the help of a simple approximate model. The first two modes of three different types of fibers are studied. Numerical results, obtained from both finite element and boundary integral methods calculations, are presented to support the v...

For the first time polarization images using an endoscopic technique are reported. Images based on the degree of polarization measurement allow to discriminate sound and degraded regions in a type I collagen sample.

The origin and the behavior of the birefringence of solid-core air-silica microstructured fibers is described with the help of a simple approximate model. The first two modes of three different types of fibers are studied. Numerical results, obtained from both finite element and boundary integral methods calculations, are presented to support the v...

We demonstrate that the resonance wavelength of fiber Bragg gratings photowritten in the core of microstructured optical fibers can be efficiently stabilized versus temperature by inserting suitable refractive index materials with a negative thermal sensitivity into the holes. By these means, the effective index of the guided mode undergoes thermal...

We propose new laser architecture to improve the spatial emission of a multimode fibre amplifier (MMFA) by using a self-imaging process. Interference between the different modes of the MMFA is filtered by a single-mode fibre section which serves as feedback in a unidirectional ring cavity. The laser self-adjusts its frequency to ensure self-imaging...

A temporal shortening by a factor higher than 10 of subnanosecond pulses launched into a low-birefringence optical fiber is achieved by polarization filtering at the output. By means of the theoretical approach, in good agreement with experimental measurements, the impact of the nonlinear polarization rotation and of the coherent coupling phenomena...

The thermal drift of the characteristic wavelength of fiber Bragg gratings (FBGs) photowritten in the core of microstructured fibers (MOFs) is significantly reduced by inserting a liquid of suitable refractive index into their holes. For instance, the spectral range of variations is divided by a factor of 4 over a temperature range larger than 20de...

The azimuthal far-field analysis technique (AFFAT) is one of the only two methods reported to date, able to measure the cutoff wavelength λc in microstructured fibres (MOFs). The measurement is operated through a parameter D which is related to the modulation of the power crossing a rotating slit at the output of the tested fibre. In standard fibre...

In the preceding chapters, photonic crystals have been essentially considered as (quasi) periodic ensembles of dielectric elements, which allow the control of the propagation of light through the effects of photonic band gaps and transmission bands. It might be pointed out, however, that the first periodic (one, two and three-dimensional) ensembles...