Réal Vallée

Laval University, Quebec City, Quebec, Canada

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Publications (175)329.8 Total impact

  • K. Palanjyan, R. Vallée, T. Galstian
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    ABSTRACT: Photoinduced birefringence (PIB) is studied in thin films of Ge25As30S45 glass prepared by e-beam evaporation technique. Excitation of the material is done in air at 514.5 nm and the PIB is monitored with a He-Ne laser at 632.8nm (incident from the same side). Based on the obtained experimental results, we show that the local value of PIB in this material can reach a value of ≈0.11, which is, to the best of our knowledge, the highest value ever reported in the literature.
    Optical Materials Express 05/2015; 5(5). DOI:10.1364/OME.5.001122 · 2.92 Impact Factor
  • K. Palanjyan, R. Vallée, T. Galstian
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    ABSTRACT: Photo-induced anisotropy phenomena have been investigated in Ge25As30S45 chalcogenide glassy thin-films prepared by the electron beam evaporation technique. Thin-films of thicknesses ranging from 3 to 7 μm were prepared, annealed slightly below the glass transition temperature Tg and characterized by means of optical transmission, thermal analysis, elemental microanalysis through energy dispersive X-ray spectroscopy and by micro-Raman spectroscopy. Photo-induced dichroism (PID) was studied using band gap 514 nm laser excitation. Its kinetics was studied by observing the transmission and reflection of the film at different excitation intensities and temperatures. The conversion of heteropolar (Ge–S, As–S) toward homopolar (Ge–Ge, As–As) bonds was confirmed by polarized micro-Raman spectroscopic studies.
    Journal of Non-Crystalline Solids 02/2015; 410. DOI:10.1016/j.jnoncrysol.2014.12.004 · 1.72 Impact Factor
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    ABSTRACT: Single-frequency laser emission from a distributed feedback all-fiber laser operating in the vicinity of 3 μm is demonstrated. The laser cavity was made of a 30 mm long π-phase-shifted fiber Bragg grating inscribed in a heavily erbium-doped fluoride fiber using infrared femtosecond pulses and the dithering phase-mask technique. A maximum CW output power of 12 mW was obtained at 2794.4 nm by using a multimode pumping scheme. The narrow linewidth was characterized to be lower than 20 kHz using a heterodyne technique. This achievement represents a significant step toward the development of active frequency references operating in the mid-infrared.
    Optics Letters 01/2015; 40(1). DOI:10.1364/OL.40.000081 · 3.18 Impact Factor
  • Ali Saliminia, Antoine Proulx, Réal Vallée
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    ABSTRACT: We demonstrate our experimental results on inscription of strong first-order Bragg gratings in hydrogen-free and hydrogen-loaded pure silica photonic crystal fibers (PCFs) using high-intensity 160 femtosecond (fs) UV laser pulses at 266 nm and a two-beam Talbot interferometer. Bragg reflectivities up to 37 dB for the H2-loaded fiber as well as Bragg wavelength tuning over the telecom C-band using a single phase mask were achieved. The in-situ nonlinear filamentation of UV fs laser pulses, scattered by the fiber’s micro-structured cladding, is demonstrated by direct refractive index profile measurement across the cross section of a written fiber. The results of thermal annealing measurements for a H2-loaded PCF are also presented.
    Optics Communications 11/2014; 333:133–138. DOI:10.1016/j.optcom.2014.07.069 · 1.54 Impact Factor
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    ABSTRACT: We report on infrared supercontinuum (SC) generation through laser filamentation and subsequent nonlinear propagation in a step-index As<sub>2</sub>S<sub>3</sub> fiber. The 100 μm core and high-purity As<sub>2</sub>S<sub>3</sub> fiber used exhibit zero-dispersion wavelength around 4.5 μm, a mid-infrared background loss of 0.2 dB/m, and a maximum loss of only 0.55 dB/m at the S-H absorption peak around 4.05 μm. When pumping with ultrashort laser pulses slightly above the S-H absorption band, broadband infrared supercontinua were generated with a 20 dB spectral flatness spanning from 1.5 up to 7 μm. The efficiency and spectral shape of the SC produced by ultrashort pulses in large-core As<sub>2</sub>S<sub>3</sub> fiber are mainly determined by its dispersion, the S-H contaminant absorption, and the mid-infrared nonlinear absorption.
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    ABSTRACT: We report on infrared supercontinuum (SC) generation through laser filamentation and subsequent nonlinear propagation in a step-index As2S3 fiber. The 100 μm core and high-purity As2S3 fiber used exhibit zero-dispersion wavelength around 4.5 μm, a mid-infrared background loss of 0.2 dB/m, and a maximum loss of only 0.55 dB/m at the S-H absorption peak around 4.05 μm. When pumping with ultrashort laser pulses slightly above the S-H absorption band, broadband infrared supercontinua were generated with a 20 dB spectral flatness spanning from 1.5 up to 7 μm. The efficiency and spectral shape of the SC produced by ultrashort pulses in large-core As2S3 fiber are mainly determined by its dispersion, the S-H contaminant absorption, and the mid-infrared nonlinear absorption.
    Optics Letters 11/2014; 39(22). DOI:10.1364/OL.39.006474 · 3.18 Impact Factor
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    ABSTRACT: Abstract
    Current Applied Physics 11/2014; 14(11):1531-1537. DOI:10.1016/j.cap.2014.09.005 · 2.03 Impact Factor
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    ABSTRACT: The photosensitivity of GeSx binary glasses in response to irradiation to femtosecond pulses at 800 nm is investigated. Samples with three different molecular compositions were irradiated under different exposure conditions. The material response to laser exposure was characterized by both refractometry and micro-Raman spectroscopy. It is shown that the relative content of sulfur in the glass matrix influences the photo-induced refractive index modification. At low sulfur content, both positive and negative index changes can be obtained while at high sulfur content, only a positive index change can be reached. These changes were correlated with variations in the Raman response of exposed glass which were interpreted in terms of structural modifications of the glass network. Under optimized exposure conditions, waveguides with positive index changes of up to 7.8x10−3 and a controllable diameter from 14 to 25 μm can be obtained. Direct inscription of low insertion losses (IL = 3.1 – 3.9 dB) waveguides is demonstrated in a sample characterized by a S/Ge ratio of 4. The current results open a pathway towards the use of Ge-S binary glasses for the fabrication of integrated mid-infrared photonic components.
    Optics Express 10/2014; 22(21):26103-16. DOI:10.1364/OE.22.026103 · 3.53 Impact Factor
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    ABSTRACT: We investigated the influence of silver ions during the direct femtosecond laser-induced formation of nanogratings (NGs) at the surface of a tailored sodium gallophosphate glass. We observed that the silver ions had a remarkable influence because the silver-containing glass showed (1) lower fluence thresholds for the formation of the NGs; (2) much smoother NG shapes; and (3) a bifunctional behavior because fluorescence from laser-induced silver clusters occurs prior to the formation of the NGs. We demonstrate for the first time, to our knowledge, the formation of NGs assisted by noble metal ions, such as ions playing a kind of catalytic-like role that enhances and improves the NG formation and its incubation process. Our innovative approach provides promising potential for further improvements in processes for NG formation.
    Optics Letters 10/2014; 39(19). DOI:10.1364/OL.39.005491 · 3.18 Impact Factor
  • Feng Liang, Real Vallee
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    ABSTRACT: We present a comprehensive analysis of physical evolution of nanograting formation based on an experiment performed with femtosecond pulses focused under moderate focusing conditions and where pulse energy is slowly increased as the focused beam is moved along the sample surface. The results demonstrate that nanograting inscription is initiated at the location of the maximum plasma density and evolves through local intensity side lobes, whose locations are self-regulated in a closed feedback loop, in agreement with the plasmonic model.
    Applied Physics Letters 09/2014; 105(13):131904-131904-4. DOI:10.1063/1.4896749 · 3.52 Impact Factor
  • Ali Saliminia, Réal Vallée
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    ABSTRACT: We present the fabrication and characterization of strong first-order Bragg gratings operating around 1550 nm in standard telecom fibers (SMF-28) by use of 160 fs UV laser pulses at 266 nm and a Talbot interferometer. Bragg reflectivities exceeding 50 dB are achieved in both hydrogen-free and hydrogen-loaded fibers. In addition, Bragg wavelength tuning over the telecom C-band using a single phase mask is demonstrated. We also show that the formation of Bragg gratings, relying on a two-photon absorption process, is intimately accompanied by the optical filamentation process of UV fs laser pulses during nonlinear propagation in the fiber.
    Optics Communications 08/2014; 324:245–251. DOI:10.1016/j.optcom.2014.03.068 · 1.54 Impact Factor
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    ABSTRACT: The fabrication process and characterization of composite step-index fibers with a large refractive index difference (Δn = 0.336 at 1.54 μm) between the tellurite glass-made core and the germanate-tellurite glass-made cladding are presented. In order to fabricate these composite fibers, the composition of the cladding glass was selected because of its thermal and optical properties corresponding to those of the core glass. This work demonstrates that even if these two glasses have relatively different chemical compositions, their association results in a good quality fiber. This fiber design combines strong confinement of the optical modes inside its core and good environmental stability for nonlinear applications in the mid-infrared.
    Optical Materials Express 08/2014; 4(8). DOI:10.1364/OME.4.001740 · 2.92 Impact Factor
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    ABSTRACT: We report a record group delay of 19.5 ns (an equivalent group index of 292) measured in a strongly apodized, 2 cm long, femtosecond fiber Bragg grating (FBG). This significant (similar to 4-fold) improvement over the previous record results from the presence of a Fabry-Perot arising from the apodization. The measured group-index spectrum is well explained by a model that accounts for the apodized profiles of the index modulation, propagation loss, and birefringence of the grating. The peak power loss inferred from this model is only similar to 0.12 m(-1), which is one of the lowest values reported for an FBG. (C) 2014 Optical Society of America
    Optics Letters 07/2014; 39(13):3978-3981. DOI:10.1364/OL.39.003978 · 3.18 Impact Factor
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    ABSTRACT: Recent advances in the development of mid-infrared Bragg grating-based fiber lasers will be reviewed. A 30W-level erbium-doped fluoride fiber laser emitting in the vicinity of 3 μm will be detailed. It will be shown that such high power fiber laser can also be used as a pump source to generate a laser emission between 3 and 4 μm through stimulated Raman scattering in chalcogenide glass fibers.
    Photonics Society Summer Topical Meeting Series, 2014 IEEE; 07/2014
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    ABSTRACT: We report that by using 800 nm femtosecond pulses and the phase-mask technique, first-order fiber Bragg gratings with refractive index modulation in excess of 1×10−3 can be written through both the acrylate and polyimide coatings of unloaded standard silica fibers without noticeable degradation of mechanical strength. We also demonstrate that the same experimental conditions can be applied for efficient FBG writing through the polyimide coating of pure silica core fibers, opening significant opportunities in the field of fiber sensors.
    Optics Letters 06/2014; 39(12):3646-3649. DOI:10.1364/OL.39.003646 · 3.18 Impact Factor
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    ABSTRACT: The performance of mode-locked fiber ring lasers incorporating two opposite-dispersion chirped fiber Bragg gratings is presented in different dispersion regimes. Pulses of nanojoule energy and duration well below 100 fs are generated.
    CLEO: Science and Innovations; 06/2014
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    ABSTRACT: We report the first stable mode-locking from an Er3+: fluoride glass fiber laser linear cavity operating near 3 μm to the best of our knowledge. The linear cavity includes a saturable absorber mirror and a fiber Bragg grating to provide a controlled and wavelength selective feedback. The pulse train has a 51.75 MHz repetition rate, an estimated 60 ps pulse duration, and an average power of 440 mW. The stable and self-starting mode-locking regime is confirmed by RF spectral measurements and is maintained over several hours.
    Optics Letters 06/2014; 39(11). DOI:10.1364/OL.39.003294 · 3.18 Impact Factor
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    ABSTRACT: Laser emission is demonstrated at a wavelength of 3.766 μm in a cascaded Raman gain device. The laser cavity is made of two nested pairs of fiber Bragg gratings inscribed in a 2.8 m length of low-loss As2S3 fiber. An erbium-doped fluoride glass quasi-CW fiber laser emitting at 3.005 μm is used to pump the cascaded Raman cavity, which converts the pump wavelength successively to the first and second Stokes orders, respectively at 3.340 and 3.766 μm. A laser output peak power in excess of 100 mW is obtained with a lasing efficiency of about 8.3% with respect to the launched pump power. This represents the highest emission wavelength delivered by a fiber laser operating at room temperature.
    Optics Letters 04/2014; 39(7-7):2052-2055. DOI:10.1364/OL.39.002052 · 3.18 Impact Factor
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    ABSTRACT: Laser emission is demonstrated at a wavelength of 3.766 μm in a cascaded Raman gain device. The laser cavity is made of two nested pairs of fiber Bragg gratings inscribed in a 2.8 m length of low-loss As<sub>2</sub>S<sub>3</sub> fiber. An erbium-doped fluoride glass quasi-CW fiber laser emitting at 3.005 μm is used to pump the cascaded Raman cavity, which converts the pump wavelength successively to the first and second Stokes orders, respectively at 3.340 and 3.766 μm. A laser output peak power in excess of 100 mW is obtained with a lasing efficiency of about 8.3% with respect to the launched pump power. This represents the highest emission wavelength delivered by a fiber laser operating at room temperature.
    Optics Letters 04/2014; 39(7):2052-5. · 3.18 Impact Factor
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    ABSTRACT: By incorporating two linearly chirped ultrabroadband fiber Bragg gratings of opposite dispersion in an all-fiber ring laser, we demonstrate a mode-locking regime in which a femtosecond pulse evolving in the normal dispersion gain segment is locally transformed into a highly chirped picosecond pulse that propagates in the remaining section of the cavity. By minimizing nonlinear effects and avoiding soliton pulse shaping in this anomalous-dispersion section, low repetition rate fiber lasers can be made to produce high-energy ultrashort pulses. Using this approach, 98 fs pulses with 0.96 nJ of energy are obtained from an erbium-doped fiber laser operated in the highly anomalous dispersion regime at a repetition rate of 9.4 MHz.
    Optics Letters 02/2014; 39(4):989-92. DOI:10.1364/OL.39.000989 · 3.18 Impact Factor

Publication Stats

1k Citations
329.80 Total Impact Points

Institutions

  • 1997–2015
    • Laval University
      • • Department of Physics, Engineering Physics and Optics
      • • Center for Optics, Photonics and Lasers
      Quebec City, Quebec, Canada
  • 1996–2015
    • Université du Québec
      Quebec City, Quebec, Canada
  • 2012
    • L'Institut universitaire en santé mentale de Québec
      Québec, Quebec, Canada
  • 2003–2004
    • University of Central Florida
      Orlando, Florida, United States