Réal Vallée

Laval University, Quebec City, Quebec, Canada

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Publications (187)341.29 Total impact

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    ABSTRACT: Abstract
    Optical Materials 09/2015; 47:518-523. DOI:10.1016/j.optmat.2015.06.032 · 2.08 Impact Factor
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    Optics Letters 06/2015; 40(12):2882-2885. DOI:10.1364/OL.40.002882 · 3.18 Impact Factor
  • Vincent Fortin, Martin Bernier, Réal Vallée
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    ABSTRACT: Recent advances in high power erbium-doped fluoride fiber lasers near 2.94 μm are reviewed. Based on an all-fiber architecture, a 20 W record output power was achieved at this wavelength of interest for medical applications.
    CLEO: Science and Innovations 2015, San Jose, California, United States; 05/2015
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    ABSTRACT: We report a tunable single-frequency laser emission near 2.8 μm from an all-fiber distributed feedback laser. A 20 kHz linewidth is measured with a tunability of ~1 nm at a step resolution of 3 pm.
    CLEO: Science and Innovations 2015, San Jose, California, United States; 05/2015
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    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: Ultrafast fiber lasers operating in the near-infrared have revolutionized laser science by enabling numerous breakthroughs in both fundamental science and industrial applications. In this Letter, we extend the spectral coverage of these laser sources to the mid-infrared by reporting the first femtosecond fiber laser operating near 3 μm. This passively mode-locked fiber ring laser based on nonlinear polarization evolution in an Er3+-doped fluoride glass fiber generates 207 fs pulses at 2.8 μm with an estimated peak power of 3.5 kW. This demonstration paves the way for further developments of promising applications in the molecular fingerprint region such as frequency comb spectroscopy.
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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: VO2 thin films were fabricated by argon ion beam assisted non-reactive ac dual magnetron sputtering followed by carefully controlled thermal oxidation. This method is known to give high quality compact thin films with uniform high deposition rates. Thin films deposited on both bare glass and indium tin-oxide (ITO) coated glass substrates were studied, respectively, as passive and active thermochromic devices for their electrical and optical switching behaviors. Thin films varying in thicknesses from 65 to 250 nm were investigated. ITO film was used as an integrated heating device to activate the phase transition via an applied bias voltage. Such structures were found to bear several advantages from an application point of view.
    Current Applied Physics 11/2014; 14(11-11):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
  • K. Palanjyan, R. Vallée, T. Galstian
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    ABSTRACT: We describe the photo induced formation of gradient index (GRIN) lenses in thin films of chalcogenide glass (ChG) of Ge25As30S45 composition. We examine the changes of thickness of these samples by DekTak profilometry, as well as the optical performance and wave front distortions of the obtained lenses by using a Shack Hartmann sensor. The GRIN formation is related to the photo induced shift of the band gap towards shorter wavelengths (so-called photo-bleaching effect). The corresponding photo-induced birefringence of this material is in the origin of anisotropic GRIN lenses formed [1].
    Photonics North 2014; 09/2014
  • K. Palanjyan, R. Vallée, T. Galstian
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    ABSTRACT: We have studied thin films of Ge25As30S45 glass evaporated by electron-beam technique. We have analyzed the transmission spectra of thin films of the same nominal composition, obtained under identical conditions, but with four different thicknesses varying from 1 to 7 micrometers. All fabricated films were annealed for 1h at 300 degrees C (below the glass transition temperature of this glass). As a result, we observed a thickness dependent blue-shift of about 100 nm of their transmission edge. We have calculated the optical band gap of those annealed thin films and we have observed that the slope of absorption edge becomes less abrupt and the band gap decreases when their thickness increases. Furthermore, this band gap decrease is accompanied with a broadening of the tails and localized states, which indicates an increase of the degree of disorder in the vitreous network. This could be explained by the higher density of defects and dangling bonds in the thinner films since the amount of deposited material is smaller. This implies therefore an increase of both the degree of disorder and the concentration of defects, and consequently the decrease of the optical gap.
    Photonics North 2014; 09/2014
  • 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

Publication Stats

1k Citations
341.29 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
  • 1996–2014
    • Université du Québec
      Québec, Quebec, Canada
  • 2012
    • L'Institut universitaire en santé mentale de Québec
      Québec, Quebec, Canada
  • 2003–2004
    • University of Central Florida
      Orlando, Florida, United States