Réal Vallée

Laval University, Québec, Quebec, Canada

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Publications (158)302.78 Total impact

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    ABSTRACT: Abstract
    Current Applied Physics 11/2014; 14(11):1531-1537. · 2.03 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). · 3.39 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). · 2.92 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
  • Optics letters. 07/2014; 39(13):3978-3981.
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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. · 3.39 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). · 3.39 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):2052-2055. · 3.39 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. · 3.39 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. · 3.39 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 01/2014; 333:133–138. · 1.44 Impact Factor
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    ABSTRACT: New glasses belonging to the NaF–Na2B4O7–WO3 system have been studied in order to inscribe optical waveguides within their volume through local refractive index modification after irradiation by ultrafast laser pulses. Appropriate addition of NaF to glasses belonging to the pseudo-binary vitreous system Na2B4O7–WO3 has allowed to obtain striae-free bulk glasses of large volume with high content of WO3 (35 mol%). Their physical and structural properties have been investigated through UV–visible spectroscopy, differential scanning calorimetry, densitometry and Raman spectroscopy. The glass of composition (NaF)15–(Na2B4O7)50–(WO3)35 has been then exposed to 800 nm femtosecond pulses of 70 fs width at a repetition rate of 100 kHz from a Ti-sapphire regenerative amplifier system. By varying the input pulse energy and scanning speed, homogeneous optical waveguides were inscribed and a positive refractive index change of the order of 5 × 10− 3 has been measured.
    Journal of Non-Crystalline Solids 01/2014; 385:153–159. · 1.72 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 01/2014; 105(13):131904-131904-4. · 3.79 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 01/2014; 324:245–251. · 1.44 Impact Factor
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    ABSTRACT: The technique of cathodic ac dual magnetron sputtering along with the high energy ionic bombardment is known to yield high quality thin films in terms of their uniformity and high density. This technique has been applied for the first time to achieve thermochromic VO2 thin films that show a high optical and electrical contrast between normal and switched states. In this two-step process Vanadium metal films were deposited and subsequently oxidized in optimum conditions to achieve stoichiometric VO2 films. Typical films switched between more than 40% to less than 5% transmission in the infrared region while undergoing an electrical sheet resistance change between 105 and 102 Ω/cm2. The application potential of such VO2 films in integrated optics is deemed high.
    ACS Applied Materials & Interfaces 11/2013; · 5.90 Impact Factor
  • David Hélie, Samuel Gouin, Réal Vallée
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    ABSTRACT: A novel method for assembling endcaps to optical fibers is presented. The method relies on femtosecond laser welding and milling of a glass slide to the polished end of the fiber. The fiber is welded to the glass slide in the cladding region so as to seal the core area without affecting its optical transparency. The same laser is used to mill through the glass slide thereby shaping a microscopic endcap with a diameter slightly larger than that of the fiber. The method was applied to both a standard and a microstructured optical fiber. Preliminary results are also presented on femtosecond laser welding parallel to an interface showing the potential of this approach for optical fiber fusion splicing.
    Optical Materials Express 10/2013; 3(10). · 2.92 Impact Factor
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    ABSTRACT: Thin films of GeAsS glass are prepared by e-beam evaporation technique. Photoinduced birefringence (PIB) is studied as function of the As content with concentrations ranging from 10% to 40%. Raman spectroscopy is used as additional tool to explain the corresponding changes undergone by the material system. The breakdown of homopolar bonds is suggested as a possible mechanism of photo induced structural changes leading to the creation of the PIB.
    Optical Materials Express 06/2013; 3(6). · 2.92 Impact Factor
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    ABSTRACT: We report a fiber strain sensor based on a single fiber Bragg grating (FBG) with a minimum detectable strain of 280 femtostrain/√Hz in the 20-kHz range. This breakthrough was made possible by operating the FBG on one of its slow-light peaks, and utilizing a FBG with a particularly low loss, fabricated using ultrafast pulses, to maximize the sensitivity. A theoretical and experimental noise analysis shows that the sensor noise is limited by laser frequency noise and not fiber phase noise, which suggests that even greater performance can be expected with a more stable laser frequency. © 2012 Optical Society of America
    Journal of Lightwave Technology 06/2013; 31(11):1804-1808. · 2.56 Impact Factor
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    ABSTRACT: The interaction of focused 800 nm femtosecond (fs) laser pulses at low (1–45 kHz) and moderate (50–250 kHz) repetition rates with fluoride (ZBLAN-type) bulk glass is investigated in detail. It is shown that at repetition rates lower than ~50 kHz and low pulse energies, the refractive index change induced by pulse filamentation is mainly negative at the irradiated zone. At repetition rates above 50 kHz, structures are formed as a result of the fs laser pulse induced heat accumulation and subsequent melting of the glass. The refractive index profile of the structures produced in this regime is influenced by the laser writing conditions (repetition rate, pulse energy and translation speed). It is shown that waveguides with large circular cross sections and smooth positive index changes can be formed through a precise control of glass exposure. Those waveguides can exhibit low propagation losses (~0.4–2 dB/cm) and are thus good candidates for the development of mid-IR integrated photonic devices. Both absorbed energy and repetition rate thresholds for heat accumulation are determined experimentally.
    Optical Materials Express 05/2013; 3(5):598. · 2.92 Impact Factor

Publication Stats

752 Citations
302.78 Total Impact Points

Institutions

  • 2003–2013
    • Laval University
      • • Department of Physics, Engineering Physics and Optics
      • • Center for Optics, Photonics and Lasers
      Québec, Quebec, Canada
  • 2012
    • L'Institut universitaire en santé mentale de Québec
      Québec, Quebec, Canada
  • 2004–2011
    • Université du Québec
      Québec, Quebec, Canada
    • University of Central Florida
      • Center for Research and Education in Optics and Lasers
      Orlando, FL, United States
  • 2007
    • National Optics Institute
      Québec, Quebec, Canada