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  • 1. Albert, Jacques
    et al.
    Fokine, Mikael
    KTH, Superseded Departments, Physics.
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Grating formation in pure silica-core fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 10, p. 809-811Article in journal (Refereed)
    Abstract [en]

    Strong grating formation in pure silica-core fibers by use of 193-nm ArF-laser radiation is reported. Unsaturated refractive-index changes of Deltan similar to 0.3 X 10(-3) were observed in nontreated fiber, and changes of Deltan similar to 0.5 X 10(-3) were observed in fibers with a high hydroxyl concentration. Possible mechanisms of photosensitivity in pure silica-core fibers are discussed.

  • 2. Camara, A. R.
    et al.
    Gouvêa, P. M. P.
    Brolo, A. G.
    Fan, M.
    Abel, R.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Braga, A. M. B.
    Carvalho, I. C. S.
    LSPR-based fiber optic sensing with chemically deposited Au nanoparticles2010In: Latin America Optics and Photonics Conference (LAOP) 2010, 2010Conference paper (Refereed)
    Abstract [en]

    A refractive index fiber optic sensor based on Localized Surface Plasmon Resonance (LSPR) and specular reflection from chemically deposited gold nanoparticles has been characterized, presenting a sensitivity of 38 nm/RIU.

  • 3.
    Canalias, Carlota
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Backward quasi phase matched second harmonic generation in sub-micron periodically poled KTiOPO42006In: CLEO/QELS 2006, Optical Society of America, 2006Conference paper (Refereed)
    Abstract [en]

    1mm thick KTiOPO4 was poled with 720nm domain period by employing UVlithography, chemical patterning and electric field poling. The structure was used to demonstrate 6 and 7 order quasi-phase matched backward second harmonic generation.

  • 4.
    Canalias, Carlota
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Physics.
    Backward quasi phase matched second harmonic generation in sub-micron periodically poled KTiOPO42005In: 2005 Conference on Lasers & Electro-Optics (CLEO), Vols 1-3, WASHINGTON: OPTICAL SOC AMERICA , 2005, p. 2264-2266Conference paper (Refereed)
    Abstract [en]

    1mm thick KTiOPO4 was poled with 720nm domain period by employing UV-lithography, chemical patterning and electric field poling. The structure was used to demonstrate 6 and 7 order quasi-phase matched backward second harmonic generation.

  • 5.
    Canalias, Carlota
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Backward quasi-phase-matched second-harmonic generation in submicrometer periodically poled flux-grown KTiOPO42005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, no 18, p. 181105-1-181105-3Article in journal (Refereed)
    Abstract [en]

    A 1 turn thick flux-grown KTiOPO4 sample was poled with a 720 nm domain period by employing deep-UV laser lithography, chemical patterning, and electric field poling. An atomic force microscope was used to characterize the periodic domain structure. The sample was used to demonstrate sixth and seventh order quasi-phase-matched backward second-harmonic generation.

  • 6.
    Canalias, Carlota
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Progress in Sub-Micrometer Periodicity of Quasi-Phase Matching Structures2009In: 2009 Conference on Lasers and Electro-Optics and 2009 Conference on Quantum Electronics and Laser Science Conference, CLEO/QELS 2009, IEEE , 2009, p. 906-907Conference paper (Refereed)
    Abstract [en]

    We report on the progress in fabrication of sub-micrometer ferroelectric domain gratings in KTiOPO4. Periods as short as 565 nm have been created in the bulk of the crystal by electric-filed poling.

  • 7. Chesini, G.
    et al.
    Cordeiro, C. M. B.
    De Matos, C. J. S.
    Fokine, Mikael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Carvalho, I. C. S.
    Knighf, J. C.
    All-fiber devices based on photonic crystal fibers with integrated electrodes2008In: AIP Conference Proceedings, 2008, p. 109-112Conference paper (Refereed)
    Abstract [en]

    A special kind of microstructured optical fiber was proposed and manufactured where, as well as the holey region (solid core and silica-air cladding), the fiber has also two large holes for electrode insertion. Bi-Sn and Au-Sn alloys were selectively inserted in those holes forming two parallel, continuous and homogeneous internal electrodes. We demonstrated the production of a monolithic device and its use to externally control some of the guidance properties (e.g. polarization) of the fiber.

  • 8. Chesini, Giancarlo
    et al.
    Cordeiro, Cristiano M. B.
    de Matos, Christiano J. S.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Carvalho, Isabel C. S.
    Knight, J. C.
    All-fiber devices based on photonic crystal fibers with integrated electrodes2009In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 3, p. 1660-1665Article in journal (Refereed)
    Abstract [en]

    A special kind of microstructured optical fiber is proposed and fabricated in which, in addition to the holey region (solid core and silica-air cladding), two large holes exist for electrode insertion. Either Bi-Sn or Au-Sn alloys were selectively inserted into the large holes forming two parallel, continuous and homogeneous internal electrodes. We demonstrate the production of a monolithic device and its use to externally control some of the guidance properties (e. g. polarization) of the fiber.

  • 9. Coucheron, David A.
    et al.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Patil, Nilesh
    Breiby, Dag Werner
    Buset, Ole Tore
    Healy, Noel
    Peacock, Anna C.
    Hawkins, Thomas
    Jones, Max
    Ballato, John
    Gibson, Ursula J.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres2016In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 13265Article in journal (Refereed)
    Abstract [en]

    Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core.

  • 10. de Oliveira, R.
    et al.
    Sjödin, N.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Margulis, Walter
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    de Matos, C.
    Norin, L.
    Fabrication and Optical Characterization of Silica Optical Fibers Containing Gold Nanoparticles2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 1, p. 370-375Article in journal (Refereed)
    Abstract [en]

    Gold nanoparticles have been used since antiquity for the production of red-colored glasses. More recently, it was determined that this color is caused by plasmon resonance, which additionally increases the material's nonlinear optical response, allowing for the improvement of numerous optical devices. Interest in silica fibers containing gold nanoparticles has increased recently, aiming at the integration of nonlinear devices with conventional optical fibers. However, fabrication is challenging due to the high temperatures required for silica processing and fibers with gold nanoparticles were solely demonstrated using sol-gel techniques. We show a new fabrication technique based on standard preform/fiber fabrication methods, where nanoparticles are nucleated by heat in a furnace or by laser exposure with unprecedented control over particle size, concentration, and distribution. Plasmon absorption peaks exceeding 800 dB m(-1) at 514-536 nm wavelengths were observed, indicating higher achievable nanoparticle concentrations than previously reported. The measured resonant nonlinear refractive index, (6.75 ± 0.55) × 10(-15) m(2) W(-1), represents an improvement of >50×.

  • 11. dos Santos, F. Eroni P.
    et al.
    Favero, F. C.
    Gomes, A. S. L.
    Xing, J.
    Chen, Q.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Carvalho, I. C. S.
    Evaluation of the third-order nonlinear optical properties of tellurite glasses by thermally managed eclipse Z-scan2009In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 2Article in journal (Refereed)
    Abstract [en]

    The third-order nonlinearity is measured for TeO2-ZnO-Na2O (TZN) glasses codoped with BaO, Nb2O5, and La2O3. The results for the sign and magnitude of the nonlinearity were obtained using a combination of the eclipse Z-scan with thermal nonlinearity managed Z-scan, whereas the Kerr shutter technique was employed to obtain the electronic time response of the nonlinearity, all performed with 76 MHz repetition rate 150 fs pulses at 800 nm. The results show a fast response (< 200 fs) and a nonlinear refractive index varying from 1.5 to 3.5x10(-15) cm(2)/W, depending upon glass composition. At the peak power level employed, nonlinear absorption was negligible. The results obtained are in good agreement with other tellurite compositions reported, confirming the electronic origin of the nonlinearity.

  • 12. Fernandez, A. F.
    et al.
    Brichard, B.
    Berghmans, F.
    El Rabii, H.
    Fokine, Michael
    Popov, M.
    Chemical composition fiber gratings in a high mixed gamma neutron radiation field2006In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 53, no 3, p. 1607-1613Article in journal (Refereed)
    Abstract [en]

    Fiber Bragg gratings are all-fiber wavelength-selective refractive index structures manufactured through UV exposure of optical fibers. Their applications range from WDM all-fiber filters, dispersion compensators and fiber laser resonators for optical telecommunication applications to different types of point or distributed optical fiber sensors for a large variety of applications. The nuclear industry is considering the use of photonic technology for data communication in the next generation of nuclear power plants. In addition, fiber Bragg grating sensors are being evaluated by the nuclear industry for structural integrity and temperature monitoring. This work aims to study, in harsh radiation environments, a new type of FBG referred to as chemical composition grating. These gratings differ from other types of FBG in that their refractive index structure is attributed to a change in the chemical composition. Chemical composition gratings have shown to be extremely temperature stable surviving temperatures in excess of 1000 degrees C. We have experimentally studied the effect of very harsh gammaneutron radiation on the properties of chemical composition gratings fabricated in a Ge-F doped silica optical fiber.

  • 13.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Formation of thermally stable chemical composition gratings in optical fibers2002In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 19, no 8, p. 1759-1765Article in journal (Refereed)
    Abstract [en]

    Experimental results and a discussion of possible chemical pathways in the formation of thermally stable chemical composition gratings in optical fibers are presented. Gratings are formed through high-temperature treatment of UV-exposed hydrogen-loaded fibers. The final refractive-index modulation is ascribed to variations in fluorine concentration attained by periodically increased diffusion of fluorine. The mechanism behind this increase is the formation of mobile hydrogen fluoride from chemical reactions of fluorine and UV-induced hydroxyl, which occur with the spatial periodicity of the UV pattern. A hydroxyl-assisted increase in fluorine diffusion has been verified by time-of-flight secondary-ion mass spectroscopy. Formation of ultrastable grating by periodic variation of oxygen concentration through diffusion of molecular water is also discussed.

  • 14.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Growth dynamics of chemical composition gratings in flourine-doped silica optical fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, p. 1974-1976Article in journal (Refereed)
    Abstract [en]

    The refractive-index modulation of chemical composition gratings in fluorine-germanium-doped silica fibers as a function of thermal treatment during manufacturing has been studied. The final grating strength was found to depend strongly on an intermediate annealing step, with an optimum temperature near 600-700 degrees C, before development at a fixed temperature of 1000 degrees C. Low-temperature treatment, aimed at removing any remaining hydrogen from the fiber, performed at 100 degrees C for 20 h before the annealing step, also significantly increased the final refractive-index modulation.

  • 15. Fokine, Michael
    Growth dynamics of chemical composition gratings in fluorine-doped silica optical fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 22, p. 1974-1976Article in journal (Refereed)
    Abstract [en]

    The refractive-index modulation of chemical composition gratings in fluorine-germanium-doped silica fibers as a function of thermal treatment during manufacturing has been studied, The final grating strength was found to depend strongly on an intermediate annealing step, with an optimum temperature near 600-700degreesC before development at a fixed temperature of 1000degreesC. Low-temperature treatment, aimed at removing any remaining hydrogen from the fiber, performed at 100degreesC for 20 h before the annealing step, also sigificantly increased the final refractive-index modulation.

  • 16.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    High temperature miniature oven with low thermal gradient for processing fiber Bragg gratings2001In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 72, no 8, p. 3458-3461Article in journal (Refereed)
    Abstract [en]

    A miniature oven for processing fiber Bragg gratings in excess of 1000 degreesC has been projected and evaluated. The dimensions and the design of the oven allow rapid insertion and removal of the fiber during heating and minimizes mechanical degradation of the fiber. The 22 mm long oven has a flat zone at 1000 degreesC of 16 mm with a temperature variation of less than 2% and 20 mm with a temperature variation of 10%. The long term stability (hours) is +/- 20 degreesC measured at the center of the oven at 1000 degreesC. Rapid heating is possible, and heating optical fibers to 1000 degreesC shows a delay of approximately 400 ms before the core reaches thermal equilibrium.

  • 17.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Manipulating glass for photonics2009In: PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, ISSN 1862-6300, Vol. 206, no 5, p. 880-884Article in journal (Refereed)
    Abstract [en]

    A generalized concept for local manipulation of three-dimensional glass materials is described. The basic principle is to use means to deposit energy into the material to enable localized and selective changes in the bond structure of the glass matrix, causing a localized modification of the thermal equilibrium properties of the material. The different regions of the glass will then behave differently when the sample is subsequently heated homogeneously. If the difference in the thermal dynamics between modified and un-modified regions is significant, thermal treatment of the material can result in a self-organizing structure. The aim here is to provide a generalized concept of differential systems and self-organizing structures, using chemical composition Bragg gratings as an example. In this case, differential diffusion results in self-organizing structures consisting of a variation of the chemical composition, with compositional features smaller than 250 nm.

  • 18.
    Fokine, Michael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Photosensitivity, chemical composition gratings and optical fiber based components2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The different topics of this thesis include high-temperaturestable fiber Bragg gratings, photosensitivity and fiber basedcomponents.

    Fiber Bragg gratings (FBG) are wavelength dispersiverefractive index structures manufactured through UV exposure ofoptical fibers. Their applications range from WDM filters,dispersion compensators and fiber laser resonators fortelecommunication applications to different types of point ordistributed sensors for a variety of applications.

    One aim of this thesis has been to study a new type of FBGreferred to as chemical composition grating. These gratingsdiffer from other types of FBG in that their refractive indexstructure is attributed to a change in the chemicalcomposition. Chemical composition gratings have shown to beextremely temperature stable surviving temperatures in excessof 1000 oC. Photosensitivity of pure silica and germanium-dopedcore fibers in the presence of hydroxyl groups has also beenstudied and different types of fiber based components have beendeveloped.

    The main result of the thesis is a better understanding ofthe underlying mechanism of the formation of chemicalcomposition gratings and their decay behavior at elevatedtemperatures. The refractive index modulation is caused by aperiodic change in the fluorine concentration, which has beenverified through time-of-flight secondary-ion-mass spectrometryand through studies of the decay behavior of chemicalcomposition gratings. A model based on diffusion of dopants hasbeen developed, which successfully predicts the thermal decayat elevated temperatures. Studies of the dynamics of chemicalcomposition grating formation have resulted in a manufacturingtechnique that allows for reproducible gratingfabrication.

    The main results regarding photosensitivity is a method tosignificantly increase the effect of UV radiation on standardtelecommunications fiber. The method, referred to asOH-flooding, has also been applied to pure-silica core fibersresulting in the first report of strong grating formation insuch fibers.

    Finally, research into different schemes for developingfiber-based components has resulted in two types of singlefiber integrated Mach-Zehnder interferometers; one passiveinterferometer that can be used as an optical filter and oneactive interferometer controlled with internal metalelectrodes.

    Keywords:optical fibers, fiber Bragg gratings,photosensitivity, thermal stability, fiber sensors, chemicalcomposition gratings, fiber components, Mach-Zehnderinterferometer, optical switch, optical modulator.

  • 19.
    Fokine, Michael
    KTH, Superseded Departments, Physics.
    Thermal stability of chemical composition gratings in fluorine-germanium-doped silica fibers2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 12, p. 1016-1018Article in journal (Refereed)
    Abstract [en]

    A model based on diffusion of dopants in a periodic structure has been applied to describe thermal decay of chemical composition gratings in fluorine-germanium-doped silica fibers. The good agreement between previously reported values and the diffusion coefficients derived here from experiments and models in the 1000 - 1200 degreesC temperature range indicate that fluorine diffusion is the main mechanism of grating decay. Experimental results also indicate that the presence of phosphorous significantly increases the decay rate of chemical composition gratings.

  • 20. Fokine, Michael
    Thermal stability of oxygen-modulated chemical-composition gratings in standard telecommunication fiber2004In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 29, no 11, p. 1185-1187Article in journal (Refereed)
    Abstract [en]

    Experimental results and a discussion on the formation and decay of oxygen-modulated chemical-composition gratings in a standard telecommunication fiber are presented. Comparison between the decay experiment and the model provides a diffusion coefficient with an activation energy of 490 kJ/mol, which is in close agreement with reported values of oxygen self-diffusion in silica. The gratings have a diffusion-controlled decay behavior, with more than 50% of the reflectivity remaining after 7.5 h at a temperature of 1230degreesC. The gratings show higher thermal stability when heated in air than in an inert argon atmosphere.

  • 21. Fokine, Michael
    Underlying mechanisms, applications, and limitations of chemical composition gratings in silica based fibers2004In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 349, p. 98-104Article in journal (Refereed)
    Abstract [en]

    This paper reviews the manufacturing procedure and properties of high-temperature stable chemical composition gratings in silica based optical fibers. Chemical composition gratings are formed by a periodic change in the distribution of dopants by UV exposure and thermal processing, which results in differential diffusion. This is attained through interaction between dopants in the fiber and UV induced hydroxyl groups. The formation of fluorine and oxygen modulated chemical composition gratings is presented and their applications and limitations are discussed.

  • 22.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    What is the limit of thermal stability for short-period fiber Bragg gratings?2011Conference paper (Other academic)
  • 23.
    Fokine, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Chen, Yiting
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Wang, Jing
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Hao, Jiaming
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Meiser, Niels
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Optical Characterization of Plasmonic Metamaterial Absorber2010Conference paper (Refereed)
    Abstract [en]

    A reflectance/transmittance experiment setup to characterize a sub-wavelength, wide-angle, ultrathin metamaterial absorber at optical frequency regime is shown, and the measured results are presented.

  • 24.
    Fokine, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Hoon, Jang
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    M. P. Goueva, Paula
    Pontifícia Universidade Católica do Rio de Janeiro.
    M. B. Braga, Arthur
    Pontifícia Universidade Católica do Rio de Janeiro.
    C. S. Carvalho, Isabel
    Pontifícia Universidade Católica do Rio de Janeiro.
    Spectral features of specular reflection from nanoparticle films2010In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 8, no 9, p. 2673-2675Article in journal (Refereed)
    Abstract [en]

    In this work we analyze the internal reflection (Fresnel reflection) from Au nanoparticles on the end face of optical fibers. We demonstrate that changes in the refractive index of the surrounding medium can be detected by shifts in the reflection spectra associated with changes in the Localized Surface Plasmon Resonance of the Au-Nanoparticles. The spectral response is simulated using a model based on the interference in multilayer structures and can be described by transfer-matrix method.

  • 25.
    Fokine, Michael
    et al.
    KTH, Superseded Departments, Physics.
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Large increase in photosensitivity through massive hydroxyl formation2000In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 25, no 5, p. 302-304Article in journal (Refereed)
    Abstract [en]

    We report a large increase in photosensitivity of germanium-doped silicate fibers by rapid heat treatment of hydrogen-loaded fibers at 1000 degrees C before exposure of the fibers to 242-nm radiation. The increase in photosensitivity is compared with thermally induced absorption caused by introduction of massive amounts of hydroxyl species. The absorption loss was measured to be 0.02 dB/cm mol.% OH at 1.55 mu m. Strong gratings (Delta n > 1 x 10(-4)) in germanium-free phosphorous-doped fibers in the presence of 242-nm radiation have also been manufactured by this technique.

  • 26.
    Fokine, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Moreira, Fabio D.
    Carvalho, Isabel C. S.
    Poled glasses for optical devices2008In: Photonics North 2008 / [ed] Vallee, R; Piche, M, 2008, Vol. 7099, p. 709918-Conference paper (Refereed)
    Abstract [en]

    Thermal poling is an efficient way to induce optical second-order nonlinearity in different types of glasses, which typically have macroscopic inversion symmetry. In this paper we present a study on the current dynamics during thermal poling of glasses and relate these results to the formation dynamics of the depletion region, which is closely linked to the induced optical second order nonlinearity. Based on a simple theoretical viewpoint, supported by experimental results, we propose that thermal poling of glasses, and space-charge formation in dielectrics in general, can be viewed as an ionic RC circuit. This, to some extent modified view oil thermal poling in glasses, opens up new opportunities to study and control the depletion layer dynamics subsequently leading to better control of the thermal poling induced optical second order nonlinearity in glasses.

  • 27. Fokine, Michael
    et al.
    Saito, K.
    Ikushima, A. J.
    Thermally induced second-order nonlinearity in silica-based glasses2005In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 87, no 17Article in journal (Refereed)
    Abstract [en]

    This letter presents the observation of second-harmonic generation in pure silica and germanium-doped glass samples after heat treatment at elevated temperatures followed by rapid quenching to room temperature. No applied voltage has been used and the samples do not contain crystals. The induced nonlinearity is located near the surfaces of the sample. The possible origin of the second-order nonlinearity is discussed.

  • 28. Fokine, Michael
    et al.
    Suzuki, H.
    Goto, T.
    Salto, K.
    Ikushima, A. J.
    High-temperature treatment of hydrogen loaded GeO2: SiO2 glasses for photonic device fabrication2006In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 352, no 07-jun, p. 494-499Article in journal (Refereed)
    Abstract [en]

    High-temperature treatment of hydrogen loaded silica- and germanium doped silica glass, also referred to as OH flooding, has been studied. The removal mechanism of hydroxyl groups in silica glass, during OH flooding, occurs by formation and diffusion of molecular hydrogen, while in germanium doped silica the main diffusion mechanism is attributed to diffusion of molecular water. UV exposure of OH flooded and non-treated germanium doped silica samples, from a ArF laser at 193 nm, show large changes in the asymmetric stretching vibration of Si-O-Si bridges, indicating compaction of the glass network. In addition, the thermal relaxation kinetics of the UV induced compaction are found to be similar for non-treated samples and OH flooded samples.

  • 29.
    Fokine, Michael
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Theodosiou, Antreas
    Song, Seunghan
    Hawkins, Thomas
    Ballato, John
    Kalli, Kyriacos
    Gibson, Ursula J.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Laser structuring, stress modification and Bragg grating inscription in silicon-core glass fibers2017In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 7, no 5, p. 1589-1597Article in journal (Refereed)
    Abstract [en]

    Semiconductor core fibers have numerous potential applications in optoelectronics and photonics, and the key to realizing these opportunities is controlled processing of the material. We present results on laser treatments for manipulating the core structure as well as the glass cladding. More specifically, using quasi-CW 10.6 mu m radiation, the clad glass can be softened and the core can be controllably melted. This is shown to permit tapering, localized formation of optical resonators, and stress modification of the as-drawn fiber and structures within it. Shown for the first time to the authors' knowledge are Bragg gratings written by modification of the silicon/glass interface using fs laser illumination at 517 nm. The cores of these fibers show stress alterations, with indications of quasi-periodic stress relief in the glass.

  • 30.
    Fokine, Mikael
    et al.
    KTH, Superseded Departments, Physics.
    Nilsson, Lars-Erik
    Claesson, Åke
    Berlemont, D
    Kjellberg, L
    Krummenacher, L
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Integrated fiber Mach-Zehnder interferometer for electro-optic switching2002In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 27, no 18, p. 1643-1645Article in journal (Refereed)
    Abstract [en]

    Molten alloys under high pressure were used to obtain fibers with long internal electrodes that are solid at room temperature. An integrated Mach-Zehnder interferometer was constructed from a twin-core twin-hole fiber that permitted application of an electric field preferentially to one of the cores. Good stability and a switching voltage of 1.4 kV were measured with a 1-m-long fiber device with a quadratic voltage dependence.

  • 31. Garcia, FC
    et al.
    Fokine, Mikael
    KTH, Superseded Departments, Physics.
    Margulis, Walter
    KTH, Superseded Departments, Physics.
    Kashyap, Raman
    Mach-Zehnder interferometer using single standard telecommunication optical fibre2001In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 37, no 24, p. 1440-1442Article in journal (Refereed)
    Abstract [en]

    It is demonstrated that a single, short-length, standard telecommunications optical fibre can function as an interferometer when subjected to hydroxyl-flooding. The interferometer is based on the mode beating effect arising from the induced-refractive index change.

  • 32.
    Gibson, Ursula J.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Ballato, J.
    United States.
    Peacock, A.
    United Kingdom.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Engineering Sciences (SCI), Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics. KTH, School of Engineering Sciences (SCI), Physics.
    Future of semiconductor-core optical fibers2018In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018Conference paper (Refereed)
    Abstract [en]

    Semiconductor-core optical fibers hold promise for long wavelength transmission systems as well as for nonlinear and active optoelectronic devices. This talk includes a status report on fiber properties and a prospectus of some future directions.

  • 33.
    Gibson, Ursula J.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Healy, N.
    Song, S.
    Svendson, S.
    Osterberg, U.
    Peacock, A. C.
    Ballato, J.
    Semiconductor core fibers for optoelectronics2017In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2017Conference paper (Refereed)
  • 34. Gouvea, Paula M. P.
    et al.
    Jang, Hoon
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Carvalho, Isabel C. S.
    Cremona, M.
    Braga, Arthur M. B.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Internal specular reflection from nanoparticle layers on the end face of optical fibers2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 10, p. 103114-Article in journal (Refereed)
    Abstract [en]

    Metal nanoparticles deposited on a dielectric substrate exhibit an absorption peak due to localized surface plasmon resonance (LSPR). Changes in the refractive index of the surrounding medium cause the LSPR band to shift in wavelength. In this paper, gold nanoparticles were placed on the end face of an optical fiber spliced to a reflection setup. As expected in reflection geometries, the back-reflected signal exhibits a dip at wavelengths in the LSPR band when the fiber tip is surrounded by ambient air (n = 1). However, as the refractive index of the surrounding medium is increased, there is a gradual inversion from a dip (n = 1.0) to a peak (n = 2.0). To explain these results, a model based on absorption and interference between the specular reflections from the fiber/nanoparticle and nanoparticle/ambient interfaces is proposed, showing that our reflection configuration can be used in sensing applications.

  • 35. Gouvêa, P. M. P.
    et al.
    Carvalho, I. C. S.
    Jang, Hoon
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Cremona, M.
    Braga, A. M. B.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Characterization of a fiber optic sensor based on LSPR and specular reflection2010In: Optical Sensors (Sensors) 2010, 2010Conference paper (Refereed)
    Abstract [en]

    A fiber optic sensor based on Localized Surface Plasmon Resonance (LSPR) and specular reflection has been characterized as a function of refractive índex. The sensitivity has been obtained for the range from n=1.0 to n=2.0.

  • 36.
    Guo, Wenhua
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Holmberg, Patrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fabrication of long-period fiber gratings through periodic ablation using a focused CO2-laser beam2015In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 5, no 11, p. 2702-2714Article in journal (Refereed)
    Abstract [en]

    Fabrication of long period gratings in optical fibers through periodic ablation using a focused CO2 laser beam has been studied. During the thermal ablation process most of the energy is absorbed at the glass surface, due to the high extinction coefficient of silica at the laser wavelength, resulting in rapid increase in temperature. Subsequent heat dissipation occurs through vaporization and ejection of molten material, heat conduction axially along the fiber, radiation and through convection. The high surface temperatures involved during ablation can result in a significant increase in temperature of the fiber itself, causing unwanted off-resonance background losses during grating fabrication. In order to minimize losses the temperature needs to be sufficiently low to avoid micro-bending and core deformation, triggered by the decrease in viscosity, while at the same time enabling strong grating formation through laser induced modification of the glass. In this work we have used short-period fiber Bragg gratings in order to assess the temperature dynamics within the fiber during ablation. Using a single grating written into the core, positioned below the point of ablation, we measure the peak temperature within the core of the fiber. When ablation was performed between two gratings, forming a short Fabry-Perot cavity, a different and faster response was recorded, which we ascribe to thermally induced stress and strain caused by the thermal expansion of the surface during ablation. By identifying suitable processing parameters we successfully fabricate strong long-period gratings with background losses of 0.5 dB to 1 dB when periodically ablating the fiber with up to 50 pulses. Experimental results indicate that the maximum core temperatures during ablation under these conditions are limited to within 600 degrees C to 1000 degrees C.

  • 37. Healy, N.
    et al.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Franz, Y.
    Hawkins, T.
    Jones, M.
    Ballato, J.
    Peacock, A. C.
    Gibson, U. J.
    CO2 Laser-Induced Directional Recrystallization to Produce Single Crystal Silicon-Core Optical Fibers with Low Loss2016In: Advanced Optical Materials, ISSN 2195-1071Article in journal (Refereed)
  • 38. Hellsing, M
    et al.
    Fokine, Michael
    Claesson, A
    Nilsson, E
    Margulis, Walter
    ToF-SIMS imaging of dopant diffusion in optical fibers2003In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 203, p. 648-651Article in journal (Refereed)
    Abstract [en]

    Applications of optical fibers in telecommunication and sensing are rapidly emerging where the fiber properties are related to the controlled addition of dopants such as germanium, phosphorous, fluorine and erbium. The modern ToF-SIMS instrument, with its high sensitivity and high lateral resolution, has shown to be an excellent tool to directly analyze cross-sections of as-manufactured fibers. The present work describes ToF-SIMS imaging of the dopant distribution in fluorine, germanium and rare-earth doped fibers where dopants are confined to a few mum in the core. The increased fluorine diffusion in the fluorine doped fibers due to chemical reactions with hydroxyl groups was examined. This process is utilized in the manufacture of thermally stable chemical composition fiber Bragg gratings. We were able to produce ToF-SIMS elemental images with a lateral resolution around 0.5 mum showing the detailed distribution of the dopants.

  • 39. Hirose, T.
    et al.
    Fokine, Michael
    Saito, K.
    Ikushima, A. J.
    Waveguide writing by CO2 laser annealing on sputtered silica film2006In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 352, no 07-jun, p. 664-668Article in journal (Refereed)
    Abstract [en]

    We present a novel method for creating refractive-index structures in sputtered silica film using CO2 laser annealing. The silica film was prepared by radio frequency magnetron sputtering on silica substrate. Deposited film with the refractive-index 0.8% higher than that of the silica substrate was realized, with a propagation loss of 0.4 dB/cm. The refractive-index of the silica film could be reduced by CO2 laser annealing, enabling the formation of cladding structure for 2-D waveguide.

  • 40.
    Holmberg, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Chemical composition gratings2014In: Specialty Optical Fibers, SOF 2014, Optical Society of America, 2014Conference paper (Refereed)
    Abstract [en]

    High-temperature stable fiber Bragg gratings will be reviewed with an emphasis on recent material studies using Chemical Composition gratings.

  • 41.
    Holmberg, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Monitoring temperature in optical fibers during thermal processing2013In: Optics InfoBase Conference Papers, 2013Conference paper (Refereed)
    Abstract [en]

    Temperature dynamics in optical fibers during CO2-laser irradiation, at temperatures above the softening point of fused silica, were characterized using chemical composition gratings. The technique offers possibilities for enhanced temperature control during optical fiber processing.

  • 42.
    Holmberg, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Thermometric study of CO2-laser heated optical fibers in excess of 1700 degrees C using fiber Bragg gratings2013In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 30, no 7, p. 1835-1842Article in journal (Refereed)
    Abstract [en]

    The thermal response of optical fibers during CO2 laser irradiation has been characterized by using thermally stable short-period fiber Bragg gratings, referred to as chemical composition gratings. CO2 laser beam profiling was performed by scanning the beam across a 1 mm long grating, providing a spatial resolution given by the fiber diameter. The thermal dynamics during square pulse irradiation has been recorded for temperatures in excess of 1700°C, with heating and cooling rates as high as 10,500°C  s−1 and 6500°C  s−1, respectively.

  • 43.
    Holmberg, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Using Fiber Bragg Gratings to measure temperatures up to 2000 K2012Conference paper (Other academic)
    Abstract [en]

    The thermal response of optical fibers during CO2 laser irradiation with a wavelength of 10.6 µm has been characterized by use of thermally stable short period fiber Bragg gratings, referred to as chemical composition gratings.Beam profiling of the collimated beam from a CO2laser having a 1/e2 diameter of ~6.5 mm, was performed with a spatial resolution given by the fiber diameter. Heating- and cooling-dynamics of the fiber irradiated with a square pulse with a 1/e rise time of < 1 ms were performed with a temporal resolution down to~250 µs, for temperatures in excess of 1700 ºC.

  • 44.
    Holmberg, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Influence of pre-annealing on the thermal regeneration of fiber Bragg gratings in standard optical fibers2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 21, p. 27520-27535Article in journal (Refereed)
    Abstract [en]

    A detailed study of the dynamics during thermal regeneration of fiber Bragg gratings, written in hydrogen-loaded standard single-mode fibers using a ns pulsed 213 nm UV laser, is reported. Isothermal pre-annealing performed in the range 85 degrees C to 1100 degrees C, with subsequent grating regeneration at 1100 degrees C, resulted in a maximum refractive index modulation, Delta n(m) similar to 1.4.10(-4), for gratings pre-annealed near 900 degrees C while a minimum value of Delta n(m) similar to 2.10(-5) was achieved irrespective of pre-annealing temperature. This optimum denote an inflection point between opposing thermally triggered processes, which we ascribe to the reaction-diffusion mechanism of molecular water and hydroxyl species in silica. The results shed new light on the mechanisms underlying thermal grating regeneration in optical fibers.

  • 45.
    Holmberg, Patrik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Pasiskevicius, Valdas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Study of incubation effects during surface ablation using picosecond pulses at a wavelength of 800 nm2011In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 8, no 9, p. 2862-2865Article in journal (Refereed)
    Abstract [en]

    A comparison of laser ablation on the front-surface (surface facing the laser) and back-surface of 1.1 mm thick boro-aluminosilicate glass plates has been performed using 1 ps pulses at a wavelength of 800 nm. The resulting structures of front- and back-surface ablation are compared relative to an input design geometry of 40 µm deep and 40 µm wide surface channels. The influence of incubation effects on the final structure is discussed.

  • 46.
    Liao, Guihua
    et al.
    Politecnico di Torino.
    Chen, Qiuping
    Politecnico di Torino.
    Xing, Jianjun
    Politecnico di Torino.
    Gebavi, Hrvoje
    Politecnico di Torino.
    Milanese, Daniel
    Politecnico di Torino.
    Fokine, Michael
    Politecnico di Torino.
    Ferraris, Monica
    Politecnico di Torino.
    Preparation and characterization of new fluorotellurite glasses for photonics application2009In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 355, no 7, p. 447-452Article in journal (Refereed)
    Abstract [en]

    Glasses based on (85 − x)TeO2xZnF2–12PbO–3Nb2O5 (x = 0–40) system have been studied for the first time for fabricating mid-infrared optical fiber lasers. The thermal and optical properties including UV–Vis, Raman as well as FTIR spectra are reported. It is demonstrated that increasing the ZnF2 concentration to 30 mol% significantly increased the thermal stability of the glass. Adding ZnF2 also reduced the hydroxyl (OH) content of the glass resulting in lower optical absorption in the mid-infrared region, which is crucial for infrared laser applications. The glass absorption cut-off edge near 400 nm blue-shifts with increasing ZnF2 addition. Raman spectra show a depolymerization of the glass network with increasing transformation of TeO3+1 to TeO3 structures.

  • 47.
    Liu, Chunxin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Yang, Xiong
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Laurell, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fokine, Michael
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Fabrication of a widely tunable fiber Bragg grating filter using fused deposition modeling 3D printing2019In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 9, no 11, p. 4409-Article in journal (Refereed)
    Abstract [en]

    The use of 3D-printing for designing a simple wavelength tunable device based on fiber Bragg gratings is demonstrated. Using fused deposition modeling (FDM), the fiber Bragg grating is embedded into a beam of polyethylene terephthalate glycol (PETG). Through bending, resulting in compression or tension of the optical fiber, the Bragg wavelength could be continuously tuned over a range of 60 nm, with maintained reflectivity and 3-dB linewidth.

  • 48. Maciel, Glauco S.
    et al.
    Rakov, Nikifor
    Fokine, Michael
    Carvalho, Isabel C. S.
    Pinheiro, Carlos B.
    Strong upconversion from Er3Al5O12 ceramic powders prepared by low temperature direct combustion synthesis2006In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 89, no 8Article in journal (Refereed)
    Abstract [en]

    Crystalline ceramic powders of Er3Al5O12 were obtained by low temperature direct combustion synthesis. Irradiating the sample with a low-power continuous-wave infrared (1.48 mu m) diode laser led to ultraviolet, violet, blue, green, and red (380, 410, 456, 495, 525, 550, and 660 nm) emissions. The strong upconversion luminescence appeared to the eyes as an intense green color. The presence of efficient four- and three-photon frequency upconversion processes makes this material an excellent candidate for use in photonic devices based on upconverter phosphors.

  • 49.
    Myrén, Niklas
    et al.
    KTH, Superseded Departments, Physics.
    Fokine, Michael
    Kjellberg, Leif
    Helander, Per
    Norin, Lars
    Olsson, Håkan
    Sjödin, Niclas
    Margulius, Walter
    A Fibre-Based Kerr Switch and Modulator2004In: 30th Eruopean Conference on Optical Communications: Stockholm, Sweden. Sept 2004, 2004Conference paper (Refereed)
  • 50. Pal, S.
    et al.
    Mandal, J.
    Sun, T.
    Grattan, K. T. V.
    Fokine, Michael
    Carlsson, F.
    Fonjallaz, P. Y.
    Wade, S. A.
    Collins, S. F.
    Characteristics of potential fibre Bragg grating sensor-based devices at elevated temperatures2003In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 14, no 7, p. 1131-1136Article in journal (Refereed)
    Abstract [en]

    Fibre Bragg gratings (FBGs) of type I and IIA were fabricated in Ge-doped and B-Ge co-doped fibres using a 248 nm excimer laser and their performance characteristics were tested and compared with those of a chemical composition grating (CCG), written in a fluorine-germanium doped fibre, over a wide range of temperatures. Long-term testing (more than 600 h) involving a series of step-wise incremental temperature changes shows for the first time the potential of FBGs for high temperature measurement applications (up to and beyond 1100 degreesC), this depending on the type of FBG involved and the material and composition of the substrate fibre (the CCG was observed to be the most durable at very high temperatures). These gratings are likely to be useful for the simultaneous measurement of strain and temperature over these higher temperature ranges.

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