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Träfflista för sökning "WFRF:(Ballato J.) "

Sökning: WFRF:(Ballato J.)

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1.
  • Aktas, Ozan, et al. (författare)
  • Interfacing telecom fibers and silicon core fibers with nano-spikes for in-fiber silicon devices
  • 2018
  • Ingår i: 2018 Optical Fiber Communications Conference and Exposition, OFC 2018 - Proceedings. - : Institute of Electrical and Electronics Engineers Inc. (IEEE). ; , s. 1-3
  • Konferensbidrag (refereegranskat)abstract
    • We report fabrication of tapered silicon core fibers with nano-spikes enabling efficient optical coupling into the core, as well as their seamless integration with single mode fibers. A proof-of-concept integrated in-fiber silicon device is demonstrated.
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2.
  • Frey, B. N., et al. (författare)
  • Cooling Yb-Doped Silica Fibers and Fiber Lasers with Anti-Stokes Pumping
  • 2023
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510659797
  • Konferensbidrag (refereegranskat)abstract
    • Optical cooling in Yb-doped silica fibers using anti-Stokes fluorescence has become a subject of great interest in the fiber laser community. This paper provides an update on the development of silica fibers designed specifically to enhance their cooling properties. This growing list includes a new, nearly single-mode fiber with a borophosphosilicate core that produced –65 mK of cooling with only 260 mW of 1040-nm pump power. The silica compositions that have now been successfully cooled at atmospheric pressure by anti-Stokes fluorescence by our team include aluminosilicate, aluminofluorosilicate, borophosphosilicate, and aluminosilicate doped with one of three different alkali-earth nanoparticles (Ba, Sr, and Ca). By fitting the measured temperature dependence of the cooled fiber on pump power, two key parameters that control the degree of cooling are inferred, namely the critical quenching concentration and the absorptive loss due to impurities. The inferred values compiled for the fibers that cooled indicate that the extracted heat is highest when the Yb concentration is 2 wt.% or more (to maximize heat extraction), the Al concentration is ~0.8 wt.% or greater (to reduce quenching), and the absorptive loss is below approximately 15 dB/km, and ideally below 5 dB/km (to minimize heating due to pump absorption). Only two of the reported fibers, an LaF3-doped and an LuF3-doped nanoparticle fiber, did not cool, because their Yb and Al concentrations were not sufficiently high. This analysis shows that through careful composition control (especially the Al and Yb concentrations) and minimization of the OH contamination, a new generation of Yb-doped silica fibers is emerging with higher Yb concentrations, greater resistance to quenching, and lower residual loss than commercial Yb-doped fibers. They can be expected to have a significant impact not only on optically cooled devices but also on a much broader range of fiber lasers and amplifiers. 
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3.
  • Knall, J., et al. (författare)
  • Radiation-balanced silica fiber laser
  • 2021
  • Ingår i: Optica. - 2334-2536. ; 8:6, s. 830-833
  • Tidskriftsartikel (refereegranskat)abstract
    • In optically pumped lasers, heat generated by the quantum defect causes detrimental fluctuations in the output mode, frequency, and power. Common heat-mitigation techniques use bulky mechanical coolers that introduce vibrations, leading to laser frequency and amplitude noise. Here, we present a radiation-balanced fiber laser, optically cooled by anti-Stokes fluorescence (ASF). The gain medium is a silica fiber with a 21-µm-diameter core doped with 2.06 wt. % Yb3+ and co-doped with Al2O3 and F- to reduce concentration quenching. The laser was core-pumped at 1040 nm to create both gain at 1065 nm and ASF cooling at atmospheric pressure. We demonstrate a maximum output power of 114 mW with a slope efficiency of 41% while maintaining near-zero average temperature change. This result could enable the development of fiber lasers with unprecedented coherence and stability. 
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4.
  • Ren, H., et al. (författare)
  • Low-loss silicon core fibre platform for mid-infrared nonlinear photonics
  • 2019
  • Ingår i: Light. - : Springer Nature. - 2095-5545 .- 2047-7538. ; 8:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Broadband mid-infrared light sources are highly desired for wide-ranging applications that span free-space communications to spectroscopy. In recent years, silicon has attracted great interest as a platform for nonlinear optical wavelength conversion in this region, owing to its low losses (linear and nonlinear) and high stability. However, most research in this area has made use of small core waveguides fabricated from silicon-on-insulator platforms, which suffer from high absorption losses of the use of silica cladding, limiting their ability to generate light beyond 3 µm. Here, we design and demonstrate a compact silicon core, silica-clad waveguide platform that has low losses across the entire silicon transparency window. The waveguides are fabricated from a silicon core fibre that is tapered to engineer mode properties to ensure efficient nonlinear propagation in the core with minimal interaction of the mid-infrared light with the cladding. These waveguides exhibit many of the benefits of fibre platforms, such as a high coupling efficiency and power handling capability, allowing for the generation of mid-infrared supercontinuum spectra with high brightness and coherence spanning almost two octaves (1.6–5.3 µm).
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5.
  • Song, S., et al. (författare)
  • Crystalline GaSb-core optical fibers with room-temperature photoluminescence
  • 2018
  • Ingår i: Optical Materials Express. - : OPTICAL SOC AMER. - 2159-3930 .- 2159-3930. ; 8:6, s. 1435-1440
  • Tidskriftsartikel (refereegranskat)abstract
    • Glass-clad, GaSb-core fibers were drawn and subsequently laser annealed. The as-drawn fibers were found to be polycrystalline, possess Sb inclusions, and have oxide contamination concentrations of less than 3 at%. Melting and resolidifying regions in the cores using 10.6 mu m CO2 laser radiation yielded single crystalline zones with enhanced photoluminescence (PL), including the first observation of strong room temperature PL from a crystalline core fiber. Annealed fibers show low values of tensile strain and a bandgap close to that of bulk GaSb. 
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6.
  • Ballato, J., et al. (författare)
  • Material approaches to thermal management in advanced fiber lasers and amplifiers
  • 2023
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510659797
  • Konferensbidrag (refereegranskat)abstract
    • For as long as light and matter have partnered, impurities have played a role in optical system performance. This remains generally true for photonic heat engines and especially the case for optical refrigeration. Building on the history of light and glass, including the materials development of low loss telecom fibers, this paper briefly discusses the sources of heat generation in materials and all-material means for their reduction. Particularly attention will be paid to active optical fibers and connect thermal management to parasitic optical nonlinearities, both critical to high and low power amplifier and laser systems. 
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7.
  • Balliu, Enkeleda, PhD student, et al. (författare)
  • High-efficiency radiation-balanced Yb-doped silica fiber laser with 200-mW output
  • 2024
  • Ingår i: Optics Letters. - : Optica Publishing Group. - 0146-9592 .- 1539-4794. ; 49:8, s. 2021-2024
  • Tidskriftsartikel (refereegranskat)abstract
    • The focus of this study was the development of a second generation of fiber lasers internally cooled by anti-Stokes fluorescence. The laser consisted of a length of a single-mode fiber spliced to fiber Bragg gratings to form the optical resonator. The fiber was single-moded at the pump (1040 nm) and signal (1064 nm) wavelengths. Its core was heavily doped with Yb, in the initial form of CaF2 nanoparticles, and co-doped with Al to reduce quenching and improve the cooling efficiency. After optimizing the fiber length (4.1 m) and output-coupler reflectivity (3.3%), the fiber laser exhibited a threshold of 160 mW, an optical efficiency of 56.8%, and a radiation-balanced output power (no net heat generation) of 192 mW. On all three metrics, this performance is significantly better than the only previously reported radiation-balanced fiber laser, which is even more meaningful given that the small size of the single-mode fiber core (7.8-µm diameter). At the maximum output power (∼2 W), the average fiber temperature was still barely above room temperature (428 mK). This work demonstrates that with anti-Stokes pumping, it is possible to induce significant gain and energy storage in a small-core Yb-doped fiber while keeping the fiber cool. 
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8.
  • Balliu, Enkeleda, PhD student, et al. (författare)
  • Improved Closed-Loop Slow-Light Temperature Sensor With Millidegree Resolution for Laser Cooling
  • 2023
  • Ingår i: Proceedings - 28th International Conference on Optical Fiber Sensors, OFS 2023. - : Optica Publishing Group.
  • Konferensbidrag (refereegranskat)abstract
    • For applications such as laser cooling of doped fibers, where it is critical to measure accurately the temperature of a cooled fiber that is very close to room temperature, it is paramount to develop a reliable, very short (mm) fiber temperature sensor with millikelvin resolution and very little drift. We report a second generation of a unique slow-light fiber Bragg grating (FBG) temperature sensor that meets these stringent requirements. Experiments and modeling establish that its temperature response depends only on well-known material constants of the silica FBG and the response of the probe laser's wavelength controller. The response is independent of the linewidth of the slow-light resonance, hence different FBGs and/or resonances have the exact same response. Examples of measured cooling in optically pumped Yb-doped fibers show that more reliable thermal contact with the cooled fiber is obtained by wrapping the FBG and the cooled fiber. 
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9.
  • Gibson, Ursula J., et al. (författare)
  • Future of semiconductor-core optical fibers
  • 2018
  • Ingår i: Optics InfoBase Conference Papers. - : OSA - The Optical Society. - 9781557528209
  • Konferensbidrag (refereegranskat)abstract
    • 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.
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10.
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11.
  • Gibson, U. J., et al. (författare)
  • Semiconductor-core optical fibers
  • 2017
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. ; , s. 22-23
  • Konferensbidrag (refereegranskat)abstract
    • Recent results on silicon and SiGe-core fibers for infrared applications, as well as newdata on III-V core materials, and device concepts for semiconductor-core fibers are presented.
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12.
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13.
  • Knall, J. M., et al. (författare)
  • Experimental observation of cooling in Yb-doped silica fibers
  • 2020
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE - International Society for Optical Engineering. - 9781510633599
  • Konferensbidrag (refereegranskat)abstract
    • Anti-Stokes fluorescence cooling in a silica-based fiber is reported for the first time. The fiber had a core with a 20-μm diameter doped with 2.06 wt.% Yb and co-doped with 0.86 wt.% Al and 0.88 wt.% F. Core-pumping the fiber with 1040- nm light, temperature changes as large at -50 mK were measured at atmospheric pressure. Temperature measurements were performed at 12 pump wavelengths, and the measured dependence of the temperature change as a function of pump wavelength was in excellent agreement with a previously reported model. With this model, the absorptive loss in the fiber was inferred to be less than 15 dB/km, and the critical quenching concentration to be ∼15.6 wt.% Yb. This combination of low loss and high quenching concentration (a factor of 16 times higher than the highest reported values for Yb-doped silica) is what allowed the observation of cooling. The temperature measurements were performed at atmospheric pressure using a custom slow-light fiber Bragg grating sensor with an improved thermal contact between the test fiber and the FBG. The improved method involves isopropanol to establish a good thermal contact between the two fibers. This eliminated a source of heating and enabled more accurate measurements of the cooled-fiber temperature. This improved temperaturemeasurement set-up also led to a new cooling record in a multimode Yb-doped ZBLAN fiber at atmospheric pressure. When pumped at 1030 nm, the fiber cooled by -3.5 K, a factor of 5.4 times higher than the previous record. 
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14.
  • Ren, H., et al. (författare)
  • Nonlinear optical properties of polycrystalline silicon core fibers from telecom wavelengths into the mid-infrared spectral region
  • 2019
  • Ingår i: Optical Materials Express. - : OPTICAL SOC AMER. - 2159-3930 .- 2159-3930. ; 9:3, s. 1271-1279
  • Tidskriftsartikel (refereegranskat)abstract
    • Polycrystalline silicon core fibers (SCFs) fabricated via the molten core drawing (MCD) method are emerging as a flexible optoelectronic platform. Here, the optical transmission properties of MCD SCFs that have been tapered down to a few micrometer-sized core dimensions are characterized from the telecom band to the mid-infrared spectal regime. The SCFs exhibit low linear losses on the order of a few dB/cm over the entire wavelength range. Characterization of the two-photon absorption coefficient (beta(TPA)) and nonlinear refractive index (n(2)) of the SCFs reveals values consistent with previous measurements of single crystal silicon materials, indicating the high optical quality of the polysilicon core material. The high nonlinear figure of merit obtained for wavelengths above 2 mu m highlight the potential for these fibers to find application in infrared nonlinear photonics. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.
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15.
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16.
  • Song, S., et al. (författare)
  • Laser restructuring and photoluminescence of glass-clad GaSb/Si-core optical fibres
  • 2019
  • Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
  • Tidskriftsartikel (refereegranskat)abstract
    • Semiconductor-core optical fibres have potential applications in photonics and optoelectronics due to large nonlinear optical coefficients and an extended transparency window. Laser processing can impose large temperature gradients, an ability that has been used to improve the uniformity of unary fibre cores, and to inscribe compositional variations in alloy systems. Interest in an integrated light-emitting element suggests a move from Group IV to III-V materials, or a core that contains both. This paper describes the fabrication of GaSb/Si core fibres, and a subsequent CO2 laser treatment that aggregates large regions of GaSb without suppressing room temperature photoluminescence. The ability to isolate a large III-V crystalline region within the Si core is an important step towards embedding semiconductor light sources within infrared light-transmitting silicon optical fibre.
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17.
  • Sørgård, T., et al. (författare)
  • Reduced loss in SiGe-core optical fibers
  • 2018
  • Ingår i: Optics InfoBase Conference Papers. - : Optical Society of America. - 9781557528209
  • Konferensbidrag (refereegranskat)abstract
    • We investigate CO2 laser processing of SiGe-core glass fibers, and show that homogeneous, low optical loss cores can be made. Coaxial Ge-rich centers within the semiconductor cores can also be fabricated.
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18.
  • Theodosiou, A., et al. (författare)
  • Characterisation of silicon fibre Bragg grating in near-infrared band for strain and temperature sensing
  • 2018
  • Ingår i: Electronics Letters. - : Institution of Engineering and Technology. - 0013-5194 .- 1350-911X. ; 54:24, s. 1393-1395
  • Tidskriftsartikel (refereegranskat)abstract
    • Fibre Bragg grating inscription in the crystalline silicon (Si)-core fibre is described using visible light femtosecond laser pulses. The femtosecond pulses at 517 nm propagate through the transparent silica glass cladding and are fully absorbed by the Si core generating locally high temperatures and stress fields in forming the grating periods. The Si FBGs were characterised in reflection, calibrated for a first time as strain and temperature sensors and compared with that of FBGs inscribed in standard silica fibres.
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19.
  • Theodosiou, A., et al. (författare)
  • Fs laser inscription of FBGs in silicon core silica clad optical fibres
  • 2017
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. ; , s. 24-25
  • Konferensbidrag (refereegranskat)abstract
    • We present results on fs laser inscription of Bragg gratings in Si-core fibres throughmodification of the silicon-glass interface; this results in stress modulation with indications ofquasi-periodic stress relief in the glass.
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20.
  • Wu, W., et al. (författare)
  • Single crystal semiconductor-core optical fiber
  • 2019
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE.
  • Konferensbidrag (refereegranskat)abstract
    • Semiconductor-core fibers are improved by removal of grain boundaries. We use a CO2 laser to process silicon-based cores; an alloying element reduces both the temperature and speed required for formation of a single crystal.
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21.
  • Ballato, John, et al. (författare)
  • Core opportunities for future optical fibers
  • 2021
  • Ingår i: JOURNAL OF PHYSICS-PHOTONICS. - : IOP Publishing. - 2515-7647. ; 3:4
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Hair-thin strands of glass, intrinsically transparent and strong, of which many millions of kilometers are made annually, connect the world in ways unimaginable 50 years ago. What could another 50 years bring? That question is the theme of this Perspective. The first optical fibers were passive low-loss conduits for light, empowered by sophisticated sources and signal processing; a second advance was the addition of dopants utilizing atomic energy levels to promote amplification, and a third major initiative was physical structuring of the core-clad combinations, using the baseline silica material. Recent results suggest that the next major expansions in fiber performance and devices are likely to utilize different materials in the core, inhomogeneous structures on different length scales, or some combination of these. In particular, fibers with crystalline cores offer an extended transparency range with strong optical nonlinearities and open the door to hybrid opto-electronic devices. Opportunities for future optical fiber that derive from micro- and macro-structuring of the core phase offer some unique possibilities in 'scattering by design'.
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22.
  • Coucheron, David A., et al. (författare)
  • Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres
  • 2016
  • Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 7
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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23.
  • Engholm, Magnus, et al. (författare)
  • On the origin of photodarkening resistance in Yb-doped silica fibers with high aluminum concentration
  • 2021
  • Ingår i: Optical Materials Express. - 2159-3930 .- 2159-3930. ; 11:1, s. 115-126
  • Tidskriftsartikel (refereegranskat)abstract
    • Ytterbium (Yb) doped silica fibers are widely used in high power fiber lasers where co-doping the silica core material with other elements is pivotal for high efficiency, lowdetrimental effects, and reliable optical properties. Aluminum (Al) is one of the most preferred co-dopants, yet, purely Yb/Al-doped silica fibers suffer from relatively high levels of photodarkening (PD) when used in laser applications. A slightly improved PD-resistance has been reported for increasing Al-doping concentration. However, the source of this improved performance is still unknown. In this article, we present the origin of the improved PD-resistance observed in Yb-doped silica fibers with high Al-concentration. It is found that a high Al-co-doping concentration reduces the interaction strength between the Yb-ion and nearby oxygen ions, resulting in a significant PD-resistance with negligible induced loss in the entire visible spectral range. A negligible PD is observed even for significantly higher Yb-concentrations than commonly used in commercially available Yb-doped silica fibers. 
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24.
  • Fokine, Michael, et al. (författare)
  • CO2 laser structuring of semiconductor-core glass fibers
  • 2014
  • Ingår i: Optics InfoBase Conference Papers. - : OSA - The Optical Society. - 9781943580194
  • Konferensbidrag (refereegranskat)abstract
    • A scanning CO2 laser system is used to process semiconductor core glass fibers. The conditions can be tuned to melt the core and soften the glass, producing resonators, tapers and bends.
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25.
  • Fokine, Michael, 1970-, et al. (författare)
  • Laser structuring, stress modification and Bragg grating inscription in silicon-core glass fibers
  • 2017
  • Ingår i: Optical Materials Express. - : Optical Society of America. - 2159-3930 .- 2159-3930. ; 7:5, s. 1589-1597
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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26.
  • Gibson, Ursula J., et al. (författare)
  • Semiconductor core fibres : materials science in a bottle
  • 2021
  • Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 12:1
  • Forskningsöversikt (refereegranskat)abstract
    • Novel core fibers have a wide range of applications in optics, as sources, detectors and nonlinear response media. Optoelectronic, and even electronic device applications are now possible, due to the introduction of methods for drawing fibres with a semiconductor core. This review examines progress in the development of glass-clad, crystalline core fibres, with an emphasis on semiconducting cores. The underlying materials science and the importance of post-processing techniques for recrystallization and purification are examined, with achievements and future prospects tied to the phase diagrams of the core materials. The application space for optical fibers is growing, enabled by fibers built using special materials and processes. In this Review, the authors discuss the materials science behind producing crystalline core fibers for diverse applications and progress in the field.
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27.
  • Hawkins, T. W., et al. (författare)
  • Kilowatt power scaling of an intrinsically low Brillouin and thermo-optic Yb-doped silica fiber
  • 2021
  • Ingår i: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 38:12, s. F38-F49
  • Tidskriftsartikel (refereegranskat)abstract
    • The performance of optical fibers is dependent on both the fiber design and the materials from which it is made. While much of the development over the past few decades has focused on fiber geometry and microstructuring, more recent analyses have shown clear benefits of addressing parasitic nonlinearities at the origins of their light–matter interactions. Reported here are results on intrinsically low Brillouin and thermo-optic core fibers, fabricated using modified chemical vapor deposition. Specifically, fibers in the Yb-doped Al2O3−P2O5−B2O3−SiO2 system are developed based on how each glass constituent affects the material parameters that enable both stimulated Brillouin scattering (SBS) and transverse mode instability (TMI). One fiber, developed to be very heavily doped, exhibited thermo-optic and Brillouin gain coefficients up to ∼3 dB and 6 dB below conventional laser fibers, respectively. A second fiber, designed to approximate a commercial double-clad laser fiber, which necessitated lower doping levels, was output power scaled to over 1 kW with an efficiency over 70% and no observed photodarkening under conventional testing. Design curves for the enabling material properties that drive TMI and SBS also are provided as functions of compositions as a tool for the community to further study and develop intrinsically low-nonlinearity fiber lasers. 
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28.
  • Huang, Meng, et al. (författare)
  • Continuous-wave Raman amplification in silicon core fibers pumped in the telecom band
  • 2021
  • Ingår i: APL PHOTONICS. - : AIP Publishing. - 2378-0967. ; 6:9, s. 096105-
  • Tidskriftsartikel (refereegranskat)abstract
    • Stimulated Raman amplification is observed for the first time in the silicon core fiber (SCF) platform. The SCFs were tapered to obtain sub-micrometer core dimensions and low optical transmission losses, facilitating efficient spontaneous scattering and stimulated Raman amplification using a continuous-wave pump source with milliwatt power levels. A maximum on-off gain of 1.1 dB was recorded at a pump power of only 48 mW with our numerical simulations, indicating that gains up to 6dB are achievable by increasing the fiber length. This work shows that the SCF platform could open a route to producing compact and robust all-fiber integrated Raman amplifiers and lasers across a broad wavelength region.
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29.
  • Huang, Meng, et al. (författare)
  • Fiber Integrated Wavelength Converter Based on a Silicon Core Fiber With a Nano-Spike Coupler
  • 2019
  • Ingår i: IEEE Photonics Technology Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1041-1135 .- 1941-0174. ; 31:19, s. 1561-1564
  • Tidskriftsartikel (refereegranskat)abstract
    • An all-fiber integrated nonlinear silicon photonic wavelength converter has been proposed and fabricated using the silicon core fiber platform. The silicon fiber was spliced directly to a conventional single mode fiber, facilitated via an inverse tapered nano-spike that helped to reduce the mode mismatch between the different core materials. Four-wave mixing-based wavelength conversion with an efficiency as high as -22.1 dB has been achieved for selected wavelengths across the C-band in a device length of only similar to 1 cm. Successful conversion of quadrature phase-shift keying signals at a 20-Gb/s bitrate, with a 1 to 2 dB penalty level at the bit error ratio (BER) = 3.8 x 10(-3), was used to demonstrate the suitability of the silicon fiber device for the construction of ultra-compact, all-fiber-based optical signal processing systems.
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30.
  • Knall, Jennifer, et al. (författare)
  • Experimental comparison of silica fibers for laser cooling
  • 2020
  • Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 45:14, s. 4020-4023
  • Tidskriftsartikel (refereegranskat)abstract
    • Laser cooling in silica has recently been demonstrated, but there is still a lack of understanding on how fiber composition, core size, and OH- contamination influence cooling performance. In this work, six Yb-doped silica fibers were studied to illuminate the influence of these parameters. The best fiber cooled by -70 mK with only 170 mW/m of absorbed pump power at 1040 nm, which corresponds to twice as much heat extracted per unit length compared to the first reported laser cooling in silica. This new fiber has an extremely low OW loss and a higher Al concentration (2.0 wt.% Al), permitting a high Yb concentration (2.52 wt.% Yb) without incurring significant quenching. Strong correlations were found between the absorptive loss responsible for heating and the loss measured at 1380 nm due to absorption by OH-. 
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31.
  • Knall, Jennifer, et al. (författare)
  • Laser cooling in a silica optical fiber at atmospheric pressure
  • 2020
  • Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 45:5, s. 1092-1095
  • Tidskriftsartikel (refereegranskat)abstract
    • For the first time, to the best of our knowledge, laser cooling is reported in a silica optical fiber. The fiber has a 21-μm diameter core doped with 2.06 wt.% YbM3+ and co-doped with Al2O3 and F- to increase the critical quenching concentration by a factor of 16 over the largest reported values for the Yb-doped silica. Using a custom slow-light fiber Bragg grating sensor, temperature changes up to -50 mK were measured with 0.33 W/m of absorbed pump power per unit length at 1040 nm. The measured dependencies of the temperature change on the pump power and the pump wavelength are in excellent agreement with predictions from an existing model, and they reflect the fiber's groundbreaking quality for the radiation-balanced fiber lasers. 
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32.
  • Song, Seunghan, et al. (författare)
  • Localised structuring of metal-semiconductor cores in silica clad fibres using laser-driven thermal gradients
  • 2022
  • Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 13:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors show that micron size fibers comprised of semiconductor and metallic materials can be purified or doped, recrystallized or have the constituents rearranged into a variety of structures with device prospects. The molten core drawing method allows scalable fabrication of novel core fibres with kilometre lengths. With metal and semiconducting components combined in a glass-clad fibre, CO2 laser irradiation was used to write localised structures in the core materials. Thermal gradients in axial and transverse directions allowed the controlled introduction, segregation and chemical reaction of metal components within an initially pure silicon core, and restructuring of heterogeneous material. Gold and tin longitudinal electrode fabrication, segregation of GaSb and Si into parallel layers, and Al doping of a GaSb core were demonstrated. Gold was introduced into Si fibres to purify the core or weld an exposed fibre core to a Si wafer. Ga and Sb introduced from opposite ends of a silicon fibre reacted to form III-V GaSb within the Group IV Si host, as confirmed by structural and chemical analysis and room temperature photoluminescence.
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33.
  • Sorgard, Trygve, et al. (författare)
  • All-optical high-speed modulation of THz transmission through silicon core optical fibers
  • 2021
  • Ingår i: Optics Express. - : The Optical Society. - 1094-4087. ; 29:3, s. 3543-3552
  • Tidskriftsartikel (refereegranskat)abstract
    • High speed optical modulation of THz radiation is of interest for information processing and communications applications. In this paper infrared femtosecond pulses are used to generate free carriers that reduce the THz transmission of silicon based waveguides over a broad spectral range. Up to 96 6 70 modulation is observed from 0.5 to 7 THz in an optical fiber with a 210 mu m diameter gold-doped silicon core. The observed carrier recombination time of 2.0 +/- 0.2 ns makes this material suitable for high speed all-optical signal processing. These results show both enhanced modulation depth and reduced carrier lifetime when compared to the performance of a high resistivity float zone silicon rectangular guide with comparable cross sectional area.
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34.
  • Sorgard, Trygve, et al. (författare)
  • Broadband infrared and THz transmitting silicon core optical fiber
  • 2020
  • Ingår i: Optical Materials Express. - : The Optical Society. - 2159-3930 .- 2159-3930. ; 10:10, s. 2491-2499
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon waveguide structures are a viable alternative for the transmission of signals over a wide range of frequencies, and new fabrication methods are key to increased applications. In this work, THz transparency of silicon-core, silica clad fibers, refined using a traveling solvent method, is demonstrated. The approximate to 200 mu m core of these fibers is shown to have good transmission from 4.8-9 mu m and 1-7 THz. Fibers were drawn on a conventional optical fiber tower using the scalable molten core technique and CO2 laser annealed, resulting in large-grain crystalline cores with broadband transmission. The spectral properties are comparable to those of rectangular guides of similar cross-sectional area cut from high resistivity float zone silicon wafers.
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35.
  • Vigneron, Pierre-Baptiste, et al. (författare)
  • Anti-Stokes Cooling of Nanoparticle-Doped Silica Fibers
  • 2022
  • Ingår i: PHOTONIC HEAT ENGINES. - : SPIE - International Society for Optical Engineering. - 9781510649088 - 9781510649071
  • Konferensbidrag (refereegranskat)abstract
    • The recent reports of laser cooling in Yb-doped aluminosilicate fibers and silica preforms have opened up the field of optical refrigeration and radiation-balanced lasers to the enormous realm of silica fiber lasers and amplifiers. To increase the cooling efficiency achieved in these materials, it is critical to identify host compositions that improve the Yb3+-ion properties in the directions of low concentration quenching, short radiative lifetime, and a long-wavelength absorption tail that extends as far as possible above the zero-phonon line. In this on-going quest, nanoparticle-doped fibers offer a promising technique to modify the chemical environment of the Yb3+ ions and achieve some of these properties. In this work, three fibers in which the Yb3+ ions are initially encapsulated in CaF2, SrF2, or BaF2 nanoparticles were fabricated using a solution-doping technique, and their laser-cooling properties evaluated experimentally and analyzed. The CaF2 fiber and the SrF2 fiber were successfully cooled at atmospheric pressure when pumped with a continuous-wave laser at the near-optimum wavelength of 1040 nm. The measured maximum temperature change from room temperature was -26.2 mK for the CaF2 fiber at a pump power absorption level of 90 mW/m, and -16.7 mK at 66 mW/m for the SrF2 fiber. The BaF2 fiber did not cool, but it warmed only slightly, indicating that it was not far from cooling. Analysis of the measured dependence of the fiber temperature change on pump power with a model enabled extraction of the fiber's critical quenching concentration and residual absorptive loss due to impurities. Comparison of these values to the values reported for an aluminosilicate fiber and fiber preforms that cooled shows that the CaF2 and SrF2 fibers faired as well as the fiber, and better than the preforms, in terms of quenching, but that they had a higher absorptive loss. This study establishes the significant research potential of nanoparticle-doped fibers in the search for efficient laser-cooling silica hosts.
  •  
36.
  • Vigneron, Pierre-Baptiste, et al. (författare)
  • Anti-Stokes fluorescence cooling of nanoparticle-doped silica fibers
  • 2022
  • Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 47:10, s. 2590-2593
  • Tidskriftsartikel (refereegranskat)abstract
    • The first observation of cooling by anti-Stokes pumping in nanoparticle-doped silica fibers is reported. Four Yb-doped fibers fabricated using conventional modified chemical vapor deposition (MCVD) techniques were evaluated, namely, an aluminosilicate fiber and three fibers in which the Yb ions were encapsulated in CaF2, SrF2, or BaF2 nanoparticles. The nanoparticles, which oxidize during preform processing, provide a modified chemical environment for the Yb3+ ions that is beneficial to cooling. When pumped at the near-optimum cooling wavelength of 1040 nm at atmospheric pressure, the fibers experienced a maximum measured temperature drop of 20.5 mK (aluminosilicate fiber), 26.2 mK (CaF2 fiber), and 16.7 mK (SrF2 fiber). The BaF2 fiber did not cool but warmed slightly. The three fibers that cooled had a cooling efficiency comparable to that of the best previously reported Yb-doped silica fiber that cooled. Data analysis shows that this efficiency is explained by the fibers' high critical quenching concentration and low residual absorptive loss (linked to sub-ppm OH contamination). This study demonstrates the large untapped potential of nanoparticle doping in the current search for silicate compositions that produce optimum anti-Stokes cooling.  
  •  
37.
  • Wu, Dong, et al. (författare)
  • Four-Wave Mixing-Based Wavelength Conversion and Parametric Amplification in Submicron Silicon Core Fibers
  • 2021
  • Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 1077-260X .- 1558-4542. ; 27:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Silicon core fibers represent a versatile platform for all-fiber integrated nonlinear optical applications. This paper describes the state of the art in four-wave mixing-based parametric amplification, and wavelength conversion in silicon fibers that have been tapered to improve the material quality, and engineer the dispersion profile. Fibers with submicron core dimensions have been fabricated, and used to demonstrate high gain parametric amplification in the C-Band, and broadband wavelength conversion extending out to the S-, and L-bands. The potential to use these fibers for all-optical signal processing of 20 Gbit/s data signals has also been demonstrated, with a robust all-fiber coupling scheme presented to improve the efficiency, and practicality of these devices. These results highlight the potential of silicon core fibers for use in nonlinear signal processing within future telecommunication systems.
  •  
38.
  • Wu, Dong, et al. (författare)
  • Net optical parametric gain in a submicron silicon core fiber pumped in the telecom band
  • 2019
  • Ingår i: APL Photonics. - : AIP Publishing. - 2378-0967. ; 4:8
  • Tidskriftsartikel (refereegranskat)abstract
    • A silicon core fiber (SCF) has been designed and fabricated with a dispersion engineered profile to support broadband optical parametric amplification across the telecom window. The combination of low optical transmission losses and high coupling efficiency of the SCF platform has allowed for an on-off optical parametric gain up to 9 dB, without experiencing gain saturation due to nonlinear absorption, resulting in a net off-waveguide gain of similar to 2 dB. The ability to splice the SCFs with conventional silica fiber systems opens a route to compact and robust all-fiber integrated optical parametric amplifiers and oscillators that could find use in telecoms systems.
  •  
39.
  • Wu, Wei, et al. (författare)
  • CO(2 )laser annealed SiGe core optical fibers with radial Ge concentration gradients
  • 2020
  • Ingår i: Optical Materials Express. - : The Optical Society. - 2159-3930 .- 2159-3930. ; 10:4, s. 926-936
  • Tidskriftsartikel (refereegranskat)abstract
    • CO2 laser annealing of SiGe core, glass-clad optical fibers is a powerful technique for the production of single-crystal cores with spatially varying Ge concentrations. Laser power, laser scan speed and cooling air flow alter the Ge distribution during annealing. In this work, near-single crystal fibers exhibiting a central axial feature with peak Ge concentration similar to 15 at% higher than the exterior of the semiconductor core have been prepared. Preferential transmission of near infrared radiation through the Ge-rich region, and spectral data confirm its role as a waveguide within the semiconductor core. This proof-of-concept step toward crystalline double-clad structures is an important advancement in semiconductor core optical fibers made using the scalable molten core method.
  •  
40.
  • Wu, Wei, et al. (författare)
  • Ge-capped SiGe core optical fibers
  • 2019
  • Ingår i: Optical Materials Express. - : OPTICAL SOC AMER. - 2159-3930 .- 2159-3930. ; 9:11, s. 4301-4306
  • Tidskriftsartikel (refereegranskat)abstract
    • CO2 laser processing offers the possibility to inscribe structures within glass-clad SiGe-core fibers by altering the spatial distribution of the Si and Ge. Spatial segregation of Ge to the end of a fiber is shown via optical transmission measurements used to alter the local bandgap, and the curved end of the fiber focuses the output of a multimode fiber. Scalable fabrication is demonstrated using a commercial CO2 laser engraver for processing of arrays.
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