1,115 research outputs found

    Coupled experiment/simulation approach for the design of radiation-hardened rare-earth doped optical fibers and amplifiers

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    We developed an approach to design radiation-hardened rare earth -doped fibers and amplifiers. This methodology combines testing experiments on these devices with particle swarm optimization (PSO) calculations. The composition of Er/Yb-doped phosphosilicate fibers was improved by introducing Cerium inside their cores. Such composition strongly reduces the amplifier radiation sensitivity, limiting its degradation: we observed a gain decreasing from 19 dB to 18 dB after 50 krad whereas previous studies reported higher degradations up to 0°dB at such doses. PSO calculations, taking only into account the radiation effects on the absorption efficiency around the pump and emission wavelengths, correctly reproduce the general trends of experimental results. This calculation tool has been used to study the influence of the amplifier design on its radiation response. The fiber length used to ensure the optimal amplification before irradiation may be rather defined and adjusted to optimize the amplifier performance over the whole space mission profile rather than before integration in the harsh environments. Both forward and backward pumping schemes lead to the same kind of degradation with our active fibers. By using this promising coupled approach, radiation-hardened amplifiers nearly insensitive to radiations may be designed in the future

    Design of Radiation-Hardened Rare-Earth Doped Amplifiers Through a Coupled Experiment/Simulation Approach

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    We present an approach coupling a limited experimental number of tests with numerical simulations regarding the design of radiation-hardened (RH) rare earth (RE)-doped fiber amplifiers. Radiation tests are done on RE-doped fiber samples in order to measure and assess the values of the principal input parameters requested by the simulation tool based on particle swarm optimization (PSO) approach. The proposed simulation procedure is validated by comparing the calculation results with the measured degradations of two amplifiers made with standard and RH RE-doped optical fibers, respectively. After validation, the numerical code is used to theoretically investigate the influence of some amplifier design parameters on its sensitivity to radiations. Simulations show that the RE-doped fiber length used in the amplifier needs to be adjusted to optimize the amplifier performance over the whole space mission profile rather than to obtain the maximal amplification efficiency before its integration in the harsh environment. By combining this coupled approach with the newly-developed RH RE-doped fibers, fiber-based amplifiers nearly insensitive to space environment may be designed in the future

    Radiation hardening techniques for rare-earth based optical fibers and amplifiers

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    Er/Yb doped fibers and amplifiers have been shown to be very radiation sensitive, limiting their integration in space. We present an approach including successive hardening techniques to enhance their radiation tolerance. The efficiency of our approach is demonstrated by comparing the radiation responses of optical amplifiers made with same lengths of different rare-earth doped fibers and exposed to gamma-rays. Previous studies indicated that such amplifiers suffered significant degradation for doses exceeding 10 krad. Applying our techniques significantly enhances the amplifier radiation resistance, resulting in a very limited degradation up to 50 krad. Our optimization techniques concern the fiber composition, some possible pre-treatments and the interest of simulation tools used to harden by design the amplifiers. We showed that adding cerium inside the fiber phosphosilicate-based core strongly decreases the fiber radiation sensitivity compared to the standard fiber. For both fibers, a pre-treatment with hydrogen permits to enhance again the fiber resistance. Furthermore, simulations tools can also be used to improve the tolerance of the fiber amplifier by helping identifying the best amplifier configuration for operation in the radiative environment

    Direct ultrafast laser written C-band waveguide amplifier in Er-doped chalcogenide glass

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    This paper reports the fabrication and characterization of an ultrafast laser written Er-doped chalcogenide glass buried waveguide amplifier; Er-doped GeGaS glass has been synthesized by the vacuum sealed melt quenching technique. Waveguides have been fabricated inside the 4 mm long sample by direct ultrafast laser writing. The total passive fiber-to-fiber insertion loss is 2.58 +/- 0.02 dB at 1600 nm, including a propagation loss of 1.6 +/- 0.3 dB. Active characterization shows a relative gain of 2.524 +/- 0.002 dB/cm and 1.359 +/- 0.005 dB/cm at 1541 nm and 1550 nm respectively, for a pump power of 500 mW at a wavelength of 980 nm. (C) 2012 Optical Society of Americ

    Fiber Lasers and Their Medical Applications

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    Advancing of photonics, aided with fruitful and abundant experimental and theoretical studies, over the last four decades has brought about the invention of a large variety of lasers. Among them one of the most popular types is a fiber laser, which is a variation of the standard solid-state laser, with the medium being a clad fiber waveguide structure and different dopants inside core serve as a gain media. They were derived from erbium-doped fiber amplifiers, which are still important component for telecommunications. Since discovery, fiber laser has become a natural choice for many uses, primarily because of the physical characteristics of fiber waveguide structure. Their rapid progress may show how excellent they really are. Although fiber lasers are today widely used in various research and industrial areas, one of the most meaningful applications of fiber laser technology has been through its use in medicine. A wide variety of wavelengths generated by fiber lasers as well as the diversity of physical mechanisms employed in pulse generation also additionally underpins the flexibility of fiber laser technology. This study is devoted to background technology of fiber lasers in the light of medical applications. Basic physics and theories of optical fibers and their important properties are introduced

    Spectral Engineering of Optical Fiber Through Active Nanoparticle Doping

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    The spectral engineering of optical fiber is a method of intentional doping of the core region in order to absorb/emit specific wavelengths of light therby providing enhanced performance over current fibers. Efforts here focused on developing an understanding of optically active nanoparticles based on alkaline earth fluorides that could be easily and homogeneously incorporated into the core of a silica based optical fiber preform and result in efficient and tailorable spectral emissions. Doped and undoped calcium, strontium and barium fluoride nanoparticles were successfully synthesized and characterized for their physical, chemical, and optical behavior. Distinct spectroscopic differences as a result of different host materials, varying rare earth doping levels and processing conditions, indicated the ability to influence the spectral behavior of the doped nanoparticle. By using photoluminescence to predict diffusion behavior, the application of a simple one dimensional model for diffusion provided a method for predicting the diffusion coefficient of europium ions in alkaline earth fluorides with order of magnitude accuracy. Modified chemical vapor deposition derived silica preforms were individually solution doped with europium doped alkaline earth fluoride nanoparticles. By using the rare earth doped alkaline earth fluoride nanoparticles as the dopant materials in the core of optical fiber preforms, the resultant optical properties of the glass were significantly influenced by their presence in the core. The incorporation of these rare earth doped alkaline earth fluoride nanoparticles was found to significantly influence the local chemical and structural environment about the rare earth ion, demonstrated homogeneity and uniform distribution of the rare earth dopant and resulted in specifically unique spectral behavior when compared to conventional doping methods. A more detailed structural model of the doped core glass region has been developed based on the spectral behavior of these active fiber preforms. It has been shown that rare earth doping of alkaline earth fluoride nanoparticles provides a material which can be `tuned\u27 to specific applications through the use of different host materials, processing conditions and doping levels of the rare earth and when used as dopant materials for active optical fibers, provides a means to tailor the optical behavior

    Optical Characterization of Rare Earth Doped Glasses

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    Optical amplifiers are highly sought-after in optical communications to power boost light signals carrying information. Rare Earth doped glasses have been the medium of choice for optical amplification. It is, therefore, essential to understand the interaction of light with potential host glasses for rare-earths before they could be proposed as suitable candidates. In this research, we have optically characterized three different rare earth doped bulk glasses. The glass samples investigated were Neodymium doped Gallium Lanthanum Sulfide (GLS:Nd), Erbium doped Germanium Gallium Sulfide (GeGaS:Er) and Erbium doped Fluorochlorozirconate (FCZ:Er). The transmission spectra, T(λ), was used in identifying the absorption transitions of rare earth ions from the ground level to the various excited levels and in obtaining the optical absorption coefficient, α(λ). This in turn was used in determining the Judd-Ofelt parameters, which were then used in obtaining radiative lifetimes of the energy levels of interest. Photoluminescence emission bands were also identified and their shapes were investigated. Finally, a comparison of the Judd-Ofelt lifetime with the experimental decay time was also done. From which, the major decay mechanism of the rare earth ions from the energy level under investigation was concluded

    Recent advances in radiation-hardened fiber-based technologies for space applications

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    International audience; In this topical review, the recent progress on radiation-hardened fiber-based technologies is detailed, focusing on examples for space applications. In the first part of the review, we introduce the operational principles of the various fiber-based technologies considered for use in radiation environments: passive optical fibers for data links, diagnostics, active optical fibers for amplifiers and laser sources as well as the different classes of point and distributed fiber sensors: gyroscopes, Bragg gratings, Rayleigh, Raman or Brillouin-based distributed sensors. Second, we describe the state of the art regarding our knowledge of radiation effects on the performance of these devices, from the microscopic effects observed in the amorphous silica glass used to design fiber cores and cladding, to the macroscopic response of fiber-based devices and systems. Third, we present the recent advances regarding the hardening (improvement of the radiation tolerance) of these technologies acting on the material, device or system levels. From the review, the potential of fiber-based technologies for operation in radiation environments is demonstrated and the future challenges to be overcome in the coming years are presented

    Classe de Ciências

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    info:eu-repo/semantics/publishedVersio

    Rare-earth ion doped chalcogenide waveguide amplifiers

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    Chalcogenide glass waveguide devices have received a great deal of attention worldwide in the last few years on account of their excellent properties and potential applications in mid-infrared (MIR) sensing and all-optical signal processing. Waveguide propagation losses, however, currently limit the potential for low power nonlinear optical processing, and the lack of suitable on chip integrated MIR sources is one of the major barriers to integrated optics based MIR sensing. One approach to overcome the losses is to employ rare-earth ion doped waveguides in which the optical gain can compensate the loss, in such a way that the conversion efficiency of nonlinear effects is increased significantly. For infrared applications, the long wavelengths potentially attainable from rare-earth ion transitions in chalcogenide hosts are unique amongst glass hosts. New rare-earth ion doped chalcogenide sources in the MIR range could benefit molecular sensing, medical laser surgery, defence etc. Despite these promising applications, until now, no one has succeeded in fabricating rare-earth ion doped chalcogenide amplifiers or lasers in planar devices. This work develops high quality erbium ion doped chalcogenide waveguides for amplifier and laser applications. Erbium ion doped As2S3 films were fabricated using co-thermal evaporation. Planar waveguides with 0.35 dB/cm propagation loss were patterned using photolithography and plasma etching on an erbium ion doped As2S3 film with an optimised erbium ion concentration of 0.45x1020 ions/cm3. The first demonstration of internal gain in an erbium ion doped As2S3 planar waveguide was performed using these waveguides. With different film deposition approaches, promising results on intrinsic lifetime of the Er3+ 4I13/2 state were achieved in both ErCl3 doped As2S3 films (2.6 ms) and radio frenquency sputtered Er3+:As2S3 films (2.1 ms), however, no waveguide was fabricated on these films due to film quality issues and photopumped water absorption issues. The low rare-earth ion solubility of As2S3 is considered the main factor limiting its performance as a host. Gallium-containing chalcogenide glasses are known to have good rare-earth ion solubility. Therefore, a new glass host material, the Ge-Ga-Se system, was investigated. Emission properties of the bulk glasses were studied as a function of erbium ion doping. A region between approximately 0.5 and 0.8 at% of Er3+ ion was shown to provide sufficient doping, good photoluminescence and adequate lifetime to envisage practical planar waveguide amplifier devices. Ridge waveguides based on high quality erbium ion doped Ge-Ga-Se films were patterned. Significant signal enhancement at 1540 nm was observed and 50 % erbium ion population inversion was obtained, in waveguides with Er3+ concentration of 1.5x1020 ion/cm3. To the Author's knowledge, this is the highest level of inversion ever demonstrated for erbium ions in a chalcogenide glass host and is an important step towards future devices operating at 1550 nm and on the MIR transitions of erbium ions in chalcogenide glass hosts. Photoinduced absorption loss caused by upconversion products in the waveguides is the remaining hurdle to achieving net gain. Further research is needed to find suitable compositions that possess high rare-earth ion solubility whilst avoiding the detrimental photoinduced losses
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