Browsing by Author "Friebele, E. Joseph"

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    Fast-Neutron Radiation Effects in A Silica-Core Optical-Fiber Studied By A Ccd-Camera Spectrometer
    Griscom, D. L.; Gingerich, M. E.; Friebele, E. Joseph; Putnam, M.; Unruh, W. (Optical Society of America, 1994-05-01)
    A simple CCD-camera spectrometer was deployed at the Los Alamos Spallation Radiation Effects Facility to characterize fast-neutron irradiation effects in several silica-based optical fibers over the wavelength range approximately 450-1100 nm. The experimental arrangement allowed optical loss spectra to be developed from remotely recovered frame grabs at various times during irradiation without it being necessary to resort to cutback methods. Data recorded for a pure-silica-core/F-doped-silica-clad fiber displayed a peculiar artifact, which is described and mathematically modeled in terms of leaky modes propagating in an optical cladding that is substantially less susceptible to radiation-induced optical attenuation than is the core. Evidence from optical time-domain reflectometry supports the postulate that mode leakage into the cladding may be a result of light scattering from the tracks of ions displaced by the 14-MeV neutrons. These results suggest that fibers with fluorine doping in the core, as well as in the cladding, would be relatively resistant to radiation-induced attenuation in the UV-visible spectral region.
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    Stress-dependent growth kinetics of ultraviolet-induced refractive index change and defect centers in highly Ge-doped SiO2 core fibers
    Tsai, Tsung-Ein; Taunay, Thierry; Friebele, E. Joseph (AIP Publishing, 1999-10-01)
    The evolution of the index change of type-IIa gratings observed in 28 mol % Ge-SiO2 core fibers with 1.8 mu m core diameter under various strains was measured from the optical spectra, and the induced defects at high and low strains were studied with electron spin resonance. Data will be presented to show that the index modulation (Delta n(mod)) of type-IIa gratings is likely associated with Ge E-' centers. (C) 1999 American Institute of Physics. [S0003-6951(99)04141-8].
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    Structural origin of the 5.16-EV optical-absorption band in silica and GE-doped silica
    Tsai, Tsung-Ein; Friebele, E. Joseph; Rajaram, M.; Mukhapadhyay, S. (AIP Publishing, 1994-03-01)
    The origin of the 5.16 eV absorption band observed in silica and Ge-doped silica was studied using optical and electron spin resonance (ESR) measurements. The band was observed only in samples containing Ge, suggesting that it is related to the Ge impurity in silica, while a lack of correlation between the ESR intensity of the induced hydrogen-associated doublet and the absorption coefficient of the 5.16 eV band indicates that it is not related to two-coordinated Si or Ge. The observation of the absorption coefficient increased as the square root of the Ge concentration demonstrates that the 5.16 eV band is not related to two-coordinated Ge defects but that it is an oxygen deficiency center of the divacancy type associated with Ge.
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    Uniform component of index structure induced in Ge-SiO2 fibers by spatially modulated ultraviolet light
    Tsai, Tsung-Ein; Williams, Glen M.; Friebele, E. Joseph (AIP Publishing, 1998-06-01)
    Experimental data are presented to show that Ge(1) and Ge(2) centers are induced by trapping photoinduced electrons from the conduction band, in agreement with our previous proposal that both are trapped electron centers. The spacing (Lambda) dependence of ultraviolet (UV) light bleaching of the pre-existing Ge E' centers illustrates that the electron diffusion length is greater than Lambda of the spatially modulated UV light used in the fabrication of fiber Bragg gratings (FBGs) with Bragg wavelengths less than or equal to 1.5 mu m (short period grating) for laser powers as low as 25 mJ/cm(2). The Ge(1) and Ge(2) centers are uniformly induced by the spatially modulated UV light and therefore contribute to the uniform component of the index structure of FBGs. [S0003-6951(98)01325-4].