Fiber & ElectroOptics Research Center (FEORC)

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Characterization And Modeling Of Drift Noise in Fourier Transform Spectroscopy: Implications For Signal Processing And Detection Limits
Hazel, G.; Bucholtz, F.; Aggarwal, I. D. (Optical Society of America, 1997-05-01)
A theoretical analysis of long-term drift noise in Fourier transform spectroscopy is presented. Theoretical predictions are confirmed by experiment. Fractional Brownian motion is employed as a stochastic process model for drift noise. A formulation of minimum detectable signal is given that properly accounts for drift noise. The spectral exponent of the low-frequency drift noise is calculated from experimental data. A frequency-dependent optimal spectrum averaging time is found to exist beyond which the minimum detectable signal increases indefinitely. It is also shown that the minimum detectable signal in an absorbance or transmission measurement degrades indefinitely with the time elapsed since background spectrum acquisition. (C) 1997 Optical Society of America.
Dynamics of the 5-EV optical-absorption in SIO2 glass
Tsai, T. E.; Jewell, J. M.; Sanghera, J. S. (AIP Publishing, 1993-06-01)
The optical absorption at 5 eV in SiO2 glass was observed, using laser calorimetry, to change reversibly depending on the intensity of UV light. The generation and bleaching of an absorption band at 5 eV by two- and one-photon absorption processes, respectively, can explain these reversible changes. This observation supports the structural model of unrelaxed oxygen deficiency center for the 5 eV absorption band in silica.
Layer-by-layer electrostatic self-assembly of nanoscale Fe3O4 particles and polyimide precursor on silicon and silica surfaces
Liu, Y. J.; Wang, Anbo; Claus, Richard O. (AIP Publishing, 1997-10-01)
Monolayer and multilayer ultrathin films comprised of nanosized iron oxide (Fe3O4) particles and polyimide molecules have been fabricated on single crystal silicon and quartz substrates by a novel layer-by-layer electrostatic self-assembly process. This process involves the alternate dipping of a substrate into an aqueous solution of anionic polyimide precursor (polyamic acid salt, PAATEA), followed by dipping into an aqueous solution of polycation polydiallyldimethylammonium chloride (PDDA) which coats on nanoscale Fe3O4 particles as a stabilizer. The growth process and the structure have been characterized using UV-vis spectroscopy, contact angle, and ellipsometry measurements. The results suggest that well-ordered uniform monolayer and multilayer magnetic films have been formed on silicon and silica surfaces. A recently developed highly sensitive fiber optic magnetic field sensor was used to probe the small magnetic field intensity produced by the multilayer films. (C) 1997 American Institute of Physics.
Separation of Intrinsic and extrinsic Optical-Absorption in a Fluoride Glass
Jewell, J. M.; Williams, Glen M.; Jaganathan, J.; Aggarwal, I. D.; Greason, P. (AIP Publishing, 1991-07-01)
The contribution of impurity ions to the total optical absorption of a heavy metal fluoride glass has been determined at 532 and 1064 nm. Four ZrF4-BaF2-LaF3-AlF3-NaF glasses were prepared from various purity raw materials. The absorption coefficients of these glasses range from 0.92 to 45.4 x 10(-4) cm-1 at 1064 nm and from 7.43 to 11.1 X 10(-4) cm-1 at 532 nm as determined by laser calorimetry. The concentrations of Fe, Ni, Cu, and Co ions in each glass were determined by graphite furnace atomic absorption spectroscopy. These two measurements enable the absorption, due to transition metal ions to be differentiated from the intrinsic absorption of the glass. At 1064 nm, the absorption coefficient of these glasses is controlled entirely by the transition metal ion content. However, at 532 nm, the absorption by the transition metal ions accounts for 4-42% of the total absorption depending on impurity concentration. The intrinsic absorption of this fluoride glass calculated from these data at 532 nm is (7.69 +/- 0.99) X 10(-4) cm-1.
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].
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.
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].

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