Germano-silicate Glass Fiber Research Articles

Fabrication and Gamma-Ray Irradiation Effect on Optical and Mechanical Properties of Germano-Silicate Glass Fibers with Inner Cladding of B and F Doped Silica Glasses

ABSTRACTThe effect of glass composition, pure silica glass, boron-doped and fluorine-doped silica glasses of inner cladding, in the germano-silicate glass core fibers on optical and mechanical properties upon the γ-ray irradiation was investigated. Enhanced radiation hardening at 1,550 nm was found in both the B- and F-doped fibers after the γ-ray irradiation with dose-rate of 1.25 kGy/h. The radiation-induced attenuation (RIA) was found to increase in the order of the B-doped fiber, the F-doped fiber, and the silica fiber. While no major influence on the refractive index of the fibers after the γ-ray irradiation was found, the residual stress was slightly changed.

New radiation colour centre in germanosilicate glass fibres

We have investigated radiation-induced absorption (RIA) of light in five optical fibres with a germanosilicate core and a light-reflecting cladding made of undoped silica glass in the visible and near-IR ranges under γ-irradiation to a dose of 1 kGy at temperatures from −60 to +60 °C. The concentration of GeO2 in the cores of the studied fibres ranged from 3.5 to 50 mol%. It is found that the RIA dependences on temperature for optical fibres having been lightly or heavily doped by germanium are different. An increase in RIA with increasing temperature for heavily doped fibres is associated with an increase in the absorption intensity of the GeX centre due to thermal decay of Ge(1) centre. It is found that, in fibres lightly doped by germanium, RIA in the near-IR range is determined mainly by a previously unknown radiation colour centre (RCC) called the GeY centre, with a maximum of the absorption band at a wavelength of ∼900 nm (1.38 eV), a half-width of 495 nm (0.71 eV), and an activation energy of 0.15 eV. It is established that the concentrations of GeX and GeY centres differently depend on the irradiation temperature and the content of germanium in silica glass: the concentration of GeX centres increases and the concentration of GeY centers, on the contrary, decreases with increasing temperature and GeO2 concentration in the core. Thus, in accordance with its spectral position, the GeY centre represents the main RCC limiting the radiation resistance of standard telecommunication fibres with a small addition of germanium (3.5 mol % of GeO2).

Origin of near-infrared luminescence in Bismuth-doped silica and germanosilicate glass fibers: Crystal field modeling

Bismuth-doped silica-based glasses have already been proved to be promising materials for the fiber lasers and amplifiers operating in the near-infrared (NIR) spectral region. However, the development of such devices, which would have eligible efficiency, is impossible without a solid understanding of the NIR emitting center's nature. In the present work, based on the crystal field calculations we demonstrate that in silica and germanosilicate glasses this center is a univalent Bi ion affected by a rather strong local crystal field. According to our results, a transition from the first excited state to the ground state in Bi+ causes the famous NIR photoluminescence. The relatively high degree of reduction of the spin-orbit coupling constant indicates, most probably, the formation of weak covalent bonding of Bi+ with ions of the environment.

Effect of Zn Addition on Non-Resonant Third-Order Optical Nonlinearity of the Cu-Doped Germano-Silicate Optical Glass Fiber

Cu/Zn-codoped germano-silicate optical glass fiber was manufactured by using the modified chemical vapor deposition (MCVD) process and solution doping process. To investigate the reduction effect of Zn addition on Cu metal formation in the core of the Cu/Zn-codoped germano-silicate optical glass fiber, the optical absorption property and the non-resonant third-order optical nonlinearity were measured. Absorption peaks at 435 nm and 469 nm in the Cu/Zn-codoped germano-silicate optical glass fiber were contributed to Cu metal particles and ZnO semiconductor particles, respectively. The effective non-resonant optical nonlinearity, gamma, of the Cu/Zn-codoped germano-silicate optical glass fiber was measured to be 1.5097 W(-1) x km(-1) by using the continuous-wave self-phase modulation method. The gamma of the Cu/Zn-codoped germano-silicate optical glass fiber was about four times larger than that of the reference germano-silicate optical glass fiber without any dopants. The increase of the effective non-resonant optical nonlinearity, gamma, of the Cu/Zn-codoped germano-silicate optical glass fiber, can be attributed to the enhanced nonlinear polarization due to incorporated ZnO semiconductor particles and Cu metal ions in the glass network. The Cu/Zn-codoped germano-silicate optical glass fiber showed high nonlinearity and low transmission loss at the optical communication wavelength, which makes it suitable for high-speed-high-capacity optical communication systems.

Effect of fluorine doping on the optical loss in MCVD fibers based on heavily doped germanosilicate glass

We have studied the size distribution of silica glass particles in the fabrication of heavily doped germanosilicate glass fiber preforms by modified chemical vapor deposition (MCVD) at different Freon 113 concentrations in the gas mixture. The addition of Freon 113 to the gas mixture is shown to reduce the particle size in the deposited core glass layer and the optical loss in the fiber. A mechanism is proposed which accounts for the effect of the initial particle size in the core glass layer on the anomalous scattering and total optical loss in heavily doped step- and graded-index fibers.

Tellurium-enhanced nonresonant third-order optical nonlinearity in a germanosilicate optical fiber

A tellurium-doped germanosilicate optical fiber was developed by modified chemical vapor deposition and solution doping techniques. Using the continuous-wave self-phase modulation method, the nonresonant nonlinear refractive index, n2, was measured to be 5.52 x 10(-20) m2/W, which is 2 to 3 times that of the undoped germanosilicate glass fiber. Polyhedron structures TeO3 and TeO4 with GeO4 and SiO4 are believed responsible for lower phonon energy, more nonbridging oxygens, and a larger hyperpolarization, leading to the observed higher nonresonant optical nonlinearity.

Visible Optical Limiting Property of Germano-Silicate Glass Fibers with Au Nanoparticles Incorporated

Investigating with a continuous-wave 488-nm argon-ion laser, we rstly report on the visible optical limiting properties of germano-silicate optical bers with gold nanoparticles incorporated. The ground-state conduction, the surface plasmon band and the free carrier band were considered as a three-level model to theoretically explain the obtained optical limiting behaviors. In the visible wavelength region around the surface plasmon resonance absorption peak of the gold nanoparticles, the e ective nonlinear absorption coe cient was estimated to be 22.4 cm/GW.

Determination of the non-resonant non-linear refractive index of germano-silicate glass fiber with an arbitrary GeO2 concentration profile

We propose a new method to measure the non-resonant third-order optical non-linearity of germano-silicate glass fiber having arbitrary GeO2 concentration profile using wavelength dependence of mode field diameter. The measured non-linear refractive indices of Samsung’s single mode fiber and the Sumitomo’s highly non-linear optical fiber were found to be in good agreement with the published results within 3.2% and 3.1% error, respectively. The method is applicable only for the optical fibers whose dispersion is dominated by the material dispersion.

Au-nanoparticle-incorporated germano-silicate glass fiber with high resonant nonlinearity

To investigate the nonlinear optical properties of metallic nanoparticles in dielectric composite materials, germano-silicate glass optical fibers incorporated with gold nanoparticles were made by using modified chemical vapor deposition technique and solution doping process. The incorporation of the gold nanoparticles was confirmed by the sharp absorption peak appeared near 498.4nm, which was due to the surface plasmon resonance absorption of Au nanoparticles. Resonant optical nonlinearities of the fibers were estimated by measuring the peak shift of the fringes obtained from the long-period fiber grating pair upon pumping with Argon laser at 488nm. The resonant nonlinearity was found to be 5.00×10 -16 m 2 /W by the incorporation of the gold metal concentration and with the addition of Al 3+ ions.

Visible to infrared photoluminescence from gold nanoparticles embedded in germano-silicate glass fiber

Germano-silicate glass fiber containing gold nanoparticles was developed by modified chemical vapor deposition and solution doping processes. Pumping with 488 nm Argon ion laser, we firstly report on the visible to infrared photoluminescence of the gold nanoparticles embedded in the core of the germano-silicate fibers. The surface plasmon resonance absorption peak at 498.4 nm and the visible to infrared photoluminescence over the range of 600 nm approximately 1560 nm were found and explained according to the interband and intraband electronic transitions of Au atoms. The averaged quantum efficiencies of the photoluminescence at 833 nm and 1536 nm were estimated to be 5.75 x 10(-8) and 2.01 x 10(-9), respectively.

Cu^2+-doped germano-silicate glass fiber with high resonant nonlinearity

We firstly report on the fabrication of Cu(2+)-doped germano-silicate glass fiber for nonlinear optical devices application by using modified chemical vapor deposition and solution doping processes. Broadband absorption near 700nm due to the 3d-shell electron transitions of Cu(2+) ions from the ground state to the excited states was observed. The resonant nonlinearity of the Cu(2+)-doped fiber was estimated to be 5.5x10(-17)m(2)/W by measuring the phase shift of the fringes obtained from the long-period fiber grating pair upon pumping with a laser diode at 980nm and non-resonant nonlinearities were also measured to be 4.114x10(-21)m(2)/W by the continuous wave self-phase modulation method.

Absorption and emission properties of Tm2+ ions in germanosilicate glass fibers

Absorption and emission properties between 350nm and 1600nm of the Tm2+ ions in optical fibers were investigated using the Tm2+-Tm3+ co-doped germanosilicate glass fibers and its fiber preform. Strong broad absorption band due to Tm2+ ions was found to appear from 350nm to ~900nm together with the absorption bands due to Tm3+ ions. Broad emission from ~600nm to ~1050nm and the other emission from ~1050nm to ~1300nm, which were not shown in the Tm3+ ions, were found upon the Ar ion laser pumping at 515nm. Both absorption and emission results confirm that the Tm2+ ions in the germanosilicate glass have the 4f-5d energy band from 350nm to ~900nm and the 4f-4f energy level at ~1115nm.

Gain optimization of germanosilicate fiber Raman amplifier and its applications in the compensation of Raman-induced crosstalk among wavelength division multiplexing channels

Spectral characteristics of the stimulated Raman scattering (SRS) process were theoretically investigated for step-index silica optical fibers with various GeO/sub 2/ concentrations. Optimal-fiber lengths and germanium concentration, where the first Stokes power reaches maximum, were calculated at various pump power levels for application in Raman amplifiers. Based on this analysis, we proposed and experimentally demonstrated a new channel-equalizing technique to simultaneously compensate Raman-induced crosstalk and amplify wavelength-division-multiplexing (WDM) signals using a discrete Raman amplifier in the 1.5-/spl mu/m range. As a further application of SRS in germanosilicate glass fibers, we introduce an all-optical variable attenuator for channel equalization that could be used in dynamic optical power tilt control in WDM systems.

Second order diffraction efficiency of Bragg gratings written within germanosilicate fibres

Second order diffraction has been observed from Bragg gratings written within germanosilicate glass fibres. Experimental results are reported on the evolution of the first and the second order Bragg grating reflectivities as function of the uv laser shot number used for the inscription. Second order diffraction can be detected once the first order grating reflectivity has begun to saturate. Possible explanations of the second order grating formation are discussed. Our experimental results are consistent with a saturation in the photo-induced change in refractive index.

Direct observation of UV induced bleaching of 240 nm absorption band in photosensitive germanosilicate glass fibres

Ultraviolet loss measurements on germanosilicate fibre samples showing an intense absorption, centred at 242 nm, with an associated fluorescence at 413 nm are presented. The first direct observation is reported of the bleaching of this 240 nm band under the action of ultraviolet irradiation, evidence which is consistent with the Kramers-Kronig model for the photosensitive refractive index change in these glasses.

Birefringence caused by thermal stress in elliptically deformed core optical fibers

Birefringence and polarization dispersion introduced by thermal stress in single-mode fibers with elliptical core are formulated here in terms of fiber structure parameters, thermal expansion coefficients, and thermoelastic constants. Thermal stress distribution and birefringence characteristics are estimated within first-order perturbation with respect to fiber core ellipticity. Normalized frequency dependence of birefringence and polarization dispersion is also derived in this paper. Birefringence and polarization dispersion in elliptical core fiber are seen to depend on thermal stress rather than geometrical anisotropy for relatively small relative index differences. Numerical examples are presented for germanosilicate, borosilicate, and phosphosilicate glass fibers.