N N Vechkanov

Ultraviolet absorption and excess optical loss in preforms and fibers with high-germanium content

Nature of excess optical loss in fibers with high (up to 35 mol.%) GeO2 content silica core was studied experimentally. The absorption and scattering loss dependences on the drawing conditions were studied as well as the behavior of germanium-related oxygen- deficient centers (GODC) absorbing in UV spectral region. The peculiarity of such fibers was found to be in the drastic increase of the absorption and scattering loss when the core diameter diminish up to 3-3.5 micrometers . According to the excess loss analysis the absorption loss is caused by the enhanced GODC formation and the Ge-related drawing-induced defects. The excess scattering loss which dominates is assumed to be due to azimuthal and longitudinal core inhomogeneities caused by hydrodynamical instabilities of viscous glass during the fiber drawing. The germanium diffusion effect on optical loss is discussed.

Al-free core composition bismuth-doped optical fibre with luminescence band at 1300 nm

Fabrication technique and spectroscopic study of MCVD Bi-Na-doped phosphosilicate glass core optical fibres are discussed. The fibres reveal a broadband luminescence with the maximum in 1300 nm range.

Photorefractive effect and photoinduced χ(2) grating formation in germanosilicate core fibers codoped with nitrogen in MCVD process

Single-mode germanosilicate-core optical fibers were fabricated by the MCVD process modified by sintering of the deposited soot in a reduced atmosphere (helium- or nitrogen- containing one). The fibers showed a higher photoinduced refractive index change and a higher efficiency of (chi) (2) formation as compared to an ordinary germanosilicate fiber. The sintering process in nitrogen and helium atmospheres was shown to increase the concentration of germanium oxygen-deficient centers. Besides, nitrogen appears to enter into the glass network in a sufficient concentration to modify the glass network and to additionally increase photosensitivity of the fibers.