M. Yu. Salganskii

High-aperture optical waveguides based on fluorine-doped silica glass

The dependence of fluorine incorporation into silica glass on conditions of the optical waveguide blank manufacture using the method of modified chemical vapor deposition (MCVD) is studied. The degree of fluorine incorporation at constant consumption of a fluoridizer (SiF4) is shown to increase with an increase in the volume of deposited material. Samples of multimode optical waveguides with a core from pure silica glass and a reflective coating made of fluorine-doped silica glass with a numerical aperture of ∼0.18 are obtained. Optical losses in such optical waveguides reach 0.5 dB/km in the long-wavelength region of the spectrum.

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.

GeO2-rich low-loss single-mode optical fibers

We have optimized the MCVD process for the fabrication of single-mode optical fibers with a heavily doped (up to 30 mol % GeO2) core for Raman lasers and amplifiers. Removing the central index dip in the core, we were able to reduce the optical losses in such fibers to the lowest level for the MCVD technology.

Reaction of Germanium Tetrachloride with Oxygen under MCVD Fiber Preform Fabrication Conditions

The GeO2 yield in the reaction between GeCl4 and oxygen has been determined as a function of the reaction time under typical MCVD fiber preform fabrication conditions. It is shown that the yield increases steadily over time and may attain 100%. In the case of the cooxidation of germanium and silicon tetrachlorides under the same conditions, there is an optimal reaction time corresponding to a maximum in GeO2 yield. The temperature profile along the reaction zone has been optimized in terms of germania yield.

Three-photon spontaneous downconversion in highly nonlinear germania-silica optical fiber waveguides

Three-photon spontaneous parametric downconversion (TPSPDC) is a challenging problem in nonlinear quantum optics. A highly doped germania-silica optical fiber is a good candidate for the appropriate nonlinear medium, because of the big interaction length and tight field confinement. A principal condition for TPSPDC is the exact phase-matching between the pump and signal fiber modes.

Influence of fibre design and curvature on crosstalk in multi-core fibre

We have studied the influence of cross-sectional structure and bends on optical cross-talk in a multicore fibre. A reduced refractive index layer produced between the cores of such fibre with a small centre-to-centre spacing between neighbouring cores (27 μm) reduces optical cross-talk by 20 dB. The cross-talk level achieved, 30 dB per kilometre of the length of the multicore fibre, is acceptable for a number of applications where relatively small lengths of fibre are needed. Moreover, a significant decrease in optical cross-talk has been ensured by reducing the winding diameter of multicore fibres with identical cores.

Polarizing very-large-mode-area bragg fiber

Single-mode larger-mode-area (LMA) all-glass (free of air-holes) fibers are required for all-fiber high-power lasers and amplifiers as they allow for efficient splicing with other components, which is impossible in the case of LMA photonic crystal fiber. Recently, we have demonstrated an active all-glass Bragg fiber with a mode-field diameter of 26 µm (λ=1.04 µm) [1]. Single-mode transverse mode-oscillation was achieved both in the straight and in the bent fiber (at bend radii larger than 7.5 cm) owing to differential mode gain. In this communication, we propose a Bragg fiber design including a microstructured core in order to increase further the mode-field diameter.

Photonic bandgap fibers for high-power CW and pulsed applications

In the reach for high-power large mode area (LMA) fibers are routinely used. Photonic bandgap fibers can be engineered so that a single mode can be propagated in a large core fiber. High-power CW or pulsed bandgap lasers can then be elaborated.

Optical losses in single-mode and multimode fibres heavily doped with GeO{sub 2} and P{sub 2}O{sub 5}

Optical losses in single-mode and multimode optical fibres heavily doped with germanium oxide and phosphorus oxide are studied. Optical losses in multimode fibres in a broad spectral range are found to be much lower than in single-mode fibres with the same concentration of dopants. The study of few-mode fibres showed that the core — cladding interface is the region of excess optical losses. The reasons for the observed relation between optical losses in single-mode and multimode fibres are discussed.