Using neighboring cores with different mode propagation constants (indexes) is a well-known way to reduce crosstalk in multicore fiber (MCF). However, in actual field-deployed fiber, random bends can cause a reduction in the difference between the mode indexes of neighboring cores, which consequently increases crosstalk. The level of crosstalk induced by bending in both rectangular cross-section and circular cross-section heterogeneous MCF with cores arranged in a line was investigated. The experimental results obtained indicate that in contrast to circular cross-section MCF, no bending-induced crosstalk occurs in rectangular cross-section MCF wound on the mandrel without special control of cross-section orientation. Thus, to eliminate undesirable bending-induced crosstalk in heterogeneous MCF a rectangular cross-section should be employed.
We describe composite optical fibers with rare-earth co-doped phosphate-glass core in a silica-glass cladding. High RE-ion concentrations in the phosphate core of the composite fiber allow fiber length reduction in comparison with silica fibers. The silica cladding provides high mechanical strength and protects the phosphate core from air moisture while making it easier to splice with silica fibers.
A procedure for the preparation of optically homogeneous glass for fiber preforms through sintering of coarse oxide
particles and further processing of the resultant glass, including several drawing and stacking steps, is described.
Reducing the pressure to 10<sup>-2</sup> Torr during sintering considerably reduced the amount of gas bubbles in Yb/Al-doped
silica glass and decreased the background loss to 100 dB/km after the third drawing-stacking-consolidation cycle. For
comparison, a fiber singly doped with alumina was fabricated by the same procedure as above. The level of wavelength-
independent losses in that fiber was 65 dB/km.
Prospects of fabrication of solid-core photonic bandgap fibers with a large mode area (LMA) are discussed. Properties
of solid-core photonic bandgap fibers with a small ratio of the cladding element diameter d to the distance Λ between
neighboring cladding elements are studied. The range of fiber parameters at which the fiber is single-mode over the
fundamental band gap is found.
In this work we have tested characteristics of EDFA based on a single-mode Er-doped fiber, pumped at 1480 nm by two-stage Raman fiber converter. As an active media of Raman fiber converter a single-mode fiber with phosphorus doped core was used. The conversion efficiency of Raman converter was measured to be 36%. Output power of EDFA as high as 26 dBm was achieved at wavelengths 1554 and 1582 nm corresponding to C and L-band of WDM systems.
The influence of the fluorine-containing precursor type in the MCVD process on the size of soot particles is investigated by the method of laser ultramicroscope. The results of these measurements have shown that Freon-113 decreases the content of large soot particles, while SiF<SUB>4</SUB> does not. These results suggest an explanation of the optical loss reduction in highly GeO<SUB>2</SUB>- or P<SUB>2</SUB>O<SUB>5</SUB>- doped single-mode fibers due to co-doping of the fiber core with fluorine.
Highly phosphorus doped (7 - 17 mol%) single-mode fibers for the application in Raman laser have been manufactured. It has been established that with increasing the P<SUB>2</SUB>O<SUB>5</SUB> concentration level, both optical losses and the fiber Raman gain coefficient increase. Using the fiber technology developed, the maximum efficiency of a single-cascaded Raman laser is achieved at a phosphorous pentoxide doping level of 12 - 14 mol% P<SUB>2</SUB>O<SUB>5</SUB>.
A technology has been developed for fabrication of single- mode fibers with a high level of phosphorous doping (10 - 17 mol% P<SUB>2</SUB>O<SUB>5</SUB>) in the core. Characteristics of such fibers intended for use in Raman lasers operating at 1.24 and 1.48 micrometers are investigated. A reduction of fiber drawing temperature and additional doping of the fiber core with fluorine allowed a reduction of optical losses below 1 dB/km in wavelength range 1.1 - 1.5 micrometers .