O N Egorova

Fabrication and investigation of single-mode highly phosphorus-doped fibers for Raman lasers

A technology has been developed for fabrication of single- mode fibers with a high level of phosphorous doping (10 - 17 mol% P2O5) 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 .

All-solid photonic bandgap fiber with large mode area and high order modes suppression

We present all-solid bandgap fiber design with the small ratio of cladding elements diameter to pitch (0.24), with MFD of 36 m at 1 m wavelength and higher order mode suppression caused by the propagation loss difference.

Phosphosilicate-core single-mode fibers intended for use as active medium of Raman lasers and amplifiers

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 P2O5 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% P2O5.

High-beam quality, high-efficiency laser based on fiber with heavily Yb(3+)-doped phosphate core and silica cladding.

We have fabricated and tested a composite fiber with an Yb(3+)-doped phosphate glass core and silica cladding. Oscillation with a slope efficiency of 74% was achieved using core pumping at 976 nm with fiber lengths of 48-90 mm in a simple laser configuration, where the cavity was formed by a high-reflectivity Bragg grating and the cleaved fiber end. The measured M(2) factors were as low as 1.05-1.22 even though the fiber was multimode at the lasing wavelength.

Active material for fiber core made by powder-in-tube method: subsequent homogenization by means of stack-and-draw technique

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 10-2 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.

Measuring the difference in group delays between the cores of a multicore optical fiber by means of time-domain interferometry

A way of measuring the difference in group delays between the cores of multi-core optical fiber is proposed. The method is based on a low-coherence Mach–Zehnder interferometer and a broadband radiation source. The corresponding experimental setup is constructed and a seven-core optical fiber with identical cores manufactured at the Fiber Optics Research Center, Russian Academy of Sciences, is studied.

Crosstalk in rectangular cross-section heterogeneous multicore fiber

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.

Influence of fluorine codoping on optical losses in Ge- and P-doped fibers

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 SiF4 does not. These results suggest an explanation of the optical loss reduction in highly GeO2- or P2O5- doped single-mode fibers due to co-doping of the fiber core with fluorine.

Reliability of multicore optical fibers in fiber-optic delay lines

Analytical expressions for estimating the minimum acceptable bending diameter are derived as a function of the expected service life, probability of premature fracture, and optical fiber diameter, which can be used to estimate the multicore optical fiber functionality in the particular applications.

Fiber-optic delay line using multicore fiber

A fiber-optic delay line based on a multicore optical fiber is fabricated for the first time. Due to the optical pulse sequential passage over all cores, the time delay of the optical signal of 45.0 μs is obtained at the optical fiber length of only 1300 m. The use of the seven-core optical fiber allows a sevenfold reduction in the used fiber length in comparison with single-core fibers, which is promising for developing lines with long signal delays.