Yu P. Yatsenko

PHOTOINDUCED SECOND-HARMONIC GENERATION IN FIBERS DOPED WITH RARE-EARTH IONS

Photoinduced second-harmonic generation in silica fibers doped with Er(3+), Sm(3+), and Tb(3+) has been investigated. Er(3+)-doped fibers have been found to tune a chi((2)) grating easily to the mode structure of the laser radiation, whereas Sm(3+)-doped fibers have been found to possess the greatest resistance to chi((2)) grating erasure by radiation at 532 nm. From the beginning of the preparation processes, the third harmonic at 355 nm is registered in all the fibers.

4.4-μm Raman laser based on hollow-core silica fibre

A Raman laser with a wavelength exceeding 4 μm is designed for the first time. Using a revolver silica fibre with a hollow core filled with molecular hydrogen (1H2) as an active medium, we have obtained SRS lasing at a wavelength of 4.4 μm under pumping by a pulsed erbium fibre laser (λ = 1.56 μm, τ = 2 ns). The SRS conversion quantum efficiency reaches 15 %, and the maximum output peak power at a wavelength of 4.4 μm is 0.6 kW.

Multiband supercontinuum generation in an air-core revolver fibre

Multiband supercontinuum generation in an air-core revolver fibre having a large number of transmission bands in a wide spectral range has been studied experimentally and theoretically for the first time. The fibre fabricated by us possesses unique dispersion and guidance characteristics for radiation transfer from one band to another despite the high losses at the band boundaries. In our experiments, launching 205-fs laser pulses of 110 μJ energy at 1028 nm into the fibre we have obtained a supercontinuum spanning the spectral range from 415 to 1593 nm, with 11 transmission bands. Numerical simulation suggests that, in the case of single-mode propagation of pulses with such energy in the fibre, the supercontinuum may span 14 transmission bands and have a spectral width above three octaves, with a long-wavelength edge at 4200 nm.

Propagation of femtosecond pulses in a hollow-core revolver fibre

We have studied for the first time the propagation of femtosecond pulses through an optical fibre with an air-filled hollow core and a cladding in the form of one ring of noncontacting cylindrical capillaries for high-power radiation transmission in the 1.55-μm telecom range. Numerical analysis results demonstrate that the parameters of the fibre enable radiation transmission in the form of megawatt-power Raman solitons through up to a 25-m length of the fibre and tuning of the emission wavelength over 130 nm. We have experimentally demonstrated femtosecond pulse transmission through fibres up to 5 m in length in the linear propagation regime, without distortions of the pulse spectrum, with a dispersion-induced temporal pulse broadening within 20%.

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.

Dispersion and guidance characteristics of microstructured 68TeO{sub 2} - 22WO{sub 3} - 8La{sub 2}O{sub 3} - 2Bi{sub 2}O{sub 3} glass fibres for supercontinuum generation

We report the preparation of a high-purity optical-quality four-component glass of composition 68TeO2 — 22WO3 — 8La2O3 — 2Bi2O3, containing (2.7±0.5)×10-5 mol % OH groups. Its refractive index has been determined in the range 0.9 — 5.45 μm using interference refractometry. The data are used to assess the dispersion and guidance characteristics of microstructured optical fibres potentially attractive for supercontinuum generation in the range 1 — 5 μm