High-speed photography, spectra, and temperature of optical discharge in silica-based fibers

The dynamics of fiber fuse effect including process of bubble formation in fiber core was investigated. Bubbles in the core were observed not later than 20/spl divide/70 /spl mu/s after the plasma forepart passed. For the first time, the temperature of optical discharge was measured for a wide range of laser radiation powers. For 40-W laser power, the temperature reached 10/sup 4/ K, the velocity of discharge propagation having increased to 10 m/s.     

Spectral and polarization selective fiber-optic elements

A pair of coupled step-index waveguides is analyzed. Characteristic equations are obtained and used to evaluate the cutoff frequencies and coupling constants. Mode transformation at tapers is analyzed. The spectral properties of fused couplers and tapered filters for which cutoff frequencies of higher modes were observed are studied. A fiber polarization splitter is realized. A semiconductor laser with an external dispersive cavity based on the spectral selective coupler is designed     

Particularities of the photoluminescence spectra of Cr4+:Ca2GeO4 single crystal films

It was found that the room-temperature photoluminescence (PL) spectra of Cr⁴⁺:Ca₂GeO₄ single crystal films grown by magnetron sputtering on Ca₂GeO₄ bulk single crystal substrates exhibit a sharp emission band in the region of ～1.17 μm with satellites at ～1.21 and 1.27 μm. Particularities of the PL spectra are interpreted within the framework of a model based on the interaction between electrons of the Cr⁴⁺ center and the oscillations excited in the film.     

540 fs light pulses at 1.5 μm with variable repetition rateusing a tuneable twin guide laser and soliton compression in adispersion decreasing fiber

A novel and simple method to generate ultra short light pulses with variable repetition rate is demonstrated. A wavelength modulated tuneable twin guide laser, emitting blue-chirped light, together with pulse compression in a standard single mode fiber is used to generate light pulses of 3 ps width. Amplification and further compression in a dispersion decreasing fiber leads to Fourier transform limited pulses of 1.87 ps width or to 540 fs pulses with a small pedestal     

Anomalous dispersion in Er3+ and Yb3+-dopedfibers

In experimental and theoretical study of anomalous dispersion in Er³⁺and Er³⁺-Yb³⁺-doped fibers has been developed. Anomalous time delay caused by both absorption and emission at 1.535 μm has been theoretically calculated and experimentally measured. A pump power dependence of anomalous time delay in rare-earth-doped fibers has been theoretically calculated and experimentally investigated. It has been shown that pump power fluctuations lead to propagation time jitter in Er³⁺-doped fiber amplifiers. The pulse interaction due to refractive index change caused by gain saturation is predicted. It has been shown that for Er ³⁺-doped fibers with SiO₂-GeO₂ core composition, the anomalous dispersion per 1-dB gain is twice that of fibers with SiO₂-Al₂O₃ core, which is caused by gain curve form difference. A scheme of mutual compensation of intrinsic fiber dispersion and anomalous dispersion caused by Er³⁺ in the region 1.532-1.537 μm has been suggested     

Hydroxyl groups in phosphosilicate glass for optical fibers

To gain insight into the local environment of impurity hydroxyl groups in phosphosilicate glass and determine its signatures in the vibration spectrum, the IR absorption spectra of phosphosilicate glasses containing up to 20 mol % P₂O₅ were analyzed. The interaction of hydroxyl groups with phosphorus-containing centers was studied with the use of a cluster model and the PM3 and MNDO quantum-chemical methods. The observed changes in the OH-stretching region of the absorption spectrum were interpreted using the modeling results.     

Optimisation of two-stage Raman converter based on phosphosilicatecore fibre: modelling and experiment

Parameter optimisation of a two-stage Raman converter based on phosphosilicate-core fibre is presented. The optimal operational regime is determined and its tolerance against variations of laser parameters is examined. Results of numerical modelling are in a good agreement with experimental data