Inorganic glass is material having nanoscaled physical and chemical inhomogeneities ad initio because glass inherits
thermodynamic fluctuations of concentration, density and anisotropy of a glass forming melt. Combining light scattering
and high temperature acoustics data allows to use the effect of internal immersion for designing multicomponent glasses
with Rayleigh scattering losses lower than those of the silica glass. Non-random spatial distribution of dopants including
rare-earth (RE) ions in a glass host (doped ion segregation) causes excessive Rayleigh scattering losses and enhancement
of RE ion-ion interaction. Therefore, it opens the way to optimize operation parameters of laser and up-converting
glasses by the proper choice of glass host composition. Results of Raman scattering spectra processing and
characterization of electrooptical (EO) sensitivity of niobate glasses showed the existence of groups with stoichiometry
of the well-known EO crystals and crystal-like orderliness (crystal motifs) in the glasses as the necessary condition of
high EO sensitivity. It was found that EO sensitivity of glasses could be essentially increased by thermal treatment.
A couple of multicomponent glasses was used to produce solid hole-free photonic crystal fiber (PCF) with high contrast
of index. These glasses were a high index barium-lanthanum flint-glass (n~1.8) and a low index cron-glass (n~1.5). The
compositions of selected glasses provided the coincidence of their viscosities in the temperature range of drawing, close
thermal expansion coefficients, and chemical compatibility. To produce the PCF densely packed bundles of glass rods
(elements) of 1 mm diameter assembled in a given structures were multiply co-drawn down to 0.2-2.0 microns diameter
of a single element. This procedure allowed scaling of initial structures and resulted in two PCF structures: axially
symmetrical eight-period structure and five-period "birefringent" structure. Optical transmission of the resultant PCF
demonstrates the existence of photonic band-gaps, and intensity distribution of propagating mode corresponds to the
results of numerical simulation performed.
Novel highly concentrated Yb/Er and Nd phosphate glasses were elaborated and microchip lasers were produced. Lasing
parameters of Yb/Er and Nd phosphate glasses were studied. Novel type of radiation excited by pumping power
sufficiently high for amplification of radiation but lower than lasing threshold was observed. It was found that indicatrix
and spectrum (comb spectrum) of this radiation differed from the parameters of both luminescence and lasing radiation.
It was found that the modulated radiation emitted by the micro-chip lasers was super luminescence. Spectral separation
between adjacent lines of comb spectrum varies with radiation wavelength, length of Fabry-Perot resonator and
refractive index of amplifying medium. The phenomenon of super luminescence modulation in Fabry-Perot micro
resonator can be used for designing the simplest comb spectral channels generators for DWDM working in 0.9-1.6 &mgr;m
spectral range. 200 and 250 spectral channels were realized for Yb/Er and Nd microchip lasers, correspondingly.
Alkali phosphate, phosphate-silicate, and phosphate-germanate glasses were studied by means of high-temperature acoustics and Rayleigh-Mandelstam-Brillouin (RMBS) and Raman scattering (RS) spectroscopies. Temperature-temporal dependences of the ultrasound velocity in the glass melts were measured at temperatures up to 1550°C. From the RMBS spectra the Landau-Placzek ratio and frequency shifts were found. A theory of the fluctuations fieezing at the cooling of the glass melt was applied to separate the contributions of the frozen-in density and concentration fluctuations to the Rayleigh scattering losses. A comparison was drawn with the losses in silica glass. The RS spectra allowed the identification of the constant-stoichiometry groups. The feasibility of the system xNa2O-(40 - x)K20-30Al203-30P205 for the fabrication of low-scattering glasses was ascertained.
Minimization of Rayleigh scattering, αs, and absorption, αabs, losses in glasses for fiber drawing is considered in the study. Glasses were studied with high temperature (to 1500°C) ultrasonic acoustics, Rayleigh and Mandel'shtam-Brillouin scattering, Raman scattering (RS) and absorption spectroscopy. Contributions into αs from "frozen-in" density and concentration fluctuations were separated. The αs (multi component glass) < αs (silica glass) relationship is realized in glasses built from structural units of a single type found from RS and characterized by low glass transition temperature. Chemical inhomogeneities can be made optically invisible by means of prompt choice of glass composition. Selective entering of multi electron ions into concentration fluctuations of glass melt (doped ion segregation) causes excessive Rayleigh scattering by glass. To shift minimum αabs of low scattering glass to longer wavelengths it is necessary to dope it by randomly distributed heavy metal ions or components decreasing modifier cation-anion bond strength of a glass network.
Structure of R2O - R'2O - SiO2 - Nb2O5, R2O - R'2O - GeO2 - Nb2O5, R2O - R'2O - P2O5 - Nb2O5 (R, R' = Li, Na, K) glasses were studied by means of Raman scattering and Rayleigh and Mandel's shtam-Brillouin scattering spectroscopy. The Kerr coefficient was measured as a function of glass composition. Microinhomogeneities responsible for Rayleigh scattering losses and electro-optical properties were found on the base of light scattering spectra processing. Comparison of alkali niobate glasses with various glass formers showed that optimum combination of high Kerr coefficient and low Rayleigh scattering losses may be achieved for alkali niobate phosphate glasses.
The results of studying the electro-optical sensitivity of industrial glasses are presented, and it is shown that Kerr constant, B, of them does not exceed 10-15 m/V2. An approach to the choice of compositions of the glasses of high Kerr sensitivity is developed, and experimental sodium- niobium-silicate glasses with B > 10-14 m/V2 have been designed and formed. The approach is based on the hypothesis of 'crystalline motifs' (structural inhomogenities responsible for electro-optical sensitivity of the glasses), which are the ordered regions (several coordination spheres) with the crystal-like structure. When heat-treated the designed glasses crystallize, with the phase precipitated being NaNbO3 microcrystals. Temporal-thermal conditions of the glass crystallization to form a transparent glass-ceramics with B approximately equal 10-12 m/V2 have been found. It has been also shown that such glass-ceramics can be produced by high-temperature alkaline ion exchange. A low- temperature silver ion exchange in the designed glasses and glass-ceramics has been studied and optical waveguides supporting from 1 to 50 modes have been formed. In these waveguides the index variation equal to 0.15 is achieved.
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