V. V. Dorofeev

Widely tunable mid-infrared fiber laser source based on soliton self-frequency shift in microstructured tellurite fiber.

A turnkey fiber laser source generating high-quality pulses with a spectral sech shape and Fourier transform-limited duration of order 100 fs widely tunable in the 1.6-2.65 μm range is presented. It is based on Raman soliton self-frequency shifting in the suspended-core microstructured TeO2-WO3-La2O3 glass fiber pumped by a hybrid Er/Tm fiber system. Detailed experimental and theoretical studies, which are in a very good agreement, of nonlinear pulse dynamics in the tellurite fiber with carefully measured and calculated parameters are reported. A quantitatively verified numerical model is used to show Raman soliton shift in the range well beyond 3 μm for increased pump energy.

Toward a mid-infrared femtosecond laser system with suspended-core tungstate–tellurite glass fibers

A simple design of a fiber laser system for generating high-quality pulses with a duration of order 100 fs with ultrabroad wavelength tunability in the 2-5 μm range is discussed. This design incorporates conventional fs near-IR lasers and specially developed tungstate-tellurite fibers with two zero-dispersion wavelengths (ZDW) and relies on nonlinear wavelength conversion via either soliton self-frequency shift (SSFS) or red-shifted dispersive wave (DW) generation. The fiber parameters needed for such optical conversion have been scanned numerically and showed a possibility of SSFS beyond 4 μm and of DW generation beyond 5 μm. We have also studied and prepared tungstate-tellurite glasses and preforms that are highly stable against crystallization, exhibit extremely low level of hydroxyl groups absorption, and from which the suspended-core two-ZDW fibers can be manufactured.

Low-loss, high-purity (TeO2)0.75(WO3)0.25 glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO2)0.75(WO3)0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 102 cm−3, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm−1. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.

Extinction coefficient of Ni2+ in (TeO2)0.78(WO3)0.22 glass

The absorption spectra of (TeO2)0.78(WO3)0.22 glasses containing 0.01–1.0 wt % NiO have been measured at wavelengths from 450 to 2700 nm, and the spectral dependence of the extinction coefficient of Ni2+ in the glasses has been obtained. In the absorption bands centered at 810 and 1320 nm, the extinction coefficient is 20.2 ± 0.8 cm−1 (870 ± 35 dB/(km ppmw)). According to the spectral range of its absorption and its extinction coefficient, nickel is a strongly absorbing impurity in tellurite glasses. The present results can be used to formulate sound nickel concentration limits in tellurite glasses for fiber-optic applications.

Effect of full compensation of thermally induced depolarization in two nonidentical laser elements.

Thermally induced depolarization of radiation introduced by a system of two optical elements separated by a quartz rotator has been analyzed. The conditions of full compensation of thermally induced depolarization for two nonidentical optical elements have been found. The model experiment has demonstrated that full compensation in two optical elements of different materials is possible without a quartz rotator between them.

A mathematical model for analysis of sequentially coupled crystallization–melting differential scanning calorimetry peaks and the use of the model for assessing the crystallization resistance of tellurite glasses

Differential scanning calorimetry (DSC) characterization of tellurite glasses doped with lanthanum oxide, which improves their crystallization resistance, has revealed a phase transformation specific to such glasses, in which partial crystallization of a sample is followed by melting of the crystals formed. The experimentally observed dependence of the decrease of crystallization–melting peaks across a series of disperse samples of (TeO2)0.72(WO3)0.24(La2O3)0.04 glass with increasing particle size upon extrapolation to the size of a bulk sample has been used to assess the crystallization resistance of tellurite glasses for optical applications. The assessment technique comprises DSC characterization of particle-size-classified glass samples and the use of a mathematical model for obtaining the degree of crystallization as a function of temperature and time, α(T, t) through analysis of nonisothermal DSC peaks representing a partial glass crystallization process passing into melting. The crystallization resistance of glass is estimated by extrapolating the maximum α values as a function of particle size to a preform size. Tested for (TeO2)0.72(WO3)0.24(La2O3)0.04 glass, the technique offers the possibility of selecting preforms for producing fibers from compositionally new, chemically pure tellurite glasses at a given phase purity level.

Tungstate-tellurite glass fibers for spectral region up to 3 µm

Optical fibers were produced from high-purity TeO2-WO3-La2O3-(Bi2O3) glasses. Total loss was less than 0.5 dB/m at 1.2-2.8 μm and about 2 dB/m at maximum of OH-groups absorption at 3 μm with further sharp increase.

Thermodynamic properties of (TeO2)0.95 − n − z (ZnO) z (Na2O) n (Bi2O3)0.05 glasses

AbstractThe heat capacity (Cp0) of the tellurite glasses

Development of Er^3+-doped high-purity tellurite glass fibers for gain-switched laser operation at 27 μm

\begin{gathered} (TeO_2 )_{0.70} (ZnO)_{0.15} (Na_2 O)_{0.10} (Bi_2 O_3 )_{0.05} (I), \hfill \\ (TeO_2 )_{0.75} (ZnO)_{0.10} (Na_2 O)_{0.10} (Bi_2 O_3 )_{0.05} (II),and \hfill \\ (TeO_2 )_{0.75} (ZnO)_{0.15} (Na_2 O)_{0.05} (Bi_2 O_3 )_{0.05} (III) \hfill \\ \end{gathered}

Fabrication of glasses in the TeO2-WO3 system using plasma chemical oxidation of tellurium and tungsten chlorides

has been measured in the temperature range 255–750 K using a differential scanning calorimeter (glasses I–III) and in the range 208–325 K using an adiabatic calorimeter (glass II). We have determined the temperature ranges of the glass transition, evaluated the thermodynamic characteristics of the glass transition and glassy state, and estimated the crystallization onset temperatures. Using the experimental data and a statistical model approach, we have calculated the standard thermodynamic functions for glassy and “supercooled liquid” states in the temperature range 0–740 K: heat capacity Cp0(T), enthalpy H0(T) − H0(0), entropy S0(T) − S0(0), and Gibbs function G0(T) − G0(0).