This work presents overview of technological issues concerned with drawing of twisted silica microstructured optical fibers. We present results of drawing tower modifications with developed and verified technological modes, that provide fabrication of silica microstructured optical fibers with induced chirality up to extremely high twisting order of 800 revolutions per meter (rpm). Thus, a work package using the original designer technical solutions for upgrade the adapter for supplying overpressure to the cane holes of the microstructured optical fiber (MOF) was carried out. Hence, the target increase in the twisting speed in the cane feed unit to 2000 rpm is ensured while simultaneously target overpressure feeding to the cane holes, which prevents the hole collapsing in the process of MOF drawing. The reliability of the adapter design and the high reproducibility of the specified cross section structure for the MOF at lengths of more than 50 meters with a twist period of 500 rpm have been experimentally confirmed. For the first time in the Russian Federation, prototypes of "stable" chiral MOF lengths (more than 50 m) of a different configuration with a maximum induced twisting of 500 rpm and MOFs prototypes with structure stability at lengths of less than 50 m with a strongly induced chirality of up to 790 rpm were fabricated. The geometric patterns of these fibers are also presented in this work.
We developed and characterized luminescent temperature sensors with a simple construction based on YAG : Ln3 + (Ln = Nd, Yb, Ce) nanocrystals and silica multimode optical fibers. Lanthanide-doped nanocrystals 40 to 60 nm in size were synthesized in the form of powders using the modified Pechini method. The obtained materials exhibited high sensitivity of luminescence intensity to temperature variations at wavelengths of 550 nm (YAG : Ce3 + ), 1030 nm (YAG : Yb3 + ), and 1064 nm (YAG : Nd3 + ) in the temperature range 50°C to 600°C. Additionally, we offered a method to eliminate influence of vibration on accuracy of temperature measurements by adding SiO2 sol to powders after their synthesis in sensitive elements.
The polymer-salt method was applied to synthesize nanoscale Gd2O3:Nd3+ phosphors in the form of thin films on the inner surfaces of capillaries which organize the structure of a silica hollow-core anti-resonant optical fiber. To obtain luminescing centers, the preform of a hollow-core anti-resonant optical fiber was impregnated with a homogeneous mixture of Gd(NO3)3 and NdCl3 dissolved in water and organic solvent (polyvinylpyrrolidone). This procedure was followed by a few post-processing steps, including drying of the impregnated preform in normal conditions and its thermal treatment at temperature 1000 °C. As a result, Gd2O3:Nd3+-based thin films were produced inside the capillaries. Finally, the modified preform was drawn into the hollow-core anti-resonant optical fiber of 120 μm in diameter at temperature 1850 °C. The analysis of crystallographic structure of the initial Gd2O3:Nd3+ nanopowder and the same nanophosphor inside the fabricated fiber revealed the absence of structural and phase transformations of synthesized nanocrystals with an average size 35 nm after drawing. The data on spectral-luminescent properties of the fabricated fiber confirmed the presence of Gd2O3:Nd3+ nanophosphors in silica glass with the main emission peak at wavelength 1064 nm. Presented method of modifying the structure of a hollow-core anti-resonant optical fiber allows formation of active silica layers without using technologically complicated and expensive CVD processes.
The paper describes the polymer-salt method of neodymium-doped aluminum yttrium garnet (YAG:Nd) crystals formation inside the channels of a microstructured silica fiber preform. The crystals formation was performed through the impregnation of inner surfaces of the channels by aqueous solutions of thermally decomposable salts (yttrium nitrate, aluminum nitrate, neodymium chloride) and an organic polymer with subsequent processes of drying and thermal treatment at the temperature of 1100°C. The composite structure prepared was drawn into the fiber at the temperature of 2000°C. The X-ray diffraction analysis revealed the formation of YAG:Nd crystals from 25 nm to 37 nm in size in the silica glass matrix of the fiber. Measurement of the attenuation spectral dependence confirmed the presence of optical signal absorption bands inherent to Nd3+ ions. The shape of the nanocrystals luminescence spectrum is characteristic to the YAG:Nd with a peak at the wavelength of 1064 nm.
The results of experimental study on the main technological aspects relating to a full production cycle of 50/125 μm silica multimode graded-index fibers with the central defect of the refractive index profile realized as a large dip are presented. Preform synthesis conditions for controllable implementation of the mentioned defect via MCVD method are analyzed and optimized. The effect of geometrical irregularities, induced by drawing optical fibers under the manual maintenance of the outer diameter stability, on attenuation has been explored. Applying the Weibull theory, a statistical evaluation of mechanical properties, particularly tensile strength, of the optical fibers drawn at various temperatures has been conducted.
Our research deals with studying picosecond pulse propagation from ytterbium laser through the large core multimode
microstructured fibers. Fibers with core sizes from 8 μm to 11 μm were investigated. Pumping in the normal dispersion
regime was made. Supercontinuum (SC) spectra were obtained in all the fiber samples. The main mechanism,
particularly four-wave mixing, responsible for SC generation was investigated theoretically.
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