The complexity and high cost of multiplexing optical fiber sensors is still the main limitation for the widespread introduction of sensory systems, both distributed and quasi-distributed, and point-like. The article proposes a new multiplexing method that takes advantage of both broadband and two-frequency radio-photon multiplexing systems. The simplest broadband radiator is taken from the first, but a complicated and expensive system of spectrometry is not used to determine the central wavelength of fiber Bragg gratings. From the second, a recording system is used at the beat frequency between two components, but an expensive system for generating two- and polyharmonic probing systems is not used. The multiplexing parameter is determined by the frequency of separation between the transparency windows of a fiber Bragg grating, for example, with two phase π-shifts, which differs by a certain value for each of the sensors. The mechanism of modeling of gratings of the specified type is given, in principle the possibility of multiplexing of various number of sensors is shown. When using sensor networks built on the basis of passive optical, the number of multiplexed sensors can reach 256, with all sensors having the same Bragg wave of the wave, and can be combined into tree, bus and other topologies.
Keywords: fiber Bragg grating, phase inhomogeneity, fiber optic sensor, multiplexing, transparency window, frequency difference between transparency windows, beat frequency
Gas-powder dynamics within the off-axis nozzle of the Precitec YC52 laser cladding head (Germany) has been studied using the original Tepler shadow setup, the high-speed tracing system and the laser Doppler anemometer. The length of the laminar part of the gas-powder flow has been optimized for variety of the transport and shielding gas flow, as well as the diameter of the orifice of cyclone. Powder jet at the nozzle’s outlet follows the carrier gas flow structure. In case of 4 mm nozzle’s diameter, the powder stream separates into two stable vortex structures near the surface of the substrate, causing significant losses of powder particles (about 2/3 of the total powder mass) within the melting zone, which finally reduces the efficiency of the deposition process and the powder utilization. Practical recommendations on the application of the optical diagnostic to optimize gas-powder jets for laser cladding are provided.
Keywords: laser powder cladding, shadow method, off-axis nozzle, tracing, laser Doppler anemometry, gas-powder flow optimization
Laser tracking locators have certain drawbacks, among which there is a strong influence of the atmosphere on their energy and precision parameters, the process of aiming a narrow beam at the object, etc. High requirements for locators (the error of measuring the range to a few centimeters) lead to the need to take into account the state of the atmosphere on the route for application Corrections in the measurements. In particular, the phenomenon of refraction leads to a significant distortion of the signal. To reduce the error of distance measurements it is advisable to use methods to compensate for the effect of refraction or to take it into account and use the correction coefficients. The article shows that the effective solution to this problem in the absence of the possibility of obtaining operational and accurate information about meteorological parameters is the use of parallel laser probing of the atmosphere. More promising in this case is the use of laser methods for controlling atmospheric parameters, which we described and experimentally investigated at the Chauda, Feodosiya, and the Republic of Crimea provinces. The obtained atmospheric data were used to create a mobile laser-television locator for external-trajectory measurements of the descent of the aeroelastic systems "Kafa" and were installed both on the ground and on an air balloon. The trajectories of the descent of balloons and cargo parachute systems were studied.
Keywords: Laser tracking locator, ranging channel, atmospheric effect, refraction, model compensation method, laser probing
Refraction has a strong influence on the accuracy parameters of the range-finding tract of laser tracking locators and the process of directing a narrow laser beam onto the object. High requirements for locators (the error of measuring the range to a few dozen centimeters) lead to the need to take refraction into account for making corrections to the measurements. Significant distortion of the signal leads not only to the phenomenon of static refraction, but also dynamic. To reduce the error of distance measurements it is advisable to use methods to compensate for the effect of static refraction or to take it into account and use the correction coefficients. The article shows that the most effective solution to the problem of refraction in the presence of a dynamic component is also the use of parallel laser probing of the atmosphere, but it must be carried out at two different wavelengths. In this case, the main method of calculating the correction factors is the dispersion method, which makes it possible to reduce the relative measurement error to 106. The use of laser methods for controlling atmospheric parameters, including two-wave and two-frequency ones, was described by us and experimentally investigated at the Chauda, Feodosiya, and the Republic of Crimea fires on YAG: Nb3 + IZ-25 lasers and continuous lasers . The obtained atmospheric data on the LT-5Z laser were used to create a mobile laser-television locator for external-trajectory measurements of the descent of the aerial systems "Kafa +" and were installed both on the ground and on an air balloon. The flight trajectories of balloons and the descent of cargo parachute systems were studied.
Keywords: Laser tracking locator, ranging channel, atmospheric effect, static refraction, dynamic refraction, dispersion compensation method, laser two-wave probing of the atmosphere
In the article managed photon pairs generation methods in lightguides with actively formed dispersion for producing a single-photon light state are discussed. Generation principle is based on of spontaneous parametric scattering or spontaneous fourwave mixing. To get the factored state, i.e. spectral and spatial correlations between daughter photons are eliminated, the usage of photonic crystal fiber, that allow to form complex frequency dispersion profiles by changing the fiber structure, is analyzed.
Keywords: photonic-crystal fiber, quantum communications, femtosecond laser, actively formed dispersion, photon pairs, single-photon states
Modern sources based on the usage of spontaneous four-wave mixing in photonic-crystal fibers generate photon pairs in wide wavelength range. Microstructured fibers allow actively managing frequency dispersion profile. In the design of different types of photonic-crystal fibers is necessary to research the influence of microstructure on fibers properties. Nowadays one of the most perspective solutions is numerical and program modeling. Paper presents modeling of photonic-crystal fiber structures to find optimal parameters of the nonlinear medium.
Keywords: photonic-crystal fiber, modeling, photon pairs, single-photon states, spontaneous four-wave mixing