This work introduces first time fabricated spun silica microstructured optical fiber (MOF) with inclusion seven GeO2-doped capillaries, placed in the central part of MOF cross-section, and induced twisting. While Part I discussed technological issues for manufacturing of described complicated twisted fiber optic structure, presented some pilot samples of described MOFs with various twisting order and measured their transmission spectra, Part II describes some results of results of experimental researches, performed for successfully manufactured twisted MOF pilot samples with typical hexagonal geometry under hole radius 4.40 μm and pitch 9.80 μm, outer “telecommunication” diameter 125 μm, and center part, formed by seven hollow GeO2-doped ring cores with inner radius 2.50 μm, pitch 8.80 μm and refractive index difference Δn=0.030 with induced twisting 130, 300 and 730 revolutions per meter. Following test series were performed: measurements of far-field laser beam profiles, some attempts of fusion splicing of typical telecommunication optical fibers and fabricated MOF with insertion loss estimation, and spectral response measurements of both single and group WDM (Wavelength Division Multiplexing)-channels of commercially available telecom WDM-system under inclusion of 2 m length MOF into various spans of short-range lab fiber optic link.
In radar systems, when solving the problem of detecting objects behind dielectrically transparent obstacles against a background of noise and interference, methods of compressing modulated UWB signals are often used. The most widespread in solving this problem are Barker codes, which are binary sequences of finite length N = 2,3,4,5,7,11,13. One of the main features of Barker codes is the equality of the amplitudes of all lateral maxima of the autocorrelation function at their minimum possible level not exceeding 1 / N. Code sequences with such properties have not been found for N< 13. Recently, the theory of quasi-orthogonal matrices has arisen and is being developed, which include the Mersenne and Raghavararo matrices. Mersenne matrices exist in all orders N = 4n-1, where n is a natural number. The indicated matrices, which are the kernel of the Hadamard matrices and generalize them, can have both cyclic and symmetric constructions. In this paper, we consider the modulation of UWB signals using the Mersenne and Raghavararo codes obtained from the rows of the corresponding quasi-orthogonal matrices. The compression characteristics of code-modulated signals in comparison with Barker codes are investigated by the method of simulation modeling. The results of evaluating the compression characteristics of the considered signals showed the advisability of using, for example, for N = 13 the Raghavararo code instead of the Barker codes. This provides greater noise immunity of UWB signals in the channels for detecting objects behind obstacles. Since, in addition to radar systems, the Barker sequence of length 11 is widely used in digital data transmission systems, the developed simulation model and the results obtained using Mersenne codes are of great theoretical and practical importance in studies of noise immunity in digital UWB data transmission channels in a complex electromagnetic environment.
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