Streszczenie: W artykule przedstawiono wyniki badań eksperymentalnych i symulacji wpływu gradientu odkształcenia siatki Bragga o stałym okresie na jej charakterystyki widmowe: pasmo 3 decybelowe i współczynnik odbicia mocy. Zakres zmian gradientu odkształcenia wynosił od 0 do š27 žε/mm. Wyniki pomiarów wskazują na liniową zależność pasma 3 dB siatki od stałego gradientu odkształcenia oraz brak jego wpływu na współczynnik odbicia mocy siatki w badanym zakresie jego zmian. Wyniki tych badań mogą być przydatne przy konstrukcji czujników wielkości mechanicznych z siatkami Bragga, w których elementem sprężystym jest belka zginana oraz w pomiarach odkształceń.
Abstract: Experimental and simulation results of the influence of the strain gradient of a uniform fiber Bragg grating on its spectral characteristics, the 3-dB bandwidth and reflectivity, are presented in the paper. For experiments a 10 mm long grating embedded in a bended cantilever (Fig. 1) was used. The strain and the strain gradient of the cantilever were caused by a concentrated force acting on the cantilever free end. A change of the kind of strain (stretching or compression) and the strain gradient sign was achieved by reversing the cantilever in the holder. The range of the strain gradient equals 0š27 žε/mm. The measurements were taken in a setup shown in Fig. 2. Using the transfer matrix method derived from the coupled mode theory, the changes of the grating reflected spectrum caused by the strain and the strain gradient in it were simulated [5]. The obtained results of measurements and simulations show that increase in the strain gradient causes increase in the 3-dB bandwidth of the grating reflected beam both for a positive and negative strain gradient (Figs. 3-5). The dependence of the 3-dB bandwidth on the strain gradient is linear and symmetric with respected to the y-axis. The measurement results confirm this feature in the range š 8,5 žε/mm. Outside this range, increase in the 3-dB bandwidth for a negative strain gradient is smaller than for a positive one. For the investigated range of the grating strain gradient, its influence on the grating reflectivity was not observed (Fig. 6).This last feature is important in detection of the grating signals by means of optical wavelength discriminators.
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measurements and simulations. Experimental Mechanics, Vol. 41, no 1, 2001, pp. 19-28.
[4] Dong X., Gaun Bo., Yuan S., Tam H.: Strain gradient chirp of uniform fiiber Bragg grating without shift of central Bragg wave-length. Optics Communications, 202, 2002, pp. 91-95.
[5] Othonos A., Kalli K.: Fiber Bragg Grating Fundamentals and Applications in Telecommunications and Sensing, Artech House, Boston London 1999.
[6] Timoshenko S. P., Gere J. M.: Mechanics of materials. Von N. Reinhold Company, New York 1972.
[7] Kashyap R.: Fiber Bragg Grating. Academic Press, San Diego 1999. 
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