response and gain [see gain in Fig. 2(a), the smaller corresponds to F5 that has less fiber length]. To prove the tailoring capacity of the device, the spectral response from the first four fibers is converted in a ''W like shape'' by a proper tuning of the temperature. In Figure 2(b), the Brillouin spectra from each fiber and their superposition response (continuous line) when F1 and F2 are at 58 C and F3-F5 at 20 C are plotted. The first two BFS peaks, i.e., F1 and F2 are moved to the right and hence peaks m B2 and m B3 become one, which is broader than the original peak F3. The resultant second peak is twice the bandwidth of peak 2 or 3 (30 MHz at 3 dB). The reject bands are placed at 10.756 GHz and 10.834 GHz, respectively, from the pump wave. A third reject band, that is the gap between m B4 and m B5 , has 170 MHz of bandwidth and centre at 10.965 GHz from the pump [ Fig. 2By varying the temperature in the SBAD, the reject band or the bandwidth is tuned, then a specific behavior in the spectral response of the device is obtained. The Brillouin gain distribution from F1 to F4 at temperature variations between 54 C and 64 C is depicted in Figure 3. Figure 4 shows the bandwidth value between m B2 and m B3 as a function of the increment in temperature that is similar to the dependence of BFS on the temperature [1]. CONCLUSIONSAn optical active device based on the composition of the Brillouin gain spectral response is presented. It is made by the proper connection of serial and parallel pieces of fiber. The fibers have different lengths, optical and geometrical characteristics, in addition to the tuning effect of the temperature that confers a great flexibility and several degrees of freedom to reach the required Brillouin spectral response. We have developed devices with Brillouin spectrum responses that can be used as narrow optical filters, e.g., Brillouin optical amplifiers and narrow comb lasers that are the more significance. The proposed method can be a powerful tool to use in all-optical devices to handle optical signals in optical communications and signal processing.ABSTRACT: In this article, antennas over metamaterials substrates are investigated with the radiating Q factor determined by using a time-domain method. The main objective is to illustrate the electromagnetic behavior of this kind of complex structure by calculating its energy budget (stored and radiated energies). An example of a patch antenna using such materials is analyzed and experimental results are presented.
A single-mode fiber (SMF) acousto-optic tunable filter (AOTF) with a tuning range of more than 300 nm is demonstrated. The SMF used in the experiment has a ring of symmetric holes within the cladding, which causes a larger mode-index difference between the first and the second higher-order antisymmetric modes than those of a conventional SMF. As a result, the difference in beatlengths between the core mode and the higher-order modes is highly increased, which makes it possible for the SMF AOTF to exhibit a single resonance peak in the transmission spectrum over the wavelength range of 1.3-1.6 μm for given acoustic frequencies of 3.1-3.8 MHz.
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