Stimulated Brillouin scattering in optical fibers is described by a theoretical model and numerical analysis. The results showed that, for an optical fiber pumped by a laser beam with ns-order-pulse width and kW-order...Stimulated Brillouin scattering in optical fibers is described by a theoretical model and numerical analysis. The results showed that, for an optical fiber pumped by a laser beam with ns-order-pulse width and kW-order peak-power, SBS reflectivity tends to saturate when the fiber length exceeds a limit, named 'effective fiber length'. Using small core-diameter and long enough fiber, the SBS reflectivity level could be raised but is limited by optical damage of the entrance surface of the fiber. Therefore, just a small dynamic range can be obtained.展开更多
In this paper,we propose a method to realize microwave photonic filter(MPF) with complex coefficient,whose central frequency f 0 and 3 dB bandwidth are tunable.The complex coefficient is realized by multi-wavelength o...In this paper,we propose a method to realize microwave photonic filter(MPF) with complex coefficient,whose central frequency f 0 and 3 dB bandwidth are tunable.The complex coefficient is realized by multi-wavelength optical source and stimulated Brillouin scattering(SBS).The central frequency of the filter is tuned by adjusting the phase shift caused by SBS without changing its frequency response.The frequency selectivity of filter can be improved through increasing the bandwidth of broadband optical source(BOS) or decreasing wavelength separation to increase the taps of MPF.The mainlobeto-sidelobe suppression ratio(MSSR) of the filter is affected by the weight of each tap.When the length of fiber is 0.5544 m in birefringence fiber loop mirror(FLM),the MSSR is improved by 18.55 dB compared with that without the weight controlling.展开更多
In this paper, we have designed and proofed a widely tunable microwave photonic filter (MPF) on the basis of self-adaptive optical carrier regeneration method through stimulated Brillouin scattering (SBS) amplificati...In this paper, we have designed and proofed a widely tunable microwave photonic filter (MPF) on the basis of self-adaptive optical carrier regeneration method through stimulated Brillouin scattering (SBS) amplification. The MPF system features with a single microwave passband as the result of the processed signal sideband beating with the regenerated optical carrier. Since the Brillouin-laser optical carrier and the SBS amplification are generated from one laser source, the optical carrier regeneration process of the proposed MPF is self- adaptive and carrier-frequency independent. Moreover, by simply varying the wavelength spacing between the optical carrier and the optical filter, the central passband of the MPF can be continuously tuned from 6 to 32 GHz, which is limited by the bandwidth of the modulator and the photodetector. The 3 dB bandwidth and the out-of-band suppression ratio of the MPF can reach 640 MHz and 21 dB, respectively.展开更多
This paper investigates the application of distributed optical fiber strain sensors to civil engineering structures, because no other tool can satisfactorily detect the location of the unpredictable phenomenon. In fac...This paper investigates the application of distributed optical fiber strain sensors to civil engineering structures, because no other tool can satisfactorily detect the location of the unpredictable phenomenon. In fact, the locations of cracks in the concrete structure are unknown a priori; therefore, a fully distributed sensor is necessary to detect them. The Brillouin optical correlation domain analysis （BOCDA）, which offers high spatial resolution by using stimulated Brillouin scattering along the whole length of the optical fiber, is used in a wide range of civil engineering applications, and the same has undergone significant development over the last decade. In this paper, it is demonstrated how a BOCDA-based strain sensor can be employed to monitor cracks in concrete. Crack monitoring on the surface of the concrete member provides useful information for evaluating stiffness and durability of the structure, particularly for early detection of tiny cracks, which is essential for preventing crack growth and dispersion. The crack-induced strain distribution was analytically investigated, and it was proved that BOCDA can identify even a small crack before its visual recognition by a beam test. Moreover, periodical crack monitoring was successfully executed on a pedestrian deck for five years.展开更多
文摘Stimulated Brillouin scattering in optical fibers is described by a theoretical model and numerical analysis. The results showed that, for an optical fiber pumped by a laser beam with ns-order-pulse width and kW-order peak-power, SBS reflectivity tends to saturate when the fiber length exceeds a limit, named 'effective fiber length'. Using small core-diameter and long enough fiber, the SBS reflectivity level could be raised but is limited by optical damage of the entrance surface of the fiber. Therefore, just a small dynamic range can be obtained.
基金supported by the National Natural Science Foundation of China (No.60808004)
文摘In this paper,we propose a method to realize microwave photonic filter(MPF) with complex coefficient,whose central frequency f 0 and 3 dB bandwidth are tunable.The complex coefficient is realized by multi-wavelength optical source and stimulated Brillouin scattering(SBS).The central frequency of the filter is tuned by adjusting the phase shift caused by SBS without changing its frequency response.The frequency selectivity of filter can be improved through increasing the bandwidth of broadband optical source(BOS) or decreasing wavelength separation to increase the taps of MPF.The mainlobeto-sidelobe suppression ratio(MSSR) of the filter is affected by the weight of each tap.When the length of fiber is 0.5544 m in birefringence fiber loop mirror(FLM),the MSSR is improved by 18.55 dB compared with that without the weight controlling.
基金supported by the National Natural Science Foundation of China (Grant Nos. 61501422 & 61377071)the Equipment Development Project of Chinese Academy of Sciences (Grant No. YZ201201)
文摘In this paper, we have designed and proofed a widely tunable microwave photonic filter (MPF) on the basis of self-adaptive optical carrier regeneration method through stimulated Brillouin scattering (SBS) amplification. The MPF system features with a single microwave passband as the result of the processed signal sideband beating with the regenerated optical carrier. Since the Brillouin-laser optical carrier and the SBS amplification are generated from one laser source, the optical carrier regeneration process of the proposed MPF is self- adaptive and carrier-frequency independent. Moreover, by simply varying the wavelength spacing between the optical carrier and the optical filter, the central passband of the MPF can be continuously tuned from 6 to 32 GHz, which is limited by the bandwidth of the modulator and the photodetector. The 3 dB bandwidth and the out-of-band suppression ratio of the MPF can reach 640 MHz and 21 dB, respectively.
文摘This paper investigates the application of distributed optical fiber strain sensors to civil engineering structures, because no other tool can satisfactorily detect the location of the unpredictable phenomenon. In fact, the locations of cracks in the concrete structure are unknown a priori; therefore, a fully distributed sensor is necessary to detect them. The Brillouin optical correlation domain analysis （BOCDA）, which offers high spatial resolution by using stimulated Brillouin scattering along the whole length of the optical fiber, is used in a wide range of civil engineering applications, and the same has undergone significant development over the last decade. In this paper, it is demonstrated how a BOCDA-based strain sensor can be employed to monitor cracks in concrete. Crack monitoring on the surface of the concrete member provides useful information for evaluating stiffness and durability of the structure, particularly for early detection of tiny cracks, which is essential for preventing crack growth and dispersion. The crack-induced strain distribution was analytically investigated, and it was proved that BOCDA can identify even a small crack before its visual recognition by a beam test. Moreover, periodical crack monitoring was successfully executed on a pedestrian deck for five years.
