We conducted a strain characterization experiment to detect concrete beam cracks using distributed Brillouin sensor
system. An accurate Brillouin multiple-peak fitting method is used to enhance the spatial and strain resolution. This
allows us to exactly extract the distributed strain section that is smaller than the spatial resolution of the Brillouin sensor
The effects of temperature on the Brillouin spectrum in novel carbon/polyimide coated fibers have been firstly studied.
We also firstly investigated the aging behavior for these fibers by comparing the changing of the relationship between
Brillouin frequency shift and temperature.
We monitored the distributed strain during the pipeline buckling process using distributed Brillouin sensor, which allows us to predict the buckling or crack location according to the sequence and location of the deformation for the first time using the broadening factor of Brillouin spectrum width. Two pipelines were designed and instrumented with polymer and carbon/polyimide coated fibers, and then the pipelines were subjected to internal pressure, axial tensile force and bending moment. We show that 1) the localized buckling occurred at the top, median and bottom of the pipeline, where the maximum broaden factors were obtained; 2) the deformation sequence can be measured using the nonlinearity of the broadening factor, 3) a high strength carbon/polyimide-coated fiber can detect higher stress accurately than standard telecom fibers. Our results strengthen the distributed Brillouin fiber sensor position as a nervous system to identify the potential problem in early stage for structural health monitoring.
In this letter, we put forward a new kind of polarization-maintaining index-guiding photonic crystal fiber (PM-IG-PCF).
It is made up of a solid silica core, two big circular air holes near the core and a cladding with elliptical air holes. By
making use of a full-vector finite-element method (FEM), we study the modal birefringence and polarization mode
dispersion (PMD) as a function of the normalized wavelength of fundamental modes in the PM-IG-PCF we proposed.
Numerical results show that very high modal birefringence with magnitude of order of 10<sup>-3</sup> has been obtained, which is
higher than the birefringence induced by adding two big air holes near the core or elliptical air holes in cladding
separately. Furthermore, the chromatic dispersion curves of the two orthogonal polarizations for the birefringence PCF
are presented as a function of the normalized wavelength.
Tunable photonic bandgap fibers (PBGFs) were theoretically investigated by using the vector plane-wave expansion method and the vector finite element method. The tunable PBGFs are fabricated by filling a high-index material in the air holes of index-guiding photonic crystal fibers. The wavelength dependence of leaky loss and group velocity dispersion (GVD) has been illustrated. We show the leaky loss in the tunable PBGFs can strongly depend on the refractive index of filled material due to the photonic bandgap effect. The tunable attenuator which operates at 1550 nm is designed based on this PBGFs.
Tunable photonic bandgap fibers (PBGFs) were theoretically investigated by using the vector plane-wave expansion method and the vector finite element method. The tunable PBGFs are fabricated by filling high index material in the air holes of index-guiding photonic crystal fibers. The wavelength dependence of leaky loss and group velocity dispersion (GVD) has been illustrated. We show the leaky loss in the tunable PBGFs can be strongly depended on the refractive index of filled material due to the photonic bandgap effect. The tunable attenuator which operates at 1550nm is designed based on this PBGFs.
Novel highly birefringent photonic bandgap fibers (PBGFs) are obtained by filling high index material in the air holes of total internal reflection birefringent photonic crystal fibers. The effect of filling high-index material on the transmission characteristics has been theoretically investigated. The photonic bandgap has been achieved by using the plane-wave method. Moreover, the polarization mode dispersion (PMD) has been studied by a full-vector finite-element method. Numerical results show that very high PMD with magnitude of order of 10<sup>-10</sup> has been respectively acquired, which is much higher than those of the non-filled fibers. Furthermore, strong coupling between surface modes and the fundamental modes has been found in the bandgap of the birefringent PBGFs.
In this letter, long period gratings fabricated in single-mode microstructure fibers (index-guiding MF and PBG MF) were achieved by putting periodic pressure on the cladding along the fiber length, furthermore, the characteristics of the LPGs were discussed.
Using a full-vector finite element method, the phase modal birefringence and group modal birefringence to lateral pressure alone slow axis and fast axis versus wavelength in birefringence microstructure fiber was analyzed. In the wave band of our research, 600nm-1700nm, when different direction pressure is applied, the phase modal birefringence (B) and group modal birefringence (G) have different change to wavelength in microstructure fiber. Moreover, the results reveal that the pressure sensitivity of B and G have different change to wavelength when applying different direction lateral pressure. Our research has great signification in designing microstructure fiber and using microstructure fiber in sensing field et.al., especially using in multidimensional sensor.
We present theoretical analysis of tunable bandgap guidance in virtue of bandgap theory. By means of plane-wave method a novel tunable photonic bandgap microstructure fiber (MF) was investigated by tuning the refractive index of nematic liquid crystal crystal (NLC) filled in the holes of MFs. Moreover, by using a full-vector finite-element method (FEM) with anisotropic perfectly matched layers (PMLs), the dispersion curves of NLC filled MFs have been computed with different value of the refractive index of NLC. Moreover, the leakage loss of the fundamental modes of the NLC filled MFs has been analyzed.
We present a numerical study of the guidance and amplification properties in an Er<sup>3+</sup>-doped honeycomb photonic bandgap fiber with down-doped core. Our analysis is based on a full-vector plane-wave expansion method and Runge-Kutta iterative algorithm. Overlap integrals between mode profiles and Er<sup>3+</sup>-doped region varies from 0.973 to 0.350 in guiding range of the fiber. The highly efficient amplifier can be designed by using this fiber.
A novel Moire grating in Yb<sup>3+</sup>-doped double-clad fiber is reported. It consists of two intracore Bragg reflection gratings separated by an optical phase shift; the grating was formed through double exposure phase-mask method. An Yb<sup>3+</sup>-doped double-clad fiber laser based on this grating is presented. The laser wavelengths are 1055nm and 1057nm, respectively, with less than 0.1nm line-width, over 40dB signal-to-noise ratio.