An acoustic emission (AE) linear location system is proposed, which employs fiber Bragg gratings (FBGs) as AE sensors. It is demonstrated that the FBG wavelength can be modulated as static case when the grating length is much shorter than the AE wavelength. In addition, an improved AE location method based on Gabor wavelet transform (WT) and threshold analysis is represented. The method is testified through AE linear location experiments based on a tunable narrow-band laser interrogation system using ultra-short FBG sensors as AE sensors. Results of the experiments show that 86% of the linear location errors are less than 10mm.
A multi-channel tunable mechanically induced long-period fiber gratings (LPFGs) scheme is presented, which can
induce several LPFGs with different resonance wavelengths simultaneously. LPFGs spectra characteristics are simulated
to find the influence of these parameters such as grating length, tilt angle and the pressure on the fiber. The simulation
results show that the transmission loss peak mainly depends on both the grating length and the pressure, while tilt angle
factor dominates the resonant wavelength. The infuence of the pressure and tilt angles on the transmission spectra is
experimentally studied. This multi-channel LPFGs module will have great potential applications in the fiber sensing field
and flexible filter design region.
Symmetrical apodization technique of the chirped fiber Bragg grating has the advantages of suppressing the sidelobes of
reflection spectra and smoothing the curves of group delay. However, it shortens the bandwidth of the reflection
spectrum markedly. Compared with symmetrical apodization method, the asymmetric method can increase the 3dB
bandwidth by 64.08% without the change of group delay curves. The apodization simulation is implemented by using a
rised cosine function with different apodization length ratios at both ends of the grating. There is a compromise between
the bandwidth and the group delay ripple. The result shows that the grating with 30% apodization at the long wavelength
end and 20% apodization at the short wavelength side can improve the reflection bandwidth effectively and depress the
group delay ripple within the range of ±2 ps.
The distributed optical fiber temperature measurement system (DTS) is a kind of sensing system, which is applied to the
real-time measurement of the temperature field in space. It is widely used in monitoring of production process: fire alarm
of coal mine and fuel depots, heat detection and temperature monitor of underground cable, seepage and leakage of dam.
Through analyzing temperature effect of optical fiber Raman backscattering theoretically, a distributed temperature
sensor based on single-mode fiber was designed, which overcame the inadequacies of multimode fiber. The narrow pulse
width laser, excellent InGaAS PIN, low noise precision difet operational amplifier and high speed data acquisition card
in order to improve the stability of this system were selected. The demodulation method based on ratio of Anti-Stokes
and Stokes Raman backscattering intensity was adopted. Both hardware composition and software implementation of the
system were introduced in detail. It is proved that its distinguishing ability of temperature and space are 1 m and 2 m,
respectively. The system response time is about 180 s, with a sensing range of 5 km and the temperature measurement
range 0~100 °C.