The purpose of conventional techniques for multiplexing fiber Bragg gratings (FBGs) is that each FBG has its own wavelength or unique intensity of reflected light. The cost pf per channel is at least of a few hundred dollars. All these limit the FBG points increasing at fiber measuring system. Based on improved Fast-ICA and self-adapting, this paper focuses on the separation of two same wavelength FBGs mixing model caused by temperature and vibration. Simulation experiment is carried out based on the initial wavelengths of two FBGs are both 1550.515nm and the temperature fluctuation range is 0-0.5°C and amplitude and frequency of exterior vibration are 0.01nm and 10Hz. Simulation data show that the separation steps consume 1.3884s and mean and mean square of absolute errors between the original and separated signals are 8.11·10<sup>-9</sup>, -5.83·10<sup>-12</sup>, and 2.57·10<sup>-6</sup>, 2.42·10<sup>-9</sup>, correspondingly. Therefore, through using this separation method, two same wavelength FBGs could achieve simultaneously measurement of temperature and vibration at one channel. This could double measuring points of fiber detection system, effectively.
High-temperature experiments for electroless Cu-plating Fiber Bragg Grating (FBG) indicate that Cu-plating FBG can
measure high-temperature up to (even beyond) 300°C and it has high linearity, accuracy and repeatability. We can
control Cu-plating FBG’s temperature sensitivity by controlling plating layer’s thickness. Temperature sensitivity of
FBG with Cu-plating can be improved by more than three times with no less than 300μmthick coating by electroless
and electrical Cu-plating. Such FBG can be soldered onto metal structures to get good bonding with the structure. As a
result, such fiber sensors can get good protection, and high-temperature monitoring of smart structure is obtained.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
Optical fiber grating (FBG) has been widely used in the measurement of parameters such as temperature and strain. However, FBG is too slim to broken, whose outside protective layer tends to shedding easily, and it is also hard to change the temperature and strain sensitivity. In order to overcome the above disadvantages and to further expand the application range of FBG, this paper improves the technology of fiber grating metal film plating process firstly. It adopts a compositive method including chemical plating and electroplating to gild FBG, copper FBG and galvanize FBG, which all get good metal coating. Then, the temperature and strain sensing properties of metalized FBG is studied in detail. Multiple metal coating FBGs were put in high-low temperature test-box together, and then the test-box worked continuously at the temperature range of 0°C～95°C. After several experiments, it concludes that metal plating enhances the temperature sensitivity of fiber grating, and the one with galvanization has the highest temperature sensitivity of 0.0235. At last, FBGs with various cladding were pasted on carbon fiber cantilever beam respectively and the pressure on the top of the cantilever increased gradually. The experimental results show that wavelength of fiber grating shift toward the long wavelength with the increase of the pressure, and the one with galvanization has the maximum strain sensitivity which has minimal impact on fiber properties.
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.
To increase the multiplying density of FBG sensors, a novel FBG sensing network using CDM + SDM by coding
measuring points directly is proposed, which increases the multiplying density greatly and is easy to implement in
engineering for its simple structure. Simulation of an example using (25,3,1)-OOC code indicates that although the
system's multiplying density increased greatly, its measuring precision decreased.
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.
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.
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.