1. Brillouin distributed optical fiber sensing technology
This paper mainly studies Brillouin optical time domain reflection (BOTDR) based on self released Brillouin scattering and BOTDA based on stimulated Brillouin scattering, which are used for continuous distributed measurement of temperature and strain.
2. Study on multi wavelength BOTDR and homodyne BOTDR
Using the homodyne BOTDR technology, we can obtain the continuous distributed measurement of temperature and strain by using multiple Brillouin scattering signals of leaf, smf28e + and other optical fibers without reference signal and Brillouin scattering spectrum scanning.
Structure diagram of multi wavelength heterodyne BOTDR system
C. Li, Y. Lu, X. Zhang and F. Wang, Electronics Letters, 48(18):1139-1141, 2012
Simultaneous measurement of temperature and strain based on zero difference BOTDR
Y. Lu, et. al, IEEE Photonics Technology Letters, 25(11): 1050-1053, 2013
In addition, the laboratory also carried out the research on the influence of extinction ratio of electro-optic modulator on the signal-to-noise ratio of BOTDR system (y. Lu, et.al (y. Yao, Y. Lu, et.al , IEEE Photonics Technology Letters, 24(15):1337-1339, In 2012, the BOTDR technology was successfully used to realize the high-resolution measurement of residual thermal strain of optical fiber in the cable (y. Lu, et.al Optical and lasers in engineering, 49 (9-10): 1111-1119, 2011), et.al , The 9th International Conference on Optical Communications and Networks, In order to shorten the measurement time of signal acquisition, the Brillouin signal obtained by BOTDR system was processed by using segmented Fourier transform (F. Wang, 2010), et.al , Measurement Science and Technology, 20(2):025202, 2009 )。
3.Research on BOTDA technology for detecting pulsed light on dark substrate
Detection of pulsed light on dark substrate
A dark substrate detection pulse light as shown in the figure is proposed for distributed sensing of BOTDA, which can effectively distinguish the tiny strain existing in the short length of the sensing fiber. The strain on two 5 cm long optical fibers with an interval of 30 cm is accurately measured in the laboratory.
The Brillouin frequency shift distribution in the fiber is measured.
F. Wang, X. Bao, L. Chen, Y. Li, J. Snoddy, and X. Zhang, Opt. Lett. 33, 2707-2709 (2008).
4.Influence and suppression of polarization correlation in sensor system
The polarization of light wave has a great influence on the optical fiber sensing based on Brillouin effect. A new method to eliminate polarization related noise in Brillouin optical fiber sensing system is developed. As shown in the figure, in order to eliminate the polarization related noise in Brillouin optical fiber sensing system, the structure similar to the Mach Zehnder interferometer is used. The polarization dependent noise is effectively eliminated by the structure indicated by the dotted line in the figure, as shown by the Brillouin spectrum distribution along the fiber。
Schematic diagram of BOTDR experimental device for eliminating polarization related noise
The Brillouin spectrum distribution along the fiber is measured. (a) The results are obtained by using the new method. (b) It is the result of direct measurement.
F. Wang, C. Li, X. Zhao, and X. Zhang, Appl. Opt. 51, 176-180 (2012).
5. Brillouin fiber laser and its application in BOTDR
Coherent detection is usually used to improve the detection signal-to-noise ratio (SNR) of the self released Brillouin scattering signal. Single frequency Brillouin fiber laser can be used to obtain low noise local oscillator with a frequency close to that of sensing fiber Brillouin stocks, single mode output and stable power. The remarkable advantage of this scheme is that it can save high power microwave frequency shift devices, and is conducive to the miniaturization and stability of the system. Besides being used in BOTDR system, Brillouin fiber laser with single mode continuous output is widely used in fiber optic gyroscope, fiber sensing and coherent optical communication system due to its extremely narrow linewidth and excellent coherence.
Structure diagram of BOTDR system using single frequency Brillouin fiber laser
