Author details

to the frequency difference between each line and the pump frequency, the pump pulse shapes the amplitude of each spectral comb line via the SBS interaction simultaneously. The total measurement time, including the necessary 100 acquisitions for the SNR improvement, results in only 10 ms [83]. Furthermore, the experimental results in Figure 21 confirm its equivalence to a conventional BOTDA regarding the temperature and strain measurement. However, the main disadvantage of this technique is the special requirement of the DOFC, which is generally not

The linear fitting of (a) temperature and (b) strain measurement with conventional BOTDA and DOFC-

**(b)**

**10.84 10.85 10.86 10.87 10.88**

**DOFC-BOTDA Conventional BOTDA**

**Frequency (GHz)**

In this chapter, the basics of SBS and its application for distributed sensing have been reviewed. The overview has started with an introduction of SBS together with its physical origin and applications due to inherent, striking advantages in a variety of fields such as slow light, optical and microwave photonic filters, and many more. Among all these exciting applications, distributed temperature and strain sensing is

The enhanced SNR and the moderate resolution are the superiority of distributed Brillouin sensors to the traditional distributed and point sensors in long-range sensing. However, conventional BOTDA sensors are limited by MI and NLE. The origins, as well as methods for the mitigation of MI and NLE, have been presented and discussed in detail. Thus, with these new methods, much longer sensing ranges

Besides the sensing range, methods to enhance the spatial resolution and the speed of the measurement have also been reviewed and discussed. Nowadays, distributed Brillouin fiber sensors can have a resolution in the centimeter range, or even below and act like thousands or millions of point sensors. At the same time, novel ideas such as multi-tone pumps have successfully shortened the measurement time in distributed SBS sensors from several minutes down to 10 ms. Due to the fruitful proof-of-concept results, some of the state-of-the-art techniques discussed

Cheng Feng wishes to acknowledge the financial support from German Research Foundation (DFG SCHN 716/13-1) and Niedersächsisches Vorab (NL—4 Project

in this chapter have already been applied in some BOTDA prototypes.

so simple to achieve.

**10.84 10.85 10.86 10.87 10.88 10.89**

**DOFC-BOTDA Conventional BOTDA**

**Frequency (GHz)**

**<sup>900</sup> (a)**

Fiber Optic Sensing - Principle, Measurement and Applications

one of the most prominent.

became possible.

Acknowledgements

78

5. Summary

Figure 21.

BOTDA [83].

**Temperature**

 **(°C)**

> Cheng Feng\*, Jaffar Emad Kadum and Thomas Schneider Institute for High Frequency Technology, Technical University of Braunschweig, Braunschweig, Germany

\*Address all correspondence to: cheng.feng@ihf.tu-bs.de

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
