## 7 Conclusions
On the contrary, Brillouin optical correlation-domain technologies have advantages for applications that require a moderate measurement range, such as for example a 100-m order or km order, and a high spatial resolution, such as for example in the order of centimeters. The most important feature of the BOCDA and the BOCDR is their random accessibility. At multiple points selected arbitrarily along the fiber, time-resolved strain measurements can be done simultaneously. Considering this features positively, SHM schemes using BOCDA technologies for aircraft wings and bodies have been under development. The dynamic strain measurement capability of the correlation domain-distributed sensing technologies also shows the possibility of providing the SHM functions for the social infrastructures, such as buildings, bridges, and highways, especially under earthquake vibration conditions. Utilizing a mm-order spatial resolution, the diagnosis of optical integrated circuits, such as planar lightwave circuits (PLC), is another possible application of the BOCDA systems. Prototype models of BOCDA and BOCDR systems have already been fabricated or have been under fabrication, under the support of national funding agencies in Japan. For example, a BOCDA prototype model has already provided us with the total performances of a three-cm spatial resolution, 500-m measurement range, 60-\(\upmu\epsilon\) strain accuracy, and 160-times/s random access measurement speed. In this model, the function of the discriminative and distributed measurement of both strain and temperature has also been included. The author would like to expect commercially available equipment for BOCDA and BOCDR systems in the near future. As another concept of distributed fiber-sensing technology, a Rayleigh scattering-based one has been developed that can be available on a commercial base, which uses a distribution measurement principle such as the frequency modulated continuous wave technique [114]. This technology realizes spatial resolution in the order of sub-mm to mm, a 10-50 m measurement range, and a strain accuracy of around 30 \(\upmu\epsilon\)[115]. These fiber optic nerve systems described above have different distributed measurement principles, and thus show different distributed measurement performances. Therefore, these all have the possibility of being applied to varieties of applications that require different specifications. The author would like to expect that the safety and security of society would be enhanced by introducing the SHM schemes that use these technologies. This review paper was totally written by the author. This paper was written as a review paper. The author received no external funding for the preparation of this paper. The technologies described in this paper have mainly been studied in the University of Tokyo, Tokyo, Japan, from 1990 to 2017. Since April, 2017, the author has been working in Toyota Technological Institute, Nagoya, Japan. The researches in TTI is also included partly in this paper. The author would like to express sincere thanks to all the laboratory members for their contributions to the researches and developments of the technologies described in this paper. The author would like to acknowledge also to the researchers in companies and institutions, with whom we have had fruitful collaborations related to the technologies. The The author declares no conflict of interest.