Information technology is the cornerstone that supports the development and social life of today's world, with its important component of sensing technology. Fiber optic sensing technology utilizes light waves as information carriers and transmission media to achieve the collection and measurement of signals in the environment. As an important branch of fiber optic sensing technology, distributed fiber optic sensing can achieve long-distance, high-resolution, and highly sensitive continuous distributed detection, obtaining two-dimensional spatio-temporal distribution information. Compared to the other two types of scattering distributed sensing, the system based on Rayleigh scattering features higher backscattering power and faster response and is more suitable for detecting dynamic and static signals such as sound waves and strain. With the increasing demands for engineering applications such as resource exploration, structural health monitoring, and underwater exploration, distributed fiber optic sensing has developed rapidly in recent years.

At present, most distributed sensing systems usually employ single-mode fiber (SMF) as the sensing medium. However, its Rayleigh backscattering signals are extremely weak, resulting in poor signal-to-noise ratio (SNR) of sensing light, which in turn causes poor SNR of demodulation signals in distributed sensing systems. Additionally, the intensity fading effect induced by high laser coherence can cause sensing blind spots, and the light intensity fading can also result in poor sensing consistency among multi-channels. Meanwhile, due to the influence of optical transmission loss, the sensing SNR of ordinary non-amplification SMF optic systems is limited at long distances. The fully continuous characteristics of backscattering signals in optical SMFs can also result in mutual limitations between the system response bandwidth and sensing distance. Therefore, scattering enhanced special optical fibers are introduced into distributed sensing systems based on Rayleigh scattering. By continuously changing the fiber material and structure, or introducing discrete scattering enhancement mechanisms, the distributed sensing limitations of ordinary optical SMFs are overcome in specific sensing parameters, sensing performance, and other aspects.

Thus, in some specific application scenarios that require high-precision detection, scattering enhanced optical fiber has irreplaceable advantages. In recent years, numerous research institutions and researchers have conducted research on scattering enhanced fiber optical distributed sensing systems and obtain significant results.

We focus on analyzing the scattering characteristics and noise suppression mechanisms of scattering enhanced microstructured sensing fibers, and elaborate on the types and precision preparation techniques of scattering enhanced fibers. Meanwhile, the performance improvement techniques of DAS and OFDR systems based on scattering enhanced microstructured fiber are summarized (Fig. 5 and Table 1), and the mechanism and typical applications of DAS SNR and sensitivity enhancement are discussed. The research progress of scattering enhanced hydrophone composite cables is elaborated (Table 2), and the construction of highly sensitive distributed hydrophone systems and their hydrophone applications are introduced (Table 3). Additionally, we summarize the high-density grating scattering enhanced microstructured fiber to achieve high-resolution, highly sensitive, and highly reliable fully distributed strain sensing based on optical frequency domain reflectometry (Figs. 10 and 11). Combined with highly reliable reconstruction algorithms, scattering enhanced microstructured spiral multi-core optical fibers are designed to achieve high-precision three-dimensional shape sensing and practical applications (Table 4).

In summary, we study the mechanism of distributed sensing efficiency enhancement from the perspective of scattering enhanced special optical fibers, introduce the automatic precision fully continuous writing technology, and focus on the principles of its optical time domain and optical frequency domain distributed sensing systems. Meanwhile, the research progress of distributed acoustic sensing and optical frequency domain reflection technology based on scattering enhanced microstructured fiber is summarized, and typical engineering applications based on the above two systems are summarized.

In the future, distributed sensing technology based on scattering enhanced optical fibers can still be improved and expanded in various aspects. For example, the material and structural parameters of scattering enhanced microstructured fiber can be optimized, and the high-efficiency and stable writing preparation process can be improved. Additionally, the scattering enhancement characteristics of optical fibers can be combined with intelligent AI algorithms to optimize sensing demodulation accuracy. Meanwhile, the high precision 3D shape sensing and scattering enhanced fiber distributed hydrophone can be further extended to various cross applications. As the scattering enhanced special sensing fibers further develop in the future, distributed sensing systems based on scattering enhanced fibers will play an irreplaceable role in most fields.