A random fiber laser does not need a traditional resonant cavity and only uses the multiple scattering of disordered media to provide feedback to achieve laser output. Therefore, it has the advantages of a simple structure, narrow linewidth, and low noise and is particularly suitable for fiber optic sensors. This paper provides an introduction to the categories and corresponding principles of random fiber lasers. The research progress of random fiber lasers in the sensing field in recent years, including various aspects of random fiber lasers as low-noise light sources or sensitive elements for fiber sensing systems, is the main focus. Finally, the future development trend of random fiber lasers for optical fiber sensors is explored.

The temperature and strain fields monitoring during the preparation process of buoyancy materials, as well as the health status after molding, are important for mastering the mechanical properties of buoyancy materials and ensuring the safety of operators and equipment. This paper proposes a short and high-density femtosecond fiber Bragg grating (fs-FBG) array based on different temperature coefficients fibers. By optimizing the parameters of femtosecond laser point-by-point writing technology, high-performance fs-FBG arrays with millimeter level gating length and millimeter level spatial resolution were prepared on two types of fibers. These were successfully embedded in buoyancy materials to achieve in-situ online monitoring of the curing process and after molding. The experimental results show that the fs-FBG array sensor has good anti-chirp performance and achieves online monitoring of millimeter-level spatial resolution. Intelligent buoyancy materials can provide real-time feedback on the health status of equipment in harsh underwater environments. The system can achieve temperature monitoring with an accuracy of 0.56 °C and deformation monitoring with sub-millimeter accuracy; the error is in the order of micrometers, which is of great significance in the field of deep-sea exploration.

The embedded high-resolution random fiber laser acoustic emission (RFL-AE) sensor for in-situ monitoring of buoyancy material is demonstrated. Our proposed embedded RFL-AE sensor can directly couple inside the solid buoyant materials (sBm) and be expected to detect different AE signals mechanism of SBM without any medium. The randomly chirped grating array (RCGA) provides effective random distributed feedback and is embedded inside the SBM to act as an AE sensing element. Many steep peaks can be provided by the multiple-interfering refection spectrum of RCGA over a broad spectral range, which significantly suppresses chirping phenomenon caused by the thermal stress of SBM and realizes in-situ performance monitoring of buoyant materials under high pressure. The test results show that our proposed RFL-AE sensor is highly responsive to continuous and burst AE signals of SBM. The measured resolution of AE signal is 215 fε/√Hz, which provides a potential embedded laser AE monitoring scheme for damage detection of SBM-associated composite material.