This work presents a detailed review of the development of distributed acoustic sensors (DAS) and their newest scientific applications. It covers most areas of human activities, such as the engineering, material, and humanitarian sciences, geophysics, culture, biology, and applied mechanics. It also provides the theoretical basis for most well-known DAS techniques and unveils the features that characterize each particular group of applications. After providing a summary of research achievements, the paper develops an initial perspective of the future work and determines the most promising DAS technologies that should be improved.

A new method for monitoring the nonlinearities perturbing the optical frequency sweep in high speed tunable laser sources is presented. The swept-frequency monitoring system comprises a Mach-Zehnder interferometer and simple signal processing steps. It has been implemented in a coherent optical frequency domain reflectometer which allowed to drastically reduce the effects of nonlinear sweep, resulting to a spatial resolution enhancement of 30 times.

In this paper, we discuss the operation principles, challenges and application areas of optical frequency domain reflectometry technique. A review of OFDR systems is given considering both Incoherent-OFDR and Coherent-OFDR groups. Results obtained by different research groups are compared in terms of performance characteristics, and future perspectives. Recent progresses obtained within our laboratory are also presented.

Optimal operation, reduced energy consumption, longer service availability, and high safety level are the major concerns in today’s railway transport systems. Smart monitoring systems should address these issues without interrupting railway operability. Many successful works have been carried out to provide railway monitoring functions using fiber Bragg grating (FBG) sensors on rail. Most of them are based on strain measurement due to the train passage. This paper presents a highly sensitive means for railway monitoring based on vibration measurement. FBG accelerometers placed on sleeper have been employed as sensor heads, which significantly facilitated the field sensor installation work compared to the positioning on the foot of the rail. An optimized signal demodulation algorithm has been effectively used to extract from the accelerometer traces both the axle number and the average speed information. Excellent capability of the developed system to obtain both parameters has been demonstrated by the way of field trials carried out on a Belgian railway line, during its normal operation. Easy installation, multi-function diagnosis, good data integrity, and compatibility with fiber optic sensors make the proposed sensor a good candidate for railway monitoring applications.

Motivations, challenges and requirements of optical layer monitoring in PONs are discussed. An exhaustive review of monitoring systems is given considering both time-division multiplexed PON (TDM-PON) and wavelength-division multiplexed PON (WDM-PON) cases.

We present the analysis of a quasi-distributed fiber sensor based on the concatenation of identical low-reflective fiber Bragg gratings (FBGs) taking into account both multireflection and spectral-shadowing crosstalks. This allows obtaining more realistic values of the design parameters such as the maximum number of sensing points, the reflectivity of the gratings, and the distance between the sensing points.