Brillouin fiber sensing using stimulated Brillouin scattering in fibers to measure temperature and stress with the features of high-spatial resolution, long sensing range, small measurement error, etc. Therefore, Brillouin fiber sensing becomes the hotspot in recent two or three decades. Through research and analysis on the progress of long range distributed Brillouin sensing, main limitations and key techniques are generalized in this paper. Long range sensing schemes based on time division multiplexing, frequency division multiplexing, pulse coding, wide-bandwidth frequency modulation and image processing methods are emphatically introduced here. With long range Brillouin sensors applied in practice, increasing demand for fast measurement emerges, which we believe will be dominant in the research of long range Brillouin fiber sensing in the future.

In this mini-review, recent advances in the fiber optofluidic lasers and passive fiber optofluidic sensors are introduced. Fiber optofluidic laser can detect the biochemical changes using its laser output as a sensing signal. The cross-section of fiber can be used as a microcavity, providing optical feedback. The microcavity enhances the light-matter interaction, thus increasing the sensitivity. Furthermore, the geometry of optical fibers is uniform, easy to be mass produced with low cost, can be used to realize highly reproducible and disposable optofluidic laser. Passive fiber optofluidic sensors are also introduced based on the laser induced force and photo-thermal effects, which is flexible, easy to be integrated, multi-functional and reconfigurable.

With the development of fiber Bragg grating (FBG) and FBG based resonant cavity writing and signal demodulation technique, the measurement precision and frequency bandwidth of FBG sensor continue to be improved. It can highly promote its application in several fields of high precision detection requirements, such as geophysical exploration, seismic observation and marine observation. At present, the development of high-precision and wide bandwidth FBG sensors still face some challenges of key devices and techniques, including high-fineness FBG based resonant and low-noise narrow-linewidth tunable laser, high-precision broadband FBG wavelength demodulation technique, large-scale networking technique and high-sensitivity signal pickup probe design. Firstly, this paper introduces the development of high-precision FBG sensing technique. Secondly, it focuses on the cord devices and key techniques required for high-precision FBG sensing system and their applications in geophysical exploration, seismic observations and ocean observations. Finally, the high-precision FBG sensing technique and its application are prospected. In order to provide references for the development and application of high-precision fiber Bragg grating sensing technology, this paper aims to analyze and summarize some of the core techniques involved in high-precision FBG sensing technique and its application and the key issues that need to be solved.

The polarization crosstalk of a fiber optic polarization component and device refers to the optical power coupling that occurs at a disturbance point between the two orthogonal polarized modes propagating in it. The distributed polarization crosstalk along with the light propagation direction is directly responsible for the optical polarization properties, for example, the polarization, elliptical polarization, and depolarization properties. It also indirectly reflects the manufacturing technique and the state of the ambient environment, for example, the stress and strain at the joint and fixed position, as well as the temperature. Thus, it is the comprehensive embodiment of the intrinsic performance of the fiber optic polarization component and device and the influence of environment. It is expected to be a general characteristic parameter for online testing, diagnosis, and evaluation of the performance of the fiber optic polarization component and device. The best measurement method for distributed polarization crosstalk till now is the optical coherence domain polarimetry (OCDP). It is based on the white light interferometry and accurately measures the position and amplitude of the distributed polarization crosstalk using a scanning white light interferometer to realize interference between different polarized modes. It has the merits of ultrahigh sensitivity, ultra-wide dynamic range, and ultra-long measurable length. This review paper takes the polarization maintaining fiber coil and multifunctional integrated optical modulator as examples of distributed polarization crosstalk measurement and application. Firstly, the measurement principle of distributed polarization crosstalk based on the OCDP is introduced. Secondly, the measurement error sources and corresponding suppression methods are reviewed. Thirdly, the accurate measurement results of the fiber optic polarization component and device at different temperature are demonstrated. In the end, it outlooks the development of distributed polarization crosstalk measurement considering the complicated and changeable operation environment of the fiber optic polarization component and device.

As the core technology of distributed fiber-optic sensing, optical reflectometry may realize the non-destructive measurement at a remote position. It can be used to retrieve the distributed information such as reflectance, refractive index, polarization state along the optical fiber, and to diagnose the irregular “event” on fiber- optic links. For some high-end fields, such as the fault diagnosis on the fiber-to-the-home (FTTH) access network, the deformation monitoring on large generating units and large transformers, and the security monitoring on structures of airplane wings, the requirements on spatial resolution and measurement range of the sensing technologies are very high. In this paper, we summarized the research status on state-of-art optical reflectometry technologies, and reviewed the advances of key technologies on optical reflectometry with ultra-high spatial resolution and long measurement range. We proposed three different methods to improve the performance, and tried to promote their applications on distributed fiber-optic sensing systems.

Based on the fiber’s characteristics of both sensing and transmission for physical signal, distributed fiber sensing system can realize long-distance and continuous measurement of the strain, temperature and vibration along fiber, which has a great promise in applications of the perimeter security, electric wire and pipeline monitoring, structural health diagnosis for large infrastructure, and so on. The occurrence of events or failures usually causes the changes of multiple parameters such as vibration, strain and temperature, whose measurement contributes to fault diagnosis and intrusion recognition along sensing fiber. This paper overviews the recent progress in distributed fiber sensing systems, including wide-frequency vibration measurement based on Rayleigh scattering, dynamic measurement of strain based on Brillouin scattering and multi-parameter measurement based on multiple scattering mechanisms.

Optical fiber sensing system depends closely on the quality of the laser source, because laser parameters, such as the power stability, linewidth and phase noise, have a great impact on the performance of the fiber sensing system in such parameters as the maximum measuring distance, precision, sensitivity and noise characteristics. Therefore, the related high quality laser source has caused much attention these years. In this article, a brief review on the development of the laser source for fiber sensing is presented. Laser applications in optical fiber sensing are emphasized with the utilization of the narrow-linewidth laser, tunable laser and broadband light source. Finally, the main limiting factors and kernel technology of laser source for the optical fiber sensing are summarized. In order to achieve high performance of optical fiber sensing, the availability of the ideal ultra-narrow-linewidth and ultra-stable laser, which could be tuned at a desired wavelength span and tuning rate, will be definitely one of the main research directions of the future optical fiber sensing.

Optical fiber acoustic sensors are a kind of acoustic sensors that use optical fibers as light-propagating media or detection units. Compared to traditional electro-acoustic sensors, it features high sensitivity, broad-band frequency response, anti-electromagnetic interference etc, thus very promising for national security, industrial non-destructive testing, medical diagnostics, consumer electronics etc. Optical fiber acoustic sensors are classified, in terms of the coupling mode between acoustic field and light, as indirect and direct coupling types. The former presents some problems such as uneven frequency response, narrower bandwidth, and smaller dynamic range due to the frequency response features of the acoustic coupling materials, while the latter has overcome these shortcomings and thus possesses broad development potential.

In this paper, the unique properties of the hollow-core photonic bandgap fiber (HC-PBF) are reviewed, and a variety of sensing and device applications of this type of fiber in recent years are introduced. Low-loss light transmission in air core is an important characteristic of the HC-PBF, which provides light-matter interaction channel with high energy density and long interaction distance. In addition, the air-propagation of the light in fiber also reduces the impacts of fiber material properties (such as infrared absorption, thermos-optical effect) on propagating light, hence offers an efficient platform for the sensing applications such as trace gas / liquid detection, optical fiber gyro sensing. The fine micro-structure in HC-PBF exhibits novel mechanical and thermal properties, which would be beneficial to the sensing applications such as sound wave and vibration detection. The HC-PBF’s porous structure can also be locally modified by using various post-processing techniques, such as local heat treatment, micromachining and selective filling, which would enable further function extension or performance enhancement. The flexibility of the fiber has been used to develop new optical fiber devices, such as grating, polarizer and polarization interferometer. At present, the development of HC-PBF sensing technology has greatly expanded the sensing ability and application range of optical fiber. It is an important direction for the development of all-optical devices and optical integration technology.

The paper reviews the major techniques of specialty fiber fabrication. It primarily reports the progress of panda-type polarization maintaining fiber, spun fiber, specialty fibers for harsh environment and those for novel distributed sensing applications. Compared with the sensing systems utilizing conventional communication fiber, the fiber optic sensors based on specialty fibers show evident advances in performance. Additionally, the development of specialty fibers facilitates the advent of novel sensing mechanisms.

In this paper, two fiber reinforced polymer/plastic (FRP) encapsulated fiber Bragg grating (FBG) sensors were installed on the two sides of the angle steel beam, which was used to measure the displacement and direction of the diagonal steel beam, so as to realize the health inspection of the angle steel structure. The sensors were respectively installed on the different positions of angle steel beam, and the relationship between displacement and strain transmission of angle steel beam was simulated by the finite element analysis. The optimum design of sensors installation were discussed and the experimental verification was carried out. The simulation and experimental rex sults show that the sensor has the capacity to discriminate the direction and measure the size of one side of the angle steel beam displacement when installed in a reasonable position. To realize the health monitoring by using optical fiber sensors on the structures composed by angle steel, such as bridges, electric towers and cranes, and so on, a basic research was provided.

This paper propose a route to decorated end facet of single mode optical fibers with colloidal photonic crystals and present the principle for this structure to be used as relative humidity sensing. The approaches of preparing PS colloidal crystals, composite colloidal crystals, and SiO2 inverse opals on the end faces of optical fibers by vertical deposition was studied. The prepared colloidal crystals and inverse opal were structurally characterized, and the reflection spectra of the photonic crystals-modified microstructure optical fibers was measured. The relative humidity sensing characteristics of composite photonic crystals decorated microstructure optical fibers were tested. Finally, a capillary-fiber structure was proposed to improve the quality and mechanical stability of the colloidal crystals fabricated on the fiber endfaces.