We review the recent developments in the area of optical fiber grating sensors, including quasi-distributed strain sensing using Bragg gratings, systems based on chirped gratings, intragrating sensing concepts, long period-based grating sensors, fiber grating laser-based systems, and interferometric sensor systems based on grating reflectors.

Fiber grating sensors

Review of the present status of optical fiber sensors

Recent research on fibre optic long-period gratings (LPGs) is reviewed with emphasis placed upon the characteristics of LPGs that make them attractive for applications in sensing strain, temperature, bend radius and external index of refraction. The prospect of the development of multi-parameter sensors, capable of simultaneously monitoring a number of these measurands will be discussed.

https://iopscience.iop.org/article/10.1088/0957-0233/14/5/201/pdf

Optical fibre long-period grating sensors: characteristics and application

In-fibre Bragg grating (FBG) sensors are one of the most exciting developments in the field of optical fibre sensors in recent years. Compared with conventional fibre-optic sensors, FBG sensors have a number of distinguishing advantages. Significant progress has been made in applications to strain and temperature measurements. FBG sensors prove to be one of the most promising candidates for fibre-optic smart structures. This article presents a comprehensive and systematic overview of FBG sensor technology regarding many aspects including sensing principles, properties, fabrication, interrogation and multiplexing of FBG sensors. It is anticipated that FBG sensor systems will be commercialized and widely applied in practice in the near future due to the maturity of economical production of FBGs and the availability of cost effective interrogation and multiplexing techniques.

https://iopscience.iop.org/article/10.1088/0957-0233/8/4/002/pdf

In-fibre Bragg grating sensors

The spectroscopic properties, structure and interconversions of optically active oxygen-deficiency-related point defects in vitreous silica are reviewed. These defects, the E′-centers (oxygen vacancies with a trapped hole or 3-fold-coordinated silicons), different variants of diamagnetic `ODCs' (oxygen-deficiency centers), and their Ge-related analogs play a key role in the fiber-optic Bragg grating writing processes. The controversy surrounding the structural models for the Si- and Ge-related ODCs is discussed and the similarity between the bulk and surface point defects in silica is emphasized. The possible interconversion mechanisms between 2-fold-coordinated Si, neutral oxygen vacancies and E′-centers are discussed. The effects of glassy disorder have a profound effect on defect properties and interconversion processes in silica.

Optically active oxygen-deficiency-related centers in amorphous silicon dioxide

Thermally generated paramagnetism in amorphous arsenic

The loss induced in polarization-maintaining (PM) fibers by low dose rate [<0.01 Gy/h, where 1 Gy = 100 rads(Si)] radiation exposure has been found to vary from <0.4 to ≈ 6 dB/km-10 Gy, depending on the wavelength of measurement and the fiber. Correlations have been established between low dose rate response and the “permanent” induced loss determined by fitting the recovery of the induced loss following high dose rate exposure to nth-order kinetics. Using this technique, both 0.85- and 1.3-μm PM fibers have been found which show virtually no permanent incremental loss and would therefore appear to be resistant to low dose rate radiation environments. The asymmetric stress inherent in PM fibers has been shown to reduce the permanent induced loss, while the recovery of the radiation-induced attenuation was found to be enhanced in fibers with Ge-F-doped silica clads.

Radiation-induced attenuation in polarization maintaining fibers: low dose rate response, stress, and materials effects.

Fiber Bragg gratings are of particular interest for distributed sensor applications such as embedded sensors for structural strain monitoring. This paper discusses the use of a wavelength division multiplexed fiber Bragg grating array for structural shape sensing and vibrational mode analysis. The gratings are surface attached to a cantilever beam and demodulated by a scanning fiber Fabry Perot filter to obtain strain information at different locations along the structure. A PC is used to read the strain information and perform static shape modeling of the beam.

Fiber optic Bragg grating array for shape and vibration mode sensing

The optical attenuation induced in polymer‐clad silica fiber‐optic waveguides by low‐dose ionizing radiation (0.5–14 MeV) has been found to be much greater than expected on the basis of previous high‐dose measurements. The radiation sensitivity is dependent upon the purity and OH content of the silica and upon the radiation history of the fibers, but it does not appear to depend upon the drawing conditions nor on the limited radiation‐induced loss in the polymer cladding. The damage is greater at short times following the irradiation, and the decay kinetics of different synthetic silica fibers are qualitatively the same.

Effect of ionizing radiation on the optical attenuation in polymer‐clad silica fiber‐optic waveguides

Photoluminescence (PL) and optically induced electron spin resonance (ESR) have been studied in As2Se3 glasses doped with Cu, Tl, I, Ag, In, and K and in B-doped As2S3 glass. In all cases there is no significant change in PL efficiency or intensity of induced ESR until dopant concentrations exceed ∼1 at.%. These results are in marked contrast the strong dependence of transient hole transport upon dopant concentration in the same glasses. These parallel but contrasting observations are discussed in terms of the predicted effects of dopants on defects in chalcogenide glasses postulated by Mott on the basis of the charged defect model of Mott, Davis and Street (MDS). PL and ESR studies of the AsSe glass system have revealed that oxygen contamination can severely quench PL efficiency and ESR intensity for As concentrations

E. J. Friebele

Papers

Thermally generated paramagnetism in amorphous arsenic

Radiation-induced attenuation in polarization maintaining fibers: low dose rate response, stress, and materials effects.

Fiber optic Bragg grating array for shape and vibration mode sensing

Effect of ionizing radiation on the optical attenuation in polymer‐clad silica fiber‐optic waveguides

The effects of impurities upon photoluminescence and optically induced paramagnetic states in chalcogenide glasses