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

The effect of (gamma) and proton radiation on the optical attenuations at 980, 1300, and 1550 nm has been measured in two Lucent Technologies erbium-doped fibers (EDFs) designed for use in amplifiers pumped at 980 nm. Growth of the induced loss at the 3 wavelengths followed a power law of dose with an exponent of approximately 0.8 independent of fiber, radiation type or dose rate. The incremental attenuation was found to have only a weak dependence on dose rate. The recovery could be described by the sum of 3 exponential decay terms, but simple color center models overestimated the effect of dose rate.

Space radiation effects on erbium-doped fibers

The radiation‐induced optical attenuation has been measured over a wide range of dose and time in state‐of‐the‐art step‐ and graded‐state 60Co and pulsed electron irradiation. Results are reported for previously uncharacterized silica fibers containing dopants such as Ge,P,B,F,Tl, and Cs. At short times following the irradiation, fibers which contain Ge exhibit an extremely high attenuation that is not observed when these fibers contain P. Recovery is typically more complete in the silica core fibers than in the doped silica core fibers, which can have losses 25–1000 times the intrinsic loss 3 months after an irradiation of 105–106 rad.

Effect of ionizing radiation on the optical attenuation in doped silica and plastic fiber‐optic waveguides

Thallium in $a$-${\mathrm{As}}_{2}$${\mathrm{Se}}_{3}$ reduces transient hole transport but has no effect upon the photoluminescence and photoinduced ESR. The results are discussed in terms of the recent models of charged defects in chalcogenides.

Hole Transport, Photoluminescence, and Photoinduced Spin Resonance in Thallium-Doped Amorphous As 2 Se 3

Ferromagnetic resonance (FMR) spectra were obtained at 9 and 35 GHz for particles of metallic iron precipitated in fused silica containing 1–120 ppm Fe. Accurate g values and anisotropy constants K1, K2 and K3 were extracted by computer simulation of the powder pattern line shapes, assuming negligible shape anisotropy. One sample, melted under a He‐H2O atmosphere, exhibited anisotropy constants identical with published values for pure α–iron and a g value of 2.081±0.002. Samples strongly reduced in H2 displayed smaller values of K1, consistent with expectation for alloying of the Fe with up to 20% Si. These K1 values were shown to be statistically distributed and linearly correlated with the g values in the range 5?at.%Si?20. All samples displayed increases ∼ 5–10% in apparent K1 value with increasing frequency, either as‐delivered or after aging. It is hypothesized that the latter effects are due to the formation of a magnetic iron oxide layer at the metal‐glass interface.

Ferromagnetic resonance of spherical particles of α‐iron precipitated in fused silica

The optical attenuation induced in two erbium-doped fibers by 60Co (gamma) -ray exposures to 200 krad has been measured at 3 different dose rates, approximately, 35, 1000, and 20,500 rad/min. The growth of the induced loss was measured at 980, 1300, and 1500 nm. In some instances recovery of the loss after exposure was also measured. The effect of temperature on radiation-induced loss was examined by irradiating one of the erbium-doped fibers at three different temperatures, -54, 30, and 80 C. A simple physical model describing the thermal annealing process of the induced loss in the fibers is presented. The model yields expressions, with only two adjustable parameters, which describe the dose rate and temperature dependence of both the radiation-induced loss growth and recovery kinetics. The simple model accurately describes the form of the growth and recovery kinetics but overestimates the dependence of induced loss on dose rate and temperature.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

E. J. Friebele

Papers

Space radiation effects on erbium-doped fibers

Effect of ionizing radiation on the optical attenuation in doped silica and plastic fiber‐optic waveguides

Hole Transport, Photoluminescence, and Photoinduced Spin Resonance in Thallium-Doped Amorphous As 2 Se 3

Ferromagnetic resonance of spherical particles of α‐iron precipitated in fused silica

Projecting the performance of erbium-doped fiber devices in a space radiation environment