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

Electron‐spin‐resonance and density gradient column techniques have been used to measure and characterize the effect of radiation on the electronic and mechanical properties of a low‐thermal‐expansion glass ceramic. Defect centers attributed to Zn+, oxygen hole centers (OHCs), Fe3+, Ti3+, and/or Zr3+, and two types of centers associated with arsenic have been observed; the radiation‐induced compaction has been tentatively correlated with the OHC concentration.

Radiation effects on a low‐thermal‐expansion glass ceramic

Magnetization studies of amorphous antiferromagnetism in manganese phosphate glass

Loading experiments have been carried out on a flat panel and C-channels fabricated by the Continuous Resin Transfer Molding (CRTMTM) process. Arrays of fiber Bragg grating (FBG) strain sensors written during fiber draw were embedded in the structures, and the strains measured by these distributed sensors are compared with the results of surface-mounted resistance strain gages (RSG's) and FBG arrays. Reproducibility of the strains measured by an embedded FBG array was demonstrated during cyclical loading of a C-channel, and survivability and reliability of the array was established when the structure was loaded to failure. Discrepancies between the results reported by the embedded FBG's and surface- mounted RSG's and FBG's are attributed to deflections and/or distortions of the embedded FBG by the structural fibers during CRTMTM processing.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Demonstration of distributed strain sensing in production scale instrumented structures

A phase-conjugate mirror was used in the amplifier section of a KrF excimer laser to fabricate fibre Bragg gratings in singlemode Ge-doped silica core fibres with an uncompensated interferometer. Reflectivities as high as 26% and FWHM linewidths of 5.5 GHz at 0.817 µm were obtained in as-drawn fibre with a single pulse exposure.

Single pulse fabrication of fibre Bragg gratings using a phase-conjugated KrF excimer laser

We present a method for sensing both bending and twisting in an optical fiber which is compatible with extensive multiplexing. The technique employs a multi-core fiber design, high-performance static strain sensing, and robust reconstruction algorithms.

E. J. Friebele

Papers

Radiation effects on a low‐thermal‐expansion glass ceramic

Magnetization studies of amorphous antiferromagnetism in manganese phosphate glass

Demonstration of distributed strain sensing in production scale instrumented structures

Single pulse fabrication of fibre Bragg gratings using a phase-conjugated KrF excimer laser

Bend and twist sensing in a multi-core optical fiber