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

In this paper, we describe the spectral characteristics that can be achieved in fiber reflection (Bragg) and transmission gratings. Both principles for understanding and tools for designing fiber gratings are emphasized. Examples are given to illustrate the wide variety of optical properties that are possible in fiber gratings. The types of gratings considered include uniform, apodized, chirped, discrete phase-shifted, and superstructure gratings; short-period and long-period gratings; symmetric and tilted gratings; and cladding-mode and radiation-mode coupling gratings.

Fiber grating spectra

We present a novel class of highly sensitive sensors based on long-period fiber gratings that can be implemented with simple and inexpensive demodulation schemes. Temperature, strain, and refractive-index resolutions of 0.65 °C, 65.75 μ∈, and 7.69 × 10−5, respectively, are demonstrated for gratings fabricated in standard telecommunication fibers.

Optical fiber long-period grating 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

The transmission of a mode guided by the core of an optical fiber through an ultraviolet-induced fiber grating when substantial coupling to cladding modes occurs is analyzed both experimentally and theoretically. A straightforward theory is presented that is based on the calculation of the modes of a three-layer step-index fiber geometry and on multimode coupled-mode theory that accurately models the measured transmission in gratings that support both counterpropagating (short-period) and co-propagating (long-period) interactions. These cladding-mode resonance filters promise unique applications for spectral filtering and sensing.

Cladding-mode resonances in short- and long-period fiber grating filters

We present a new class of long-period fiber gratings that can be used as in-fiber, low-loss, band-rejection filters. Photoinduced periodic structures written in the core of standard communication-grade fibers couple light from the fundamental guided mode to forward propagating cladding modes and act as spectrally selective loss elements with insertion losses act as backreflections <-80 dB, polarization-mode-dispersions <0.01 ps and polarization-dependent-losses <0.02 dB.

A. M. Vengsarkar

Papers

Long-period fiber grating as band-rejection filters