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

The historical beginnings of photosensitivity and fiber Bragg grating (FBG) technology are recounted. The basic techniques for fiber grating fabrication, their characteristics, and the fundamental properties of fiber gratings are described. The many applications of fiber grating technology are tabulated, and some selected applications are briefly described.

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Fiber Bragg grating technology fundamentals and overview

This tutorial/survey paper: (1) provides a concise point of departure for researchers and practitioners alike wishing to assess the current state of the art in the control and monitoring of civil engineering structures; and (2) provides a link between structural control and other fields of control theory, pointing out both differences and similarities, and points out where future research and application efforts are likely to prove fruitful. The paper consists of the following sections: section 1 is an introduction; section 2 deals with passive energy dissipation; section 3 deals with active control; section 4 deals with hybrid and semiactive control systems; section 5 discusses sensors for structural control; section 6 deals with smart material systems; section 7 deals with health monitoring and damage detection; and section 8 deals with research needs. An extensive list of references is provided in the references section.

Structural control: past, present, and future

Review of the present status of optical fiber sensors

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

This paper reports on the application of a calibrated, narrow-linewidth, single-frequency, continuously wavelength-tunable erbium fiber laser to the interrogation of a multipoint Bragg grating temperature sensor. The fiber laser was wavelength-tuned, through an array of three fiber Bragg grating sensors, to determine the temperature of each individual grating. The temperatures of the three gratings were measured as a function of grating Bragg wavelength. The minimum wavelength resolution, due to electro-mechanical repeatability, of the fiber laser source/analyzer was determined to be approximately 2.3 picometers. This corresponds to a frequency resolution of approximately 300 MHz. >

Fiber laser source/analyzer for Bragg grating sensor array interrogation

The operation of single- and multipoint active fiber sensors for both strain and temperature measurements is reported. An active fiber source consists of a pair of wavelength-matched Bragg gratings formed in a rare earth doped fibre, and when, optically pumped, lase in a narrow bandwidth around the Bragg wavelength. The primary advantage of an active sensor over a passive sensor is a significant increase in signal-to-noise ratio. >

Single- and multipoint fiber-laser sensors

The effective pump rate for Er-doped fibers by using Yb codoping is analyzed. We show that the level of the pump power required to suppress the ion-pair induced self-pulsing in Er-doped fiber lasers can be significantly decreased by using Yb:Er-codoped fibers due to the increased effective pump rate. Our results show the potentiality of developing stable single-frequency or high-repetition-rate mode-locked fiber lasers by using high-gain Yb:Er-codoped fibers with laser diodes as pump sources.

Effects of Yb:Er-codoping on suppressing self-pulsing in Er-doped fiber lasers

For Er-doped fiber lasers, we show that the fluctuation of lasing power caused by resonant pump-power perturbations is inversely proportional to the lifetime of photon in the laser cavity. Analysis shows that Er-doped fibers with high-gain coefficient are favorable for fiber lasers in the view of point of suppressing the lasing-power instability caused by the resonant pump perturbation. The results obtained are especially useful for single-frequency Er-doped fiber lasers which have a very short cavity length, i.e., a short lifetime of photon in the cavity.

Analysis of Er-doped fiber laser stability by suppressing relaxation oscillation

Grating gain must be accounted for when designing single-frequency fiber lasers which utilize intracore, erbium-doped, Bragg reflectors for cavity feedback, and mode selectivity. A closed-form solution, derived through coupled mode theory for the spectral reflectivity of an intracore Bragg phase grating in an amplifying fiber is derived and applied to the design of single-mode fiber lasers. Both analytical and experimental results are presented. >

P.K. Cheo

Papers

Fiber laser source/analyzer for Bragg grating sensor array interrogation

Single- and multipoint fiber-laser sensors

Effects of Yb:Er-codoping on suppressing self-pulsing in Er-doped fiber lasers

Analysis of Er-doped fiber laser stability by suppressing relaxation oscillation

Modeling of short, single-frequency, fiber lasers in high-gain fiber