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

Fringe projection techniques: Whither we are?

In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. Fibre Bragg grating (FBG) sensors have emerged as a reliable, in situ, non-destructive tool for monitoring, diagnostics and control in civil structures. The versatility of FBG sensors represents a key advantage over other technologies in the structural sensing field. In this article, the recent research and development activities in structural health monitoring using FBG sensors have been critically reviewed, highlighting the areas where further work is needed. A few packaging schemes for FBG strain sensors are also discussed. Finally a few limitations and market barriers associated with the use of these sensors have been addressed.

Fibre Bragg gratings in structural health monitoring—Present status and applications

We present a comprehensive overview of sensor technology exploiting optical whispering gallery mode (WGM) resonances. After a short introduction we begin by detailing the fundamental principles and theory of WGMs in optical microcavities and the transduction mechanisms frequently employed for sensing purposes. Key recent theoretical contributions to the modeling and analysis of WGM systems are highlighted. Subsequently we review the state of the art of WGM sensors by outlining efforts made to date to improve current detection limits. Proposals in this vein are numerous and range, for example, from plasmonic enhancements and active cavities to hybrid optomechanical sensors, which are already working in the shot noise limited regime. In parallel to furthering WGM sensitivity, efforts to improve the time resolution are beginning to emerge. We therefore summarize the techniques being pursued in this vein. Ultimately WGM sensors aim for real-world applications, such as measurements of force and temperature, or alternatively gas and biosensing. Each such application is thus reviewed in turn, and important achievements are discussed. Finally, we adopt a more forward-looking perspective and discuss the outlook of WGM sensors within both a physical and biological context and consider how they may yet push the detection envelope further.

/pdf/whispering-gallery-mode-sensors-3vzjirob2b.pdf

Whispering gallery mode sensors

Fiber optic sensors have become indispensable tools for biomedical study because of their unique features such as (1) high sensitivity, (2) small footprint and endoscopic compatibility, (3) multiple agent distributive sensing capability, and (4) immunity from electromagnetic interference. In this chapter, we will provide a brief overview on the basic principle of fiber optic sensors, types of fiber optic sensors, and their applications to biomedical sensing. As a result of the page limitation, important work in this area may not be included in this chapter. Readers may find those contents in the listed reference material.


Keywords:

fiber optic sensors;
light;
sensing mechanism;
biomedical sensing

Fiber Optic Sensors

Calibration-based phase-shifting projected fringe profilometry for accurate absolute 3D surface profile measurement

We report on a novel chromatic confocal microscope system using supercontinuum white light generated from a photonic crystal fiber. The chromatic aberration of a pair of singlet lenses is employed to focus the different spectral components of the supercontinuum at different depth levels. An effective depth scanning range of 7 μm is demonstrated. The corresponding depth resolution is measured to be less than 1 μm (FWHM).

Chromatic confocal microscopy using supercontinuum light

A simple and highly sensitive phase-demodulation technique is proposed, and its use for a fiber Bragg grating strain sensor is experimentally demonstrated. Sampling a phase-modulated Mach–Zehnder output with controlled time delay produced two quadrature data streams that have relative quadrature phase difference (90°). The Bragg wavelength-dependent phase information is extracted by application of digital arctangent function and phase unwrapping to the quadrature signals. By use of this technique with a reference grating, strain sensing at as much as a 30-kHz sampling rate was obtained with strain resolution of 3.5 microstrains and 6 nanostrains/ Hzin quasi-static and dynamic strain measurements, respectively.

Shizhuo Yin

Papers

Fiber Optic Sensors

Calibration-based phase-shifting projected fringe profilometry for accurate absolute 3D surface profile measurement

Chromatic confocal microscopy using supercontinuum light

Fiber Bragg grating strain sensor demodulation with quadrature sampling of a Mach–Zehnder interferometer

Nonzero-order joint transform correlator