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 work presents an overview of progress and developments in the field of fiber optic sensor technology, highlighting the major issues underpinning recent research and illustrating a number of important applications and key areas of effective fiber optic sensor development.

http://snake.persiangig.com/document/sensor1.pdf

Fiber optic sensor technology: an overview

Robotic medical instrument systems and associated methods utilizing an optical fiber sensors such as Bragg sensor optical fibers. In one configuration, an optical fiber is coupled to an elongate instrument body and includes a fiber core having one or more Bragg gratings. A controller is configured to initiate various actions in response thereto. For example, a controller may generate and display a graphical representation of the instrument body and depict one or more position and/or orientation variables thereof, or adjust motors of an instrument driver to reposition the catheter or another instrument. Optical fibers having Bragg gratings may also be utilized with other system components including a plurality of working instruments that are positioned within a sheath lumen, an instrument driver, localization sensors, and/or an image capture device, and may also be coupled to a patient's body or associated structure that stabilizes the body.

Robotic instrument systems and methods utilizing optical fiber sensors

The spectral behaviour of two superimposed fibre gratings having different Bragg wavelengths (850 and 1300 nm) with respect to strain and temperature has been studied. The results show that the ratio of sensitivity at two Bragg wavelengths is dependent on strain and temperature, which can be used for simultaneous measurement of these parameters using a single sensing element.

/pdf/discrimination-between-strain-and-temperature-effects-using-1xlw6ng6ys.pdf

Discrimination between strain and temperature effects using dual-wavelength fibre grating sensors

http://www.qpsmonitoring.com/applicationreview.pdf

Recent progress in applications of in-fibre Bragg grating sensors

This paper describes a new method that we have developed to generate Bragg grating filters in germania-doped communication fibers and discusses their applications as sensors. The gratings are formed by exposing a short section of the core, through the side of the fiber, to an interference pattern of intersecting coherent beams of UV light. A permanent periodic index modulation is produced by the interference fringes. It forms a phase grating which acts as a band rejection filter, passing wavelengths that are not in resonance with the grating and strongly reflecting wavelengths which satisfy the Bragg condition. The grating wavelength is sensitive to changes temperature and strain. Measurements of the shift in Bragg wavelength with these quantities are reported and compared with computed estimates of the sensitivity. A large number of independent gratings can be easily written along a length of fiber to make a distributed sensor system. We have also demonstrated that Bragg gratings can wavelength tune laser diodes, which could be used for detecting the wavelength shift of the Bragg sensors.

Fiber Optic Bragg Grating Sensors

A variable light filtering arrangement (10) includes at least one optical fiber section (11) including a waveguiding core (13), and at least one permanent Bragg grating region (12) in the optical fiber section. The grating region includes a plurality of grating elements constituted by periodic refractive index variations of a predetermined initial periodicity and cumulatively redirecting, of the light launched into the core for guided propagation therein, that having an axial wavelength within a narrow band around a central wavelength that is determined by the periodicity and refractive index variations of the grating elements. At least one of the periodicity and refractive index variations of the grating region is controlledly modified in such a manner as to temporarily change the central wavelength within a predetermined wavelength range.

Variable optical fiber bragg filter arrangement

A distributed, spatially resolving optical fiber strain gauge in which the core of the optical fiber is written with periodic grating patterns effective for transmitting and reflecting light injected into the core. Spectral shifts in the transmitted and reflected light indicate the intensity of strain or temperature variations at positions of the grating corresponding to the associated wavelengths of injected light.

Distributed, spatially resolving optical fiber strain gauge.

A tunable optical waveguide laser arrangement includes a solid optical waveguide capable of guiding light along an axis between axially spaced ends thereof and being at least in part of an excitable material that emits light in response to stimulation by light. Stimulating light is launched into the waveguide for axial propagation therein and attendant emission of light by the excitable material. Two end reflectors are situated in the waveguide, each at one of the axially spaced ends thereof and extending normal to the axis to delimit a laser cavity. Each of the reflectors is constituted by a Bragg grating consisting of a multitude of axially consecutive grating elements constituted by periodic refractive index perturbations with a given periodicity. The length of the cavity, the peak reflectivity of the Bragg gratings and the gain of the excitable material are so coordinated with one another as to enable lasing in only a single longitudinal mode. The length of that portion of the optical waveguide that incorporates the two Bragg gratings and an intervening region of the optical waveguide is uniformly controlledly varied with attendant continuous tuning of the laser output wavelength without longitudinal mode hopping.

Continously tunable single-mode rare-earth doped pumped laser arrangement

An optical waveguide light tapping arrangement includes an optical waveguide having solid portions that guide light in a first path along a longitudinal axis, with at least one grating region being embedded in the solid portion at a location remote from its end portions. The grating region includes a multitude of grating elements extending with a substantially equal longitudinal spacing at an oblique angle relative to the longitudinal axis to redirect light reaching the grating elements between the first path and at least one second path extending externally of the waveguide at an angle relative to the longitudinal axis that depends on the oblique angle. When light is directed in one of the first and second paths toward the grating region, it is redirected by the grating elements into the respectively other of the second and first paths with attendant in-phase combination in the other path of light having a wavelength within a narrow range around a central wavelength that is in a predetermined relationship to the spacing of the grating elements. The light propagating in the other path can then be captured. The grating elements are formed in the core by exposing the core to an interference pattern of two ultraviolet radiation beams that are symmetrical with respect to a plane extending at the oblique angle relative to the core axis.

William H. Glenn

Papers

Fiber Optic Bragg Grating Sensors

Variable optical fiber bragg filter arrangement

Distributed, spatially resolving optical fiber strain gauge.

Continously tunable single-mode rare-earth doped pumped laser arrangement

Optical waveguide embedded light redirecting Bragg grating arrangement