Optical fibre grating

Fig. 8.10. Schematic of excimer laser writing of optical fibre gratings [404]...

James, S. W. Tatam, R. P., Optical fibre long period grating sensors characteristics and application, Meas. Sci. Technol. 2003, 14, R49 R61... 

Brakel A (2004) Sensing characteristics of an optical fibre long-period grating Michelson refractometer. Ph.D. thesis, Rand Afrikaans University, p 317... 

Falciai R, Mignani AG, Vannini A (1998) Solution concentration measurements by means of optical fibre long-period gratings. Proc SPIE 3483 95-98... 

Those based on the fluorescence lifetime, rather than intensity (e.g. the Ipitek system), allow one to avoid problems of light loss and other factors that could affect calibration, as discussed above. Assessment of tilted Bragg gratings and long-period gratings on optical fibres has shown them to be a probe of cure of the resin as well as being both temperature- and strain-sensitive (Buggy et al, 2007). The complexity of the response of these and fibre-optics based Fabry-Perot interferometers to strain, temperature and refractive index makes it necessary to employ combinations of sensors if measurements of all of these properties are required separately. 

Many portable instruments have been made possible by the use of clever designs incorporating smaller components, for example optical fibres, light emitting diodes (LEDs), liquid crystal displays (LCDs) and miniature gratings for use in spectrometers, each of which are discussed below. These developments, amongst others, have contributed immensely to the development of the whole area of portable analytical instruments. They have seen particular use in portable electrochemical and spectrometric instruments. 

UV-Vis spectrometers have become much smaller in recent years due, in part, to the availability of hbre optics and very small grating monochromators. Miniature spectrometers have been available commercially since the 1990s. These spectrometers are often devised so that they can be interfaced to the sample and source via optical fibres. This enables difficult locations to be accessed, analytes of interest to be measured in the field and in-process and biological measurements to be taken. Some of these mini UV-Vis-NIR spectrometers can be nsed both in the laboratory and outside the laboratory for field testing. 

As mentioned earlier, optical fibres with Bragg gratings can also be applied as pressure and strain sensors. When these fibres are integrated into a mattress or bed sheet, they will be deformed as soon as pressure is exerted on them. The deformation will cause proportional changes in the Bragg wavelength and, hence, the movement can be tracked (Dziuda and Skibniewski, 2014). 

Kuang KSC, Kenny R, Whelan MP, Cantwell WJ, ChaUcer PR. Residual strain measurement and impact response of optical fibre Bragg grating sensors in fibre metal laminates. Smart Mater Struct 2001 10(2) 338—46. http //dx.doi.org/10.1088/0964-1726/10/2/321. 

A stress field applied transversely to the grating modifies the structure of the previously isotropic optical fibre, generating two perpendicular directions with different indices of refraction. For a single Bragg grating spacing... 

Wehrle, G., Nohama, P., Jose Kalinowski, H., Ignacio Torres, P., Valente, L.C.G., 2001. A fibre optic Bragg grating strain sensor for monitoring ventilatory movements. Measurement Science and Technology 12 (7), 805. 

Kuang K S C and Cantwell W J (2003), The use of conventional optical fibres and fibre Bragg gratings for damage detection in advanced composite structures - a review , ApplMech Rev, 56, 493-513. doi 10.1115/1.1582883... 

James, S.W. and Tatam, R.P. Optical fibre long-period grating sensors characteristics and application. Meas. Sci. Technol. 14(2003), pp. R49-R61 Farahi, F. Simultaneous Measurement of Strain and Temperature Using Fiber Grating Sensors. Proc. 11th Eng. Mechanics Conf. Fort Lauderdale, Conf. vol. 1 (1996), 351-354... 

Krebber, K. Habel, W.R., et al. Fiber Bragg grating sensors for monitoring of wind turbine blades. 17th Int. Conf on Optical Fibre Sensors (OFS-17), Bruges, Belgium, SPIEl-Vol. 5855 (2005), pp. 1036-1039... 

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