Long period fibre gratings for structural bend sensing

Fibre Sensing System Based on Long-Period Gratings for Monitoring Aqueous Environments

“…Lee et al (Lee et al, 1997) demonstrated a new analysis method to determine the spectral shift of an LPG as a function of refractive index of the medium. The change of this parameter with the wavelength of the LPG attenuation band was presented by Patrick (Patrick et al, 1998a). As previously mentioned, the sensitivity of the sensor to external refractive index change can be enhanced by decreasing its cladding diameter by chemical etching of the optical fiber (James & Tatam, 2003).…”

“…Since the first demonstration of LPGs by writing the grating with UV laser light through an amplitude mask in 1996 (Vengsarkar et al, 1996a), several methods have been developed to fabricate theses structures. The most widely used method is the exposition of the photosensitive optical fibres to UV light through an amplitude mask, phase mask or by interferometry (Bhatia & Vengsarkar, 1996;1998aErdogan, 1997a). In this case, the mechanism responsible for the refractive index change is related with the formation of Germania-associated defects and the gratings can be written using light with wavelengths between 193 and 355 nm (Bhatia & Vengsarkar, 1996;Zanlorensi et al, 2009).…”

“…In optical communication systems, LPGs are applied as gain equalizing filters, wavelength selective devices, band-pass and band rejection filters and wavelength tunable add/drop multiplexers (Vengsarkar et al, 1996a(Vengsarkar et al, , 1996bDong et al, 2009). In the field of sensing systems, they can be applied as structural bend sensors, temperature sensors, axial strain sensors, refractive index sensors and biochemical optical sensors (Patrick et al, 1998a;Bhatia, 1999;Falciai et al, 2001). …”

Simultaneous measurement of one dimensional bending and temperature based on Mach-Zehnder interferometer

“…Fiber optic sensors have got a growing interest due to their well-known superior advantages over conventional sensors, such as compact and integrated structure, immunity to electromagnetic interference, high sensitivity, in situ measurements, and potentially low cost [1,2]. Up to now, the curvature characteristics of fiber sensors have been studied in many works, for example, fiber grating-based sensors using the long period fiber grating (LPFG) [1], fiber Bragg grating (FBG) [2], tilted FBG [3], Mach-Zehnder interferometers (MZIs) based on fiber lateral-offset splicing [4], and two identical fused fiber tapers [5] or multimode fiber combined with an LPFG [6]. Usually, the fabricating process of the grating-based curvature sensors is relatively complicated and high power laser is usually needed [2,6].…”

Characterisation of femtosecond laser inscribed long period gratings in photonic crystal fibre

“…Long period gratings are currently the subject of considerable research interest due to their potential applications as filters and as sensing devices [3]. This study of the LPG attenuation bands has yielded many potential applications in the field of sensing through the dependence of the position of the attenuation bands on strain (ε), temperature (T), the refractive index of the surrounding medium (ns) and bending [4][5][6][7][8][9][10][11]. The spectral shift of the attenuation band arises from the phase matching condition of the LPG [3].…”