Fibre-optic sensing applications of a pair of long-period fibre gratings

Abstract

We will discuss fibre-optic sensing applications with high resolution and sensitivity that are based on a pair of long-period fibre gratings (LPFGs) characterized by a fine interference fringe pattern and a narrow bandwidth. The dependence of the shift in resonance wavelength and change of peak depth of a pair of LPFGs pair on changes in the external environment such as the bending curvature, transverse load and surrounding index are investigated experimentally. The temperature sensitivity of the LPFGs was suppressed to 0.002 nm °C-1 in order to reduce the effect of temperature on the performance of the sensor.

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

“…However, although the use of such devices is advantageous, its use as a sensing element is limited by the relatively large rejection bandwidth (~10 nm) which does not provide a good resolution. In this context, several schemes for refractive index sensing based on LPGs have already been proposed Han et al, 2001). …”

“…LPG pairs have shown high resolution to refractive index measurement compared to the use of a single LPG (Han et al, 2001;Zhang et al, 2005). The advantage of using a LPGP sensor relies upon its principle of operation, where the coupled core and cladding modes from the first LPG combine again at the second matched LPG to form interference fringes.…”

“…The fine interference fringes in the transmission spectrum of the pair of LPGs can enhance the resolution and the sensitivity of measurement. The narrower bandwidth of the fringe facilitates greater resolution in the measurement of the wavelength than is possible with conventional LPGs (Han et al, 2001). The in fibre-Michelson interferometer was proposed and studied by Swart (Swart, 2004).…”

Fiber‐Optic Aqueous Dipping Sensor Based on Coaxial‐Michelson Modal Interferometers

“…Here, we are particularly interested in chemical sensor applications [2], more specifically in refractive index measurements of aqueous solutions. The use of a matched pair of LPG defining an in-line modal interferometer with a coaxial-Mach-Zehnder configuration has been investigated [3] for temperature and strain measurements [4] as well as for chemical applications [5]; this interferometric structure exhibits an enhanced sensitivity to the physical and chemical properties of the surrounding media.…”

Hydrogen Sensor Based on A Palladium-Coated Long-Period Fiber Grating Pair

“…On the other hand, the long-period fiber grating (LPG), which causes coupling between the fundamental core mode and cladding modes [10], can be an attractive alternative to improve the weak points of prior works. It is expected that the use of cladding modes coupled by an LPG results in a higher sensitivity to external perturbations than the FBG does [11], because the cladding mode encounters the environmental change directly. Furthermore, the fabrication process is relatively simple because any other treatments like etching or tapering are not necessary.…”