Sensitivity-enhanced optical temperature sensor with cascaded LPFGs

Abstract

We propose a new structure of optical fiber temperature sensor with cascaded long-period fiber gratings (LPFGs) and investigate the temperature dependent loss of cascaded LFPGs. Each of the cascaded LPFGs has the same resonance wavelength with the same temperature change, because the cascaded LPFGs are made of a heat-shrinkable tube and a screw. The total resonance loss of proposed cascaded LPFGs shows higher temperature sensitivity than that of a single LPFG. The thermal coefficient of 4-cascaded LPFG also shows more than 4 times larger than that of a single one.

Mode recoupling between core and cladding modes of cascaded-LPFGs fabricated with heat-shrinkable tube employing a thin confinement layer

“…2(a) and (e)∼(h) that the attenuation bandwidth of cascaded-LPFGs broadens compared with a united-LPFG as the cladding mode loss increases. The measured spectrum of the united-LPFG fabricated with a heat-shrinkable tube shows the similar one calculated for the high cladding mode loss [8,10]. Therefore, we clarified that the mode recoupling of the conventional cascaded-LPFG fabricated with the heat-shrinkable tube cannot occur due to the high cladding mode loss, and that the cladding mode loss is an important factor for controlling the transmittance of the cascaded-LPFG.…”

“…It can be used as the sensor which doesn't detect the changes in the physical parameters at the LPFGs, but in the fiber between the LPFGs. However, mode recoupling between cladding and core modes did not occur when our LPFGs fabricated via heat-shrinkable tube were cascaded [10].…”

“…To reduce the cladding mode loss, a thin metallic layer is employed. Using a transfer-matrix model, we investigate the transmittance of the cascaded-LPFG, focusing on the cladding mode loss at the LPFG [9], and clarify that the mode recoupling of the conventional cascaded-LPFG fabricated with heat-shrinkable tube [10] does not occur due to high cladding mode losses. Fig.…”

Cladding mode loss effect on transmission characteristics of mechanically induced long‐period fiber gratings

“…Optical fiber sensors are immune to electromagnetic noise, and sensor heads do not conduct electricity; hence, excellent explosion proofness and other merits. Particularly, mechanically induced long‐period fiber gratings (MLPFGs) feature a simple structure and relatively inexpensive manufacture, while their light transmission spectra vary with MLPFG temperature, strain, external refractive index, and other parameters; a number of studies were conducted on sensor applications 1–5 . MLPFG is an optical device provided with diffraction grating formed through periodical compression so that refractive index of optical fiber periodically changes 6,7 .…”