Highly sensitive pressure sensor based on long-period gratings written in a boron co-doped optical fiber

Abstract

The paper presents a novel pressure sensor based on long-period gratings (LPGs) written with an arc-induced method in a boron co-doped photosensitive fiber. The achieved pressure sensitivity for these gratings is at least four to eight times higher than for gratings written in other fibers which have been presented to date. The sensitivity is strongly dependent on the investigated order of modes, and for the 7th cladding mode can reach δλ/δp = 78 pm bar −1 . It was found that the incorporation of B 2 O 3 in the core of the fiber is responsible for the higher pressure sensitivity of these LPGs. This conclusion is based on consideration of variations in the elastic properties of the glass versus its composition. According to our simulations, the pressure-optic coefficient of the B/Ge-doped core of the fiber is 2.03 RIU bar −1 . The sensitivity of the structure to temperature and to external refractive index is discussed from the point of view of the possible indirect influence of these conditions on the pressure response. It is proven that the experiment was conducted in such a way that the measured pressure sensitivity was not significantly affected by variations in either the temperature or the external refractive index.

Highly sensitive pressure sensor based on cascaded long-period gratings

“…The effect can be clearly observed for each set of the CLPG resonances, and also it could be observed for a single LPG [5]. Moreover, it must be mentioned here that the cascaded LPGs have a very similar pressure sensitivity when compared to the single LPGs [4]. For the single LPG the measured pressure sensitivity reaches 0.078 nm/bar, which is comparable to the values shown here for the CLPG.…”

“…Most of them employ a Fabry-Perot resonator in the form of an extrinsic or an intrinsic sensor [1]. A number of papers have been published dealing with the use of fiber Bragg gratings (FBGs) [2] or long-period gratings (LPGs) [3,4,5,6] as the pressure-sensitive devices. Grating-based devices offer high durability due to a fact that they do not contain any moving elements and the sensing principle is typically based on pressure induced variations in optical properties of the fiber material.…”

“…Depending on composition of the fiber's core and cladding material they show various level of sensitivity [4]. The highest pressure sensitivity presented up to date in the field of gratings (up to 1 nm/bar), was observed for an LPG written in a boron co-doped fiber, where the small modulation period allows to reach the doubleresonance regime [5].…”

Pressure sensitivity of dual resonant long-period gratings written in boron co-doped optical fiber

“…Incorporating B 2 O 3 into fused silica greatly increases the pressure-optic coefficient of the silica, so that the core material has a higher pressure-optic coefficient than the cladding. This relation directly explains the positive pressure sensitivity of LPGs written in boron codoped fiber 7 .…”

“…A number of papers also deal with the use of fiber Bragg gratings (FBGs) 3,4 or long-period gratings (LPGs) 5, 6, 7 as pressure-sensitive devices. In our previous works we have reported the significant sensitivity of LPGs written with a cost-effective electric arc method in standard germanium-containing single-mode fiber (Corning SMF28) 5 , pure fused silica endless single-mode photonic crystal fiber (PCF ESM-12-01) 6 and germanium and boron (B/Ge) co-doped photosensitive fiber (Fibercore PS 1250/1500) 7 . The sensitivity of the structures was as high as 13 and 220 pm/bar for the SMF28 and PS 1250/1500 fibers, respectively 8 .…”