Long-Period Fiber-Grating Temperature Sensors in Ge–B-Codoped Fibers with Temperature/Strain Discrimination

Abstract

The temperature-sensing characteristics of long-period fiber gratings were compared for different Ge-B-codoped fibers. The temperature sensitivities varied by one order of magnitude depending on the composition of the core. The temperature sensitivity varied from 0.05 to 0.5 nm/K for the same grating period of 212 mm. The sensitivities at cryogenic temperatures down to 77 K were also studied. The strain sensitivities were measured at above the room temperature. Two different loss peaks of a single long-period grating with negative temperature sensitivities and positive strain sensitivities were used to distinguish applied temperature and strain. Discrimination characteristics using a Ge-B-codoped fiber were studied for a strain of up to 4000 m".

Highly Strain-Sensitive Long-Period Grating in Hi-Bi Fiber with a Reference Fiber Bragg Grating

“…The peak 2 of the slow axis had a sensitivity of 2.4 pm/με. The strain sensitivity of 3.6 pm/με was 80 percent higher than that of an LPG in conventional 1.3-μm single-mode fiber [11] and 16 percent higher than that in Ge-B co-doped photosensitive fiber [8]. The temperature sensitivity for the peak 2 of the fast axis had the highest sensitivity of 88 pm/ ºC.…”

“…The peak 2 of the slow axis was temperature independent around the room temperature. In our previous discrimination using two coupling cladding modes [11], the longer wavelength had the higher strain and temperature sensitivities, and shorter wavelength had the lower strain and temperature sensitivities. Thus, the present results are more suitable because one is temperature sensitive and the other is strain sensitive.…”

“…It is expected that a high sensitivity is also possible with an LPG in Hi-Bi fiber using polarization dependence. Also, various schemes of strain/ temperature discrimination have been reported using two loss peaks by different coupling cladding modes [10,11], a combination of FBG/LPG [12], and an LPG in Hi-Bi fiber [3,4]. A high strain sensitivity is also suitable for strain/temperature discrimination.…”

“…Annealing at 150 ºC for 24 h was performed to stabilize the spectrum. Strain and temperature measurements were performed with a translation stage in an oven [11].…”

High Sensitivity Cryogenic Temperature Sensors Based on Arc-Induced Long-Period Fiber Gratings

“…On the other hand, it is known that long-period fiber gratings (LPFGs) possess higher temperature sensitivity, typically an order of magnitude higher for temperatures above room temperature [ 21 ]. However, research involving the use of LPFGs at cryogenic temperatures is very scarce [ 22 , 23 , 24 ], possibly due to two main factors: they need access to both sides of the fiber, and they are also very sensitive to bending. In 2015 [ 25 ], we solved the problem by using a phase-shift LPFG (PS-LPFG) working in reflection placed inside a polyamide capillary with a 1 mm inside diameter.…”