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The study of temperature measurement based on the transmission of fixed wavelengths for helical long-period grating

Bai Yunfeng, He Zelong, Dang Suihu

Optica Applicata

2022

Vol. 52, nr 1

129--137

This research involves a fixed wavelength and dual-wavelength ratio temperature measurement for helical long-period grating. There are two resonant dips near 1475 and 1520 nm, with the pitch length 782 μm. The temperature sensitivity of resonance wavelengths is about 0.06 nm/°C. Both theoretical simulation and experiment results show that the transmission of a fixed wavelength linearly changes with the temperature. It has a high application value for measuring temperature. Besides, the dual-wavelength ratio is studied to eliminate the influence of light source. The temperature sensitivity of transmission intensity ratio of I1469.6nm/I0 and I1469.6nm/I1526.5nm are about 1.0076/°C and 0.0155/°C, respectively, so the dual-wavelength ratio is more practical. And the 0.0155 times intensity change could be much more easily measured than the 0.06 nm wavelength change for each degree Celsius. So the dual-wavelength ratio of the helical long-period gratings is very suitable for temperature sensors.

Helically twisted long-period fiber gratings of YOFC single-mode fiber with optical fiber welding machine

Bai Yunfeng, He Zelong, Bai Jiyuan, Dang Suihu

Optica Applicata

2021

Vol. 51, nr 3

407--413

The single-mode fiber provided by YOFC inc is employed for spiral processing by commercial welding machine. It can clearly see the periods structure under the light, but there is no obvious deformation of the fiber core, cladding and surface morphology under a microscope. There is an obvious resonant peak near 1560 nm, half peak width is about 25 nm, the depth of the resonant peak closed to –26 dB, when the period is about 411 μm. It agrees with theoretical calculation results according to the long-period fiber grating coupled-mode theory. The resonance wavelength is caused by coupling between the fundamental mode and the LP14 mode. The responsivities of the helically twisted long-period fiber gratings (H-LPFG) for the temperature is measured, the resonance wavelength is linear with temperature, the slope is 86 pm/°C. Because it is easy to inscribe by commercial welding machine, and has a strong resonance peak, it has potential applications as the temperature sensor.