Erbium-doped fiber laser based on femtosecond laser inscribed FBG through fiber coating for strain sensing in liquid nitrogen environment.

• This paper proposes a strain sensing system based on an erbium-doped fiber laser in liquid nitrogen environment. • The FBG is inscribed through polyimide coating and cladding, realized by a femtosecond laser point-by-point inscribing method. • The strain sensitivity of the sensing system is 0.890 pm/με and the linearity is 99.72 % in liquid nitrogen environment. In this paper, a strain sensing system based on an erbium-doped fiber laser in liquid nitrogen environment is proposed and experimentally verified. A fiber Bragg grating (FBG) and a Sagnac loop are used as cavity mirrors of a fiber laser. The FBG with a central wavelength of 1532.39 nm, a 3-dB linewidth of 0.61 nm, and a signal-to-noise ratio (SNR) of 9.06 dB is inscribed through polyimide coating and cladding, realized by a femtosecond laser point-by-point inscribing method. The 3-dB linewidth and SNR of the fiber laser are 0.06 nm and 36.53 dB, respectively. The measurement results show that the linear range of the measurement is from 1,000 με to 3,000 με, the strain sensitivity of the system is 0.890 pm/με and the linearity is 99.72 % in liquid nitrogen environment. [ABSTRACT FROM AUTHOR]