Optical fiber sensors based on fiber gratings have been widely studied due to its compact in size and immunity to EMI. Long period fiber gratings (LPFGs) usually hold a higher sensitivity compared with other types of fiber gratings. However, previously reported LPFGs have a typical period ranging from 100 microns to 1000 microns. LPFGs with a smaller period are rarely investigated.
Under the supervision of Prof. Xuewen Shu, Fangcheng Shen (PhD student) from Wuhan National Laboratory studied the LPFG with a period of only 25 microns. Compared with normal LPFGs, the small period LPFG exhibits unique polarization dependent dual-peak pairs, and has a higher sensitivity to surrounding refractive index and a smaller temperature cross-sensitivity. The bandwidth of the transmission dips in the small period LPFG is significantly reduced, enabling a high resolution sensing. Moreover, the grating period is so small that Bragg resonance can also be seen, which can serve as a monitor to other perturbation to realize dual parameter sensing.
This work“Small-period long-period fiber grating with improved refractive index sensitivity and dual-parameter sensing ability”was published on Optics Letters, V. 42, N. 2, 199 (2017).
In addition, the same group also reported the simulation work on fast-axis instability in mode-locked fiber laser, which was published on Opt. Express V.25, N.2, 1131-1141 (2017) with title “Numerical simulations of fast-axis instability of vector solitons in mode-locked fiber lasers”.
(a) Transmission spectrum of the small period LPFG; (b) Bragg resonance in transmission; (c) Bragg reflection.
Response of the small period LPFG to surrounding refractive index (left) and temperature (right)