Yunshan Zhang

Concave-lens-like long-period fiber grating bidirectional high-sensitivity bending sensor.

A novel bidirectional high-sensitivity fiber-optic bending sensor based on the concave-lens-like long-period fiber grating (CLL-LPFG) is designed and demonstrated. The CLL-LPFG is composed by an array of arc-shaped grating planes, and accordingly, its refractive index modulation serves as a concave lens. As a result, the eigencladding mode of the device gets closer to the device surface than the conventional counterpart. Therefore, the proposed sensor provides a more sensitive result. The experimental results show that the bending sensitivities of the CLL-LPFG reach -32.782  nm/m-1 within the bending range of 0-2.08  m-1, which is about sixfold compared to the reported arts. The sensitivity can be potentially improved by optimizing the grating parameters, and the temperature characteristics of the CLL-LPFG can be used to manipulate the grating spectrum.

Realizing torsion detection using berry phase in an angle-chirped long-period fiber grating

We demonstrate the fabrication of an angle-chirped long-period fiber grating (ACLPFG) in a single-mode fiber via CO2 laser pulses. Because of the Berry phase introduced by the ACLPFG, the interference acquires an extra phase difference determined by the torsion of the device. By using that unique characteristic of the proposed device, a high sensitivity sine function torsion response is achieved. The torsion sensitivity is significantly improved, and the temperature crosstalk is effectively avoided by using the relative measurement technology. The torsion sensitivity is ~16 folds (~0.94 nm/ (rad/m)) higher than that of the normal long-period fiber grating (LPFG) with only ~0.006 nm/°C temperature crosstalk within the range of 25-80 °C, which is ~10 folds lower than that of the normal LPFG.

Two-dimensional microbend sensor based on long-period fiber gratings in an isosceles triangle arrangement three-core fiber

To realize the 2D microbend sensor, we design and fabricate two non-orthogonal long-period fiber gratings (LPFGs) in an isosceles triangle arrangement three-core optical fiber which is made in our lab, making an isosceles triangle arrangement three-core optical fiber. To mark two directions without crosstalk, we write two different periods of LPFG in each of the two external cores and the central core, which induces a strong asymmetric refractive index arrangement in the fiber cross section. Theoretical analysis and experimental results verify that the resonant wavelength originates from the tunneling between the LP01 core mode in the center core and the external core. In the confirmation experiments, the proposed sensor can distinguish multiple bending directions and experiences a maximum sensitivity of 3.234  nm/m-1 with a bending range of 0-0.588  m-1.

2-D Medium–High Frequency Fiber Bragg Gratings Accelerometer

A 2-D fiber Bragg grating (FBGs) accelerometer is proposed and experimentally demonstrated in this paper. The accelerometer is composed of a universal flexure hinge and two FBGs in which the FBGs are vertically attached on the surface of the hinge. The sensing characteristics of the accelerometer are analyzed theoretically. The theoretical analysis results show that the proposed device has a linear response to applied acceleration and it was confirmed by the experiments. The experimental results show that the resonant frequencies of the accelerometer are 1050/1060 Hz in the x/y direction, respectively. The accelerometer has a wide frequency response from 50 to 900 Hz and a large sensitivity ~13.1/12.0 pm/G in the x/y direction, respectively. The maximum measurable acceleration reaches 200 G and the dynamic range is 80 dB. These unique characteristics make the accelerometer as an excellent candidate in various vibration signals monitoring field.