Yunhe Zhao

Mode converter based on the long-period fiber gratings written in the two-mode fiber

We demonstrated the fabrication of long period fiber gratings written in two-mode fiber as mode converter to realize the mode conversion between LP01 mode and LP11 mode with an efficiency of up to 99.9%.

High Sensitivity Twist Sensor Based on Helical Long-Period Grating Written in Two-Mode Fiber

We demonstrate the fabrication of the helical long-period grating (HLPG) in a two-mode fiber (TMF) with CO2 laser. The torsion characteristics of the helical gratings are experimentally investigated. It was found that the resonance wavelength of the TMF-HLPG linearly shifts with a twist sensitivity of 0.47 nm/(rad/m), which is an order magnitude higher than that of the conventional long-period fiber gratings (LPFGs). The temperature sensitivity of the TMF-HPFG was measured to be 23.9 pm/°C, which is one third of that of the conventional LPFGs. The proposed TMF-HLPG-based twist sensor would have a promising application for the twist monitor.

Magnetic Field Sensor Using Fiber Ring Cavity Laser Based on Magnetic Fluid

A magnetic field sensor using fiber ring cavity laser based on magnetic fluid (MF) is proposed and experimentally demonstrated. MF-coated single-mode-no-core-singlemode fiber structure is inserted in the fiber ring laser cavity, which acts as a bandpass filter and the magnetic field sensing component simultaneously. The excellent bandpass filtering with a high side-mode suppression ratio (14 dB) and small insert loss of around (-1.03 dB) is caused by the self-imaging effect. The experimental results show that the lasing wavelength shifts to blue side with the increase of external magnetic field. The magnetic field sensing sensitivity of 12.05 pm/Oe is achieved within the range of 15.9-222.32 Oe. This configuration exhibits obvious advantages in term of high visibility (~40 dB) and relative narrow 3-dB bandwidth (~0.19 nm) of the lasing output spectrum. Therefore, its Q value is more than 10 times larger than those of other reported magnetic field sensing structures.

Sensing Characteristics of Long-Period Fiber Gratings Written in Thinned Cladding Fiber

We demonstrate the fabrication of the long-period fiber gratings (LPFGs) in the thinned cladding fiber by CO2 laser and the characteristics of the gratings is experimentally investigated for the sensor application. The cladding modes are excited in the thinned cladding fiber, which is found to be highly sensitive to the surrounding index changes. A high index sensitivity of 7366.6 nm/refractive index unit (RIU) was achieved, which is much higher than that of the same order cladding mode of the common LPFGs written in the conventional single-mode fibers. In addition, the over-coupled LPFGs obtain a higher grating contrast in the index sensitive region (1.447-1.457), which is helpful for the wavelength detection. The temperature and bending sensitivities of this promising refractive index sensor were measured to be 70.85 pm/°C and 2.32 dB/

Refractive index sensitivity of long-period fiber gratings written in thinned cladding fiber by CO2 laser

\text{m}^{-1}

In-Line Mach-Zehnder Interferometer With D-Shaped Fiber Grating for Temperature-Discriminated Directional Curvature Measurement

, respectively.

Refractive Index Sensitivity of Tilted Long Period Fibre Gratings Written in Thinned Cladding Fibre

We demonstrate the fabrication of the long-period fiber gratings (LPFGs) in the thinned cladding fiber (TCF) using CO2 laser. The sensing response of the gratings to surrounding refractive index has been investigated experimentally. The LPFGs written in the TCF could be used as the high sensitive refractive index sensors.

Mode converter based on the long period fiber gratings written in two mode fiber

A high-sensitivity curvature sensing configuration is implemented by using a fiber Mach-Zehnder interferometer (MZI) with D-shaped fiber Bragg grating (FBG). A segment of D-shaped fiber is fusion spliced into a single mode fiber at both sides, and then a short FBG is inscribed in the D-shaped fiber. The fiber device yields a significant spectrum sensitivity as high as 87.7 nm/m−1 to the ultralow curvature range from 0 to 0.3 m−1 , and can distinguish the orientation of curvature experienced by the fiber as the attenuation dip producing either a blue or red wavelength shift, by virtue of the asymmetry of D-shaped fiber cladding. In addition, by tracking both resonant wavelengths of the MZI and embedded FBG, the temperature and curvature can be measured simultaneously.

Multi-channel mode converters based on in-line fiber modal interferometer

We demonstrated the fabrication of tilted long period fibre gratings written in the thinned cladding fibre by CO2 laser. The refractive index characteristics of the gratings with different tilted angles were investigated experimentally. The experimental results show that the grating with larger tilted angle has higher sensitivity to the surrounding refractive index changes.

Potential bending sensor based on small-period long-period gratings

We demonstrated the fabrication of long period fiber gratings written in two-mode fiber as mode converter to realize the mode conversion between LP01 mode and LP11 mode with an efficiency of up to 99.9%.