A new in-line Mach-Zehnder interferometer （MZI） sensor consisting of a stub of multi-mode fiber and an up-taper was proposed and demonstrated. Temperature measurement can be carried out by detecting wavelength shift. Dependency of sensitivity on interferometer length and dip wavelength was discussed. Experimental results showed a maximum temperature sensitivity of 113.6pm/℃ can be achieved, which is superior to most fiber temperature sensors based on in-line MZIs within the range from 20℃ to 80℃, also a good mechanical strength can be obtained. The proposed sensor is a good candidate for temperature measurement, due to the advantages of simple structure, easy fabrication, cost- effective and high sensitivity.
A theoretical introduction of saturable absorber based on standing-wave saturation effects as a transient fiber Bragg grating （FBG） was presented. The central wavelength of the transient FBG was located in 2 μm. The factors affecting the bandwidth and the reflectivity of the transient FBG were analyzed. The linewidth and reflectiv- ity as the function of doped fiber length and doping concentration were correspondingly simulated by Matlab software. It was found that the larger the doping concentration and the fiber length were, the smaller the bandwidth was. These results suggest that the performance of the transient FBG can be optimized by choosing the appropriate length of doped fiber and the larger doping concentration, which can be used as a reference for the narrow-linewidth fiber laser around 2 μm.
