The Research Of Temperature-Insensitive Chemical Concentration Sensor Based On Twin Bragg Grating And Fiber Grating Demodulating Technology

Fiber grating sensor can transfer information through optic signal. Compared with the traditional sensor system, the fiber grating sensor has some special characteristics such as immunity to electromagnetic interference, distributed sensoring, high precision, etc. And now it has been widely applied in optical communications, architecture, military, medicine and chemical industry and many other fields. Because of the excellent properties, optical fiber grating is a hot research spot in recent years. The present paper has done the work as follows:1. The structure and sensing mechanism of long-period fiber grating(LPFG) and fiber bragg grating(FBG) chemical sensor are introduced. The influence of reducing temperature sensitivity of LPFG and FBG chemical sensor is focused on, respectively. The temperature-insensitive LPFG and FBG chemical sensor in concentration measurement of chemical solutions are analysed. One method based twin FBG is designed by measuring the peak wavelength difference between twin FBG, which has the sensitivity of 0.096nm for change 1% concentration of sugar solutions.2. A demodulating method based on the principle of polarized-light interferometer is introduced in this paper. The novel polarization maintaining fiber loop method, which is formed by inserting a fiber polarization controller into the loop, is introduced in our experiment. We can vary the optics axis orientation by adjusting the polarization controller. Different from the conventional unbalance Mach-Zehnder interferometer, this polarization interferometer is based on the unequal refractive index ne and no. With the coupler theory and the optical waveguide theory, we got the output expression and fringe visibility expression of the unbalanced fiber Mach-Zehnder interferometer. The relationship between the fringe visibility of interferometer and polarization of input light is theoretically confirmed. The experiment results demonstrate that this system has better static state measurement performance than Mach-Zehnder interferometer and fits precision testing.3. A novel fiber grating sensor networks is introduced, which is based on wireless data transmission. The circuittopology of sensor probe and wireless chip are designed, which are demonstrated by experiments.