Study On Long Period Fiber Grating And Fiber-optic Sensors

Since the first optical fiber was fabricated, the fiber based sensing technology gradually becomes an important part in sensing technology. Fiber-optic sensors have attracted lots of attention by academic committee and industrial committee due to their intriguing properties, such as safe, immune to electromagnetic interference, suitable for remote monitoring and sever environment, et al. Nowadays, research on optical fiber sensing technology can be primarily classified into two aspects:First, the research on processing technic as the aim of reducing costs and realizing mass production; second, to improving the response sensitivity of fiber-optic sensors to external environmental parameters.The development of optical fiber communications and sensing devices are greatly boosted by the optical lithography that introduced from IC to fabrication of optical fiber devices. This thesis mainly focuses on the researches that fabricating long period amplitude mask by optical lithography. Meanwhile, all-fiber Mach-Zehnder temperature sensor based on inter-modal interference is studied.The first chapter introduces the history of the development of optical lithography, the latest development and application at home and abroad, the resist and its classification, and introduces several major types of lithography.The second chapter introduces the classification of optical fiber gratings. Secondly, two coating photo-resist methods are proposed, resolve the air bubble and embossment, and compare both methods. Next, the method that uses RZJ-304-25positive photo-resist to process long-period fiber grating is introduced. Finally, the effects of laser power on transmission spectrum of the long period fiber grating are demonstrated in experiment.The third chapter introduces the definition and classification of the coating technology. In the experiment, the fiber is coated in evaporation coating machine. Uniform coating coats on the aluminum surface. After exposure and development, photo-resist ring array(PRA) is successfully fabricated on the surface of the aluminum, and uses PRA as an anti-corrosion layer when etches the structure. Finally, aluminum ring arrays are fabricated on the fiber surface, and as amplitude mask to write long period. The fourth chapter introduces the coupled-mode theory of long period fiber grating, and compared the transmission spectra of photo-resist mask and Al mask. We analyze the causes of differences of the two spectra according to the refractive index modulation theory.The fifth chapter introduces the MZI based on thin core photosensitive fiber. According to numerical simulations, larger extinction ratio can be achieved by optimizing the structural parameters. The temperature response of sensors has been studied in the experiment, and the impact of its interference length and bending characteristics on temperature sensitivity are also analyzed and discussed. According to the experimental results, temperature sensitivity up to116pm/℃can be obtained.The sixth chapter summarizes the work, lists some questions in the experiment, and proposes some suggestions to improve work.