Fiber Grating Sensors And Applications Of Fiber Grating-based Lasers

Fiber gratings, as key passive fiber components, have received great research interest both academically and industrially because of their widely applications in fiber sensors, microwave photonics, and optical fiber communications, etc. This thesis mainly focuses on the study of fiber grating sensors and their interrogating and multiplexing technology, fiber Bragg grating based distributed Bragg reflector fiber lasers and their applications in sensing and microwave generation.Firstly, a brief overview of the background and evolution of fiber grating technology is given. Fiber grating sensing technology and recent research topics in this area are introduced. And the applications of fiber grating-based lasers are also summarized.Then, a brief introduction on the physical model and basic analysis tools of fiber gratings is given, including grating diffraction, coupled-mode theory and transfer matrix method. Several kinds fiber gratings in common use are introduced and their typical spectra are given with simulation results. The basic techniques for fiber gratings fabrication are summarized and the fabrication system used in this thesis is introduced.After that, two novel designs of fiber grating sensors are proposed and experimentally demonstrated. A fiber Bragg grating (FBG) Fabry-Perot based fiber sensor with ultrahigh resolution is studied and low cost interrogation with fast speed is achieved by employing a tunable single-longitudinal-mode semiconductor laser diode; then, the cladding modes recoupling between tilted FBGs (TFBGs) and long period gratings (LPGs) are investigated and a vibration sensor is achieved based on hybrid LPG-TFBG.Then, the interrogating and multiplexing techniques of FBG sensors are studied. Interrogating and multiplexing of FBG sensors with different topology based on optical low-coherent reflectometry is demonstrated. A multi-parameter FBG sensing network with over 40 FBG sensors is achieved by the combination of low-coherent multiplexing technique and spatial division multiplexing technique. And experiments on methane concentration, temperature and strain sensing are carried out with this sensing network. A microwave photonic filter based FBG sensing system is proposed, and its interrogating and multiplexing capability is studied experimentally. FBG sensors system based on a spectrum-limited Fourier domain mode-locking fiber laser is developed. Interrogating and multiplexing of low reflective FBG sensors with the same Bragg wavelengths is demonstrated with this system. And by incorporating a Raman amplifier, long distance sensing application is achieved.Finally, short cavity distributed Bragg reflector (DBR) fiber lasers are fabricated in two different types of erbium doped fibers. The DBR fiber lasers fabricated in a thin core erbium doped fiber have very low polarization beat frequency and thus they are suitable for sensing applications. Ultrasonic hydrophone and highly sensitive bending sensor based on this kind of fiber lasers are demonstrated experimentally. Tuning of the beat frequency is achieved by additional UV side-irradiating at the laser cavity. DBR fiber lasers fabricated in a polarization maintained erbium doped fiber have very high polarization beat frequency and thus can be used for high frequency microwave signal generation. A microwave with a high frequency of 46.66 GHz is generated experimentally, which is measured at a lower frequency through frequency up/down conversion technique.