Research On Novel Fiber Lasers And High Sensitive Fiber-Optic Sensors

In the past decades,fiber lasers have been rapidly developed and applied in vast areas such as optics communication,laser beam machining and fiber-optic sensing. Due to high power output and high beam quality of ytterbium-doped fiber laser,fiber lasers are getting more popular in laser beam machining applications as light source. Also,with the advantage of narrow line-width output,fiber lasers have become the essential light sources in fiber-optic sensing systems.They significantly increase the sensitivity of the fiber sensor,especially in the fiber Bragg grating sensing systems which provide lots of solutions to micro-strain and vibration sensing application.In thesis,experimental researches devoted to erbium-doped fiber laser and ytterbium-doped fiber ring lasers were carried out.A short-cavity fiber laser utilizing a fiber Bragg grating inscribed into a piece of polarization-maintaining optical fiber as the output coupler was successfully developed too.The laser output performance was investigated for its wavelength stability.Also,fiber-optic sensing system constructed with fiber Bragg grating and distributed feedback semiconductor laser was developed.The main works are listed as follows:First,a compact erbium-doped ring-shaped fiber laser has been developed by utilizing a tunable fiber Fabry-Perot filter as the tuning element.The performance of the ring-shaped fiber laser configured with a piece of 500ppm concentration erbium-doped fiber was investigated for its power output,line-width and wavelength tunability.Moreover,the performance of the ring-shaped fiber laser configured with a piece of 8000ppm high-concentration erbium-doped fiber was investigated for its larger wavelength tuning range from 1513nm to 1614nm coveting both C-band region and L-band region.Also,a ring-shaped all fiberized tunable ytterbium-doped fiber ring laser with tuning range over 20 nm has been developed by using a fiber Mach-Zenhder interferometer as an intra-cavity filter.Its wavelength tuning was achieved by changing the optical length difference between two interferometer arms. Second,single-frequency linear short-cavity fiber laser features the advantage of narrow line-width output,and thus can be an essential laser source in fiber Bragg grating sensing systems.The precise temperature control over linear cavity can be easily achieved to obtain stable and tunable laser frequency output.In our experiments,a single frequency linear short-cavity fiber laser utilizing a piece of high concentration erbium-doped fiber was obtained.The fiber laser utilized a fiber Bragg grating inscribed into a piece of polarization-maintaining optical fiber as the output coupler to ensure stable single frequency laser output.Laser frequency stability was measured to be less than 3pm over 10 minutesAt last,a fiber Fabry-Perot cavity was fabricated by inscribing two fiber Bragg gratings in hydrogen-loaded single mode fiber.A fiber Bragg grating sensing system based on PDH frequency locking scheme was fabricated using fiber Fabry-Perot cavity and distributed feedback semiconductor laser.The experimental results indicate that it has high vibration sensibility from 800Hz to 6kHz with 20dB signal-to-noise ratio.The limitation to system sensitivity induced by laser line-width was analyzed.The result showed that the sensitivity of fiber Bragg grating sensing system can be greatly improved by utilizing a single-frequency linear short-cavity erbium-doped fiber laser.