Research On The Pulsed Yb-doped Double-cladding Fiber Laser And Relevant Components

Due to its intrinsic characters:stability,low loss,compactness,versatility,fiber grating is widely applied in a variety of areas especially in sensing system and WDM high-speed all optical communication system.And the research on high power pulsed fiber lasers has become the international hotspot because of the advantages such as good beam quality,high efficiency,excellent heat dissipation capability and compactness.In this thesis,the main work is the research of high power pulsed fiber lasers and relevant devices.The thesis is composed of following research work: MOPA structured pulsed fiber amplifier,acousto-optic(AO) Q-switched fiber laser, fiber grating,dual-wavelength fiber laser based on a few-mode fiber Bragg grating (FMFBG).Two kinds of MOPA structured linearly polarized fiber amplifiers were demonstrated.The fiber used in both amplifiers was ytterbium-doped Panda-type polarization maintaining(PM) double clad fiber.One fiber amplifier was seeded by acousto-optic Q-switched Nd:GdVO₄ laser.When the pump power was 30.4W.stable linearly polarized average output power of 20W with associated polarization extinction ratio(PER) in excess of 14dB was obtained at a repetition rate of 40 kHz. Due to the narrow linewidth of the solid state laser,serious nonlinear effects were observed in the fiber amplifier.The other fiberized amplifier was seeded by a Q-switched fiber laser.When the pump power was 34.8W,linearly polarized single-transverse-mode pulses with average power up to 23.5W were obtained at a ropetition rate o f 40 kHz.The measured polarization extinction ratio was greater than 10dB.Because the Q-switched seed laser had larger linewidth,no serious nonlinear effect was observed.The acousto-optic(AO) Q-switched fiber laser was set up with Fabry-Perot cavity structure by applying a piece of lm-length large mode area polarization maintaining Yb fiber as the gain medium and a free-space AO Q-switch as the modulating element.Stable Q-switched short pulsed laser output was achieved with power up to 10 W and repetition rate between 20 kHz and 50 kHz.The shortest pulse duration of 33 ns was achieved at repetition rate of 20 kHz when the output power reached about 10 W.The parameters,such as the fiber length,pump power and the transmissivity of the output mirror,which affect the output power and pulse linewidth, were analyzed.A high pressure H₂ loading system was developed to enhance UV photosensitivity of optical fibers and different kinds of Bragg gratings were fabricated from singlemode,multimode,polarization maintaining fibers with phase mask method.The fiber Bragg gratings-based Fabry-Perot cavity was also made.We also demonstrated a dual-wavelength Yb-doped double-cladding fiber laser based on a FMFBG.The FMFBG was fabricated by using a single-mode fiber with a cutoff wavelength of 1230 nm.Stable dual-wavelength operation was achieved with output power up to 5.67 W under pump power of 10.7 W.The laser wavelengths were centered at 1059.12 nm and 1060.80 nm with a full width at half maximum of 37 pm and 43 pm respectively.The signal-to-noise-ratio was greater than 50 dB and the beam quality factor(M²) was about 1.9.