Study On Passively Mode-Locked Ultrashort Pulse Fiber Laser

Ultrashort pulse fiber laser has potential applied value in the domain of nonlinear optics, ultrafast optics and optical communication.In the communication windows of 1550 nm, ultrashort pulse fiber laser has been great development with the maturity of Erbium-doped fiber amplifier technology. It has become an important light source technology of development and application of wavelength division multiplexing and time division multiplexing in the high-speed large-capacity long-distance optical fiber communication system. Rare earth doped fiber is often used as the gain medium of ultrashort pulse fiber laser. The fiber laser can produce order of magnitude of ultrashort femtosecond pulse output, and it can achieve all-fiber structure easily. And it also has some virtues of simple operation, compact structure, and good compatibility. In this paper we theoretically and experimentally study generating mechanism and technology of femtosecond ultrashort pulse in the femtosecond erbium-doped fiber laser. The main contents include:1. The concept, classification, characteristics and application prospects of fiber laser are reviewed and summarized. Then the mode-locking principle and method in fiber laser are expatiated, and the passively mode-locked fiber lasers are detailedly introduced.2. We experimentally study the ultrashort pulse output from an Erbium-doped fiber laser based on nonlinear polarization rotation. Then we demonstrate the direct generation of sub-100-fs pulses from an Erbium-doped ring laser using the nonlinear polarization rotation mode-locking and optimizing dispersion management in cavity. With the optimization of the cavity, a 50fs ultrashort pulse can output from the laser finally. The centre wavelength is near the 1560nm and the repetition rate is 37.8MHz. During the experimental, with the increase of pump power, carefully adjusting the polarization controller can be observed that the fiber laser output bound soliton pulses. Seven pulses output can be observed when the pump power is 610mW.There is a same separation between the adjacent pulse peaks and the spectrum is comb-like.3. We experimentally study the ultrashort pulse output from a figure-8 Erbium-doped fiber laser based on nonlinear amplifying loop mirror. The structure and nonlinear propagation properties of nonlinear optical loop mirror based on Sagnac loop are theoretically analyzed. Then we set up a figure-8 Erbium-doped fiber laser and rationally design the cavity structure. The fiber laser uses the passive mode-locking theory of nonlinear devices dependent on the strength of input pulse to generate the femtosecond ultrashort pulse output. The width of pulse is 177fs, the centre wavelength is near the 1560nm, the width of spectrum is 16nm, the repetition rate is 19.7MHz and the output power is 12.4mW.