Investigation On NPR Passively Mode-locked Erbium-doped Fiber Laser And Adjust-free Nd: YAG Solid Laser

The dissertation is supported by the National Natural Science Foundation of China under Grant No 10476028 and military 863 pre-research Foundation. It includes two parts: Part I. Investigation on NPR passively mode-locked erbium-doped fiber laser, and Part II. Investigation on adjust-free Nd:YAG solid laser.The contents and conclusions of Part I are as follows:1. The parameters of mode-locked pulse are simulated numerically by the Master equation. We conclude that stable mode-locked pulse can form in the cavity with both positive and negative dispersion. According to coupled nonlinear Schrodinger equation, we simulate the evolvement process of pulse in the cavity and the affect on pulse width by the change of dispersion in the cavity.2. We develop NPR passively mode-locked erbium-doped fiber laser with passively dispersion cavity, and manufacture the prototypical. The laser has low threshold value of 40mW. We observe rectangular shape spectrum, the 3dB bandwidth at threshold is 14.94nm and the pulse width is 21ps. The bandwidth increases to the most value of 17.61nm with the increasing of pump power. Two and three pulses co-existing in the cavity are observed when the pump powers are 81mW and 149mW respectively. Keeping power at 149mW and adjusting PC1 and PC2, we obtain five pulses co-existing in the cavity. The variation of spectrum, pulse energy, pulse width and peak power with pump power are simulated. We analyze the mechanism of multiple-pulse operation.3. We apply the NPR passively mode-locked erbium-doped fiber laser on sub-ns high-speed analog-to-digital converter as optical resource. The influence on system performance by the wavelength response of modulator is analyzed theoretically. Using the sin signal with 4.16ns period, we carry on the time-stretch experiment, and get the stretched results of 1.96 and 2.1 times, which proves that the design idea of time stretch is feasible.The contents and conclusions of Part II are as follows:1. We analyze the characteristics of adjust-free Nd:YAG solid laser. According to simulation results we conclude that the cavity with corner cube is a little sensitive to displacement maladjustment of corner cube and is not sensitive to the angle maladjustment of output mirror. By fresnel-Kirchhoff equation, we simulate the near field facula of the cavity with corner cube, which is composed of six petals and the results correspond with experiment. We add a polarizer in the cavity and the simulated results shows that the transmissivity changes with the rotation of corner cube.2. The adjust-free passively Q-switched Nd:YAG laser is realized by use of the Cr⁴⁺:YAG crystal as passive Q-switch. The simulated results shows that the peak power, pulse energy and pulse width changes with the rotation of corner cube. The most peak power and pulse energy in experiment is 10.36MW and 174.4mJ respectively. The variation range caused by the rotation of corner cube is 1.77MW and 14.9mJ respectively. The pulse width fluctuate around 20 ns. Those correspond with theoretical results.3. We present the passive mode-locking of adjust-free Nd: YAG laser. The pulse has high modulation depth and the period is 3.3 ns. The laser can work under two states as passive mode-locking and passive Q-switching by rotating the corner cube. Electro-optical Q-switch is realized by adding a polarizer between KTP crystal and corner cube. The most pulse energy is 190mJ and the pulse width is 10.77ns.Highlights of the dissertation are as follows:1. We develop the NPR passively mode-locked erbium-doped fiber laser and validate a kind of new soliton—gain guided siliton. The rectangular shape spectrum is obtained and the results are better than that of L. M. Zhao et. al. We observe the multiple-pulse operation in the cavity for the first time.2. We apply the NPR passively mode-locked erbium-doped fiber laser on sub-ns high-speed analog-to-digital converter. Using the sin signal with 4.16ns period, we carry on the time-stretch experiment, and get the stretched results of 1.96 and 2.1 times.3. The adjust-free passively Q-switched Nd:YAG laser is realized. For the first time, we analyze the influence to the pulse by the polarization of corner cube. The most peak power and pulse energy in experiment is 10.36MW and 174.4mJ respectively. The variation range caused by the rotation of corner cube is 1.77MW and 14.9mJ respectively.4. We obtain passively mode-locked pulse of adjust-free Nd:YAG laser in experiment, which has high modulation depth and the period is 3.3 ns. We find that the laser can work under two states as passive mode-locking and passive Q-switching by rotating the corner cube. According to theoretical analyse, we know it is caused by the variation of intensity in the cavity induced by the polarization variation.