2μm Pulse Fiber Laser Based On The Nonlinear Polarization Evolution Technique

The2μm pulse fiber lasers as the eye-safe band have a wide range of applications in thecivilian and military fields, such as the laser medical, materials processing, pollution control,laser radar, mid-infrared supercontinuum et al. The reported2μm pulse fiber laser mainlybased on the actively modulation technique or the saturable absorber effect of grapheme,carbon nanotubes, SESAM et al. However, the actively modulation always contain the bulkelements which make the laser system complicated and easy to be influenced by externaleviroment. The passively modulation which based on the saturable absorber effect is hard toachieve high pulse energy due to the low optical damage threshod of the materials.Thenonlinear polarization evolution (NPE) technique can also be used to achieve the2μm pulselaser as its artificial saturable absorber effect. And it has the structure advantages of all-fiber,low cost, simple and strong anti-interference performance.This dissertation using our research institute self-developed highly Tm3+-dopedgermanate glass fiber as the2μm pulse fiber laser gain medium, which net gain coefficient is2.3dB/cm. Based on the all-fiber NPE technique, we researched the2μm Q-switching,noise-like and soliton pulse fiber lasers as following issues:1. Achieved the stable all-fiber2μm Q-switched pulse fiber laser, which average outputpower fluctuation is less than±1.5%. Combining the experiments and theories, we analyzethe laser tunable characteristics of pulse repetition frequency, pulse duration and opticalspectrum based on the NPE Q-switching technique.2. A stable all-fiber2μm noise-like pulse fiber with the maximum single pulse energyof17.3nJ, corresponding3-dB spectral bandwidth of60.2nm is obtained, which based on thehigh gain, broad emission spectrum characteristics of the self-devoloped Tm3+-doped fiber.Optimizing the cavity length of the NPE noise-like mode-locked pulse fiber laser, andenhance the maximum single pulse energy to60.8nJ. Researching the optical spectrumtunability of the noise-like pulse fiber laser by experiment.3. A stable2μm soliton mode-locked pulse fiber laser was achieved at the spectralcenter wavelength of1949.7nm, corresponding3-dB spectral width is12.8nm, the limitedpulse duration is312fs, the fundamental repetition is88.1MHz and the maximum singlepulse energy is about0.67nJ. Establish the Ginzburg-Landau equation model by using thepulse tracking technique. Numerical simulation the2μm soliton mode-locked pulse fiberlaser with a fundamental repetition rate of100MHz. Simulation results show that NPEmode-locked technique can be used to achieve all-fiber2μm soliton mode-locked pulse laser with a higher fundamental repetition rate.