The Investigation Of The Polarization Dynamics Based On Continuous Wave Fiber Laser And Femtosecond Fiber Amplifier

Since the born of fiber laser, it has attracted lots of investigators' attention for its irreplaceable advantages, such as compactness, good heat dissipation, high degree of integration and high environment stability. However, different from the traditional solid laser based on crystal, the lasing polarization dynamic of fiber laser is far more complicate, and has a great impact on the operational status of fiber laser. This thesis focuses on the inherent polarization lasing dynamic of continuous wave(CW) fiber laser oscillator and pulsed amplifiers with three different kinds of gain fibers, respectively. The pulse dynamics of the polarizing photonics crystal fiber(PCF) femtosecond amplifier with different pumping schemes are investigated by numerical simulation and experiment. The main contents can be summarized as following:1. A CW fiber laser testing system is built, in which the lasing polarization dynamics of three kinds of gain fibers are investigated. The results show that there is a critical length to maintain polarization in the polarizing PCF. It can remain the laser output as same as it is designed. Otherwise, the polarization status of the laser emitted from the fiber will depend on the polarization direction of the incident laser. For the polarization maintained(PM) double cladding large mode area(LMA) fiber, the optimal polarization maintained ability is when the linear polarization of the incident is in along with one of the two axes of the fiber. Furthermore, the higher the pumping power, the better the polarization maintained ability is. For the non-polarization maintained LMA fiber, despite there is not polarization control element in it, polarization status of the laser emitted from it is distinctly depended on the incident laser's polarization status and pump power.2. A pulsed fiber laser amplification testing system is built, in which the pulse polarization dynamics of three kinds of gain fibers are investigated. The results show that the polarization dynamics of the polarizing PCF amplifier is almost the same as that of the CW fiber oscillator. Compared the case between the CW fiber oscillator and the pulsed amplifier with the same PM double cladding LMA gain fiber, the circular polarization degree of the amplified pulses is not only lower than that of the CW fiber laser under the same pump power, but also decrease with the pump power's increasing. The origin can be attributed to the nonlinear phase shift during the amplification. Moreover, the polarization dynamics of the pulsed amplifier with the non-polarization maintained LMA fiber is also different from that of the CW fiber oscillator.3. Keeping the polarization direction of the seed pulse along with the polarization maintained direction of gain fiber, the pulse evolution dynamics in the polarizing PCF femtosecond amplifier under different pumping schemes is studied. On the other hand, a corresponding numerical simulation is achieved, and the results are in good agreement with the experimental results. Consequently, the backward pumping scheme is superior to the forward pump scheme for the soliton pulse amplifier, due to the less nonlinear accumulation.