Research On Nonlinear Polarization Rotation Mode-locked Fiber Laser

Laser mode-locking technique is an important technique to generate ultra-short laser pulses, and it has broad application prospects in optical communications, terahertz technology, biomedical, military and other fields. It has important academic significance and market value to do research on various mode-locked fiber lasers because of mature technology and the advantages of small size, stable performance of fiber laser.This paper focuses on the physical mechanism and operating characteristics of nonlinear polarization rotation (NPR) mode-locked fiber laser with ring cavity, and does deep research on the theoretical analysis and numerical simulation on the effect of system parameters on the NPR mode-locked fiber laser. What’s more, built NPR mode-locked fiber laser experimental system, and gets some interesting findings. The main contents are as follows:(1) According to the basic theory of optical fiber amplifiers and fiber optics to establish a theoretical model of NPR mode-locked fiber laser with ring cavity. At the same time, establish numerical analysis model of the optical signal transmission in fiber amplifier and evolution by traveling-wave rate equation model and split-step.(2) Establish Matlab numerical simulation program for NPR mode-locked fiber laser with ring cavity. And use the numerical simulation program to do detail numerical simulation research on the formation process of mode-locked pulse and the influence of the polarization controlling on the pulse.(3) Build an experimental system of NPR mode-locked fiber laser with common EDFA, the optical fiber polarizer and a polarization controller, and obtain repetition stable mode-locked laser pulse output with frequencies of4.3MHz and1.78MHz with different length of the ring cavity. At the same time, do research on the effect of enhancing the non-linear effect of rotation by increasing cavity’s length on the mode locking threshold.(4) Build an experimental system of NPR mode-locked fiber laser with polarization maintaining EDFA and polarization and obtain mode-locked output pulse with repetition rate of1.79MHz and3dB spectral width of0.3nm. It was found that by adjusting the polarization state of the controller can realize center wavelength of the mode-locked pulse tuning within the range of4.5nm.