Research On Switchable Dual-Wavelength And Single-Longitudinal-Mode 2?m Fiber Laser

2?m fiber lasers have good potential applications in the fields of laser medicine, remote sensing guided, laser ladar, free space optical communication and so on, due to the unique characteristics of eye-safe and high absorption in liquid water. Under this framework, the novel switchable 2?m multi-wavelength fiber laser and switchable 2?m multi-wavelength single-longitudinal-mode fiber laser can improve the communication channels numbers in communication system and can make laser resource portion compact and economic in fiber sensor system. For the present, not many researches have been reported in this direction, but it has a very impressive prospect. Thus, the research towards 2?m switchable multi-wavelength single-longitudinal-mode fiber laser is significant and meaningful.This thesis is supported by the project of National Natural Science Foundation of China(project No.61290315), and is devoted to switchable multi-wavelength single-longitudinal-mode fiber laser in 2?m region. A novel switchable multi-wavelength 2?m fiber laser and a switchable multi-wavelength single-longitudinal-mode 2?m fiber laser have been proposed. The relevant mechanisms have been researched thoroughly and systematically, and the corresponding experimental results have been discussed and validated. The main achievements of this thesis are listed as follows:(1) A lot of literature research have been done towards to 2?m fiber lasers, switchable multi-wavelength 2?m fiber lasers and single-longitudinal-mode fiber lasers. The research progress and development trend of 2?m switchable multi-wavelength fiber laser and multi-wavelength single-longitudinal-mode fiber laser have been studied. This study provides an important reference for this thesis.(2)Introducing the basic knowledge of thulium and holmium co-doped fiber as active medium producing 2?m laser by 1570 nm pumping. Through the theory of longitudinal mode, line broadening and gain competition, the principle of switchable fiber laser by loss modulation has been analyzed. The concept of single longitudinal mode fiber laser has been introduced. In addition, the mechanism of unpumped fiber as saturated absorber and self-injection locking effect to suppressing linewidth and stabling single-longitudinal-mode have been analyzed. These works provide important theoretical basis for this thesis.(3)A switchable dual-wavelength fiber laser using 3×3 coupler based on the theory of common gain medium and different cavities has been demonstrate. And the switchable, tunable, and power controllable characteristics of this laser have been experimental analyzed. By adjusting the cavity losses and pump power, a dual-wavelength laser emission with controllable power has been simultaneously obtained. the dual wavelengths have a tuning range of 6.5 and 4.0 nm, with full width at half maximum of ~0.2 nm, power instability of 0.78 dB and wavelength drift of 0.08 nm are obtained.(4) Based on the mechanism of unpumped fiber as saturated absorber and self-injection locking effect to suppressing linewidth and stabling single-longitudinal-mode, a novel 2?m switchable and tunable single-longitudinal-mode fiber laser have been proposed. Dual-wavelength with power-instability of ~0.7 dB, wavelength drift of ±0.08 nm and a tuning range of 6.7 nm and 2.7 nm is obtained. Stable single-longitudinal-mode operation with linewidths of less than 9.1MHz analyzed by self-homodyne method is obtained.