Research On Wavelength Switchable Erbium Doped Fiber Laser

Laser is one of the major scientific and technological inventions in the 20 th century, fiber laser has advantages of good beam quality, simple structure, low cost, good heat dissipation, high coupling efficiency with optical fiber component and immunity to electromagnetic interference, it becomes the most promising laser source. With the rapid development of wavelength division multiplexing optical network, the application of fixed wavelength fiber laser is limited, fiber laser with the function of wavelength switchability shows potential application value in optical add and drop, optical network routing, optical fiber sensing and optical instruments testing, it has attracted sustained interest of scientific researchers.The thesis mainly focus on wavelength switchable erbium doped fiber laser, the following works have been accomplished:1. The development process and research significance of fiber laser were introduced, the key problems to realize the function of wavelength switchability for erbium doped fiber laser and the latest research progress of wavelength switchable fiber laser at home and abroad were summarized.2. The basic theory of fiber laser has been studied, mainly including lasing principle of fiber laser and filtering principle of fiber filter. The transmission functions of Sagnac filter, multimode interference(MMI) filter and birefringent filter were deviated, the transmission spectrum of the three fiber filters were simulated, and their structural characteristic and filtering characteristic were compared.3. The simulation analysis of the filtering characteristic for MMI filter and birefringent filter have been carried out, respectively. The impact factors of filtering characteristic for MMI filter were analyzed based on multimode interference principle, including the core radius, numerical aperture of input or output single mode fiber and the core radius, core index, length of multimode fiber. The impact factors of filtering characteristic for birefringent filter were analyzed based on birefringence principle, including the birefringence, length of polarization maintaining fiber(PMF), the angle between the slow axis of PMF and polarization direction of polarizer, the phase difference between fast axis and slow axis caused by polarization controller(PC), the angle between the slow axis of PC and polarization direction of polarizer.4. The experimental research on the filtering characteristic of fiber filters has been carried out, MMI filter or birefringent filter is used as the key filtering component of fiber laser, and their filtering performance was tested in the experiment, respectively. A wavelength switchable erbium doped fiber laser based on multimode interference filter and birefringent filter was proposed and demonstrated, the filtering characteristic for the cascaded fiber filter was analyzed in the simulation. The experimental results indicates that the proposed laser could switch to output single-, dual-, triple- and quadruple-wavelength, side-mode suppression ratios(SMSRs) of lasing wavelengths are more than 40 d B, and wavelength fluctuations are less than 0.1nm during a period of 1h.