Research On High Power Wavelength-tunable Thulium-doped Fiber Laser

Thulium-doped fiber laser outputs eye-safe 2μm band laser,which is located in the high transmittance atmospheric window and the spectral absorption peaks of various gas molecules.So it is widely used in material processing,biomedicine,lidar,atmospheric remote sensing and other fields.The wavelength-tunable thulium-doped fiber laser with all-fiber structure has a wide tuning range and high output stability.In recent years,it has attracted extensive attention of researchers,and has been widely used in spectral analysis,wavelength division multiplexing and other fields.In this paper,the wavelength-tunable thulium-doped fiber laser is mainly studied,the fiber grating filter is used to achieve a wide range of wavelength tuning,and the output power is amplified by the main oscillation power amplification system.The main research contents of this paper are:1.The energy level structure and spectral characteristics of thulium ions were analyzed,different pumping schemes were compared and analyzed,and the theoretical model of ³H₆→³H₄ pumping scheme was established.The wavelength tuning principle of laser and different wavelength tuning technologies are introduced,and the tuning technology of fiber grating based on stress and temperature changes is theoretically analyzed.And introduced the cladding pumping technology.2.Based on the theory of thermal effects in optical fibers,a thermal model of optical fibers is established.The temperature distribution on the optical fiber cross section and the stress caused by thermal energy under different heat dissipation conditions are simulated.The metal heat sink in the cooling device is optimized to keep the surface temperature of the fiber at a level close to room temperature,when hundred watts of power is injected into the core.The influence of the thermal effect of the fiber on the laser is effectively suppressed.3.A wavelength-tunable ring cavity thulium-doped fiber laser with an all-fiber structure was designed and constructed.The wavelength tuning in the range of 1925nm to 2034nm was achieved by using a tunable filter based on fiber grating.The output spectral linewidth of the laser was about 0.5nm.The output laser has good polarization.When the pump power is 7W,the polarization extinction ratio is greater than 20d B.The thermal effect in the fiber is effectively suppressed by the laboratory water cooling system,so that the laser has good power stability,and the output power fluctuation is 0.09d B within one hour.4.The output power of the wavelength-tunable thulium-doped fiber laser is amplified by the main oscillation power amplification system.A comparative study was carried out by varying the length of the thulium-doped gain fiber in the preamplifier stage.The output laser slope efficiency is increased to 14.1%,the output power is up to 5.65W,and the polarization extinction ratio is 21.4dB.