Study On Thermal Effect In 2?m High Power Thulium-Doped Fiber Laser

The thermal effect suppression of thulium-doped fiber laser?TDFL?is of great significance to increase the output power.At present,the 2?m band laser has been widely used in various important fields such as optical communication,military science and medical treatment.And the requirements for the laser output power is also getting higher and higher.However,the thermal effect generated when acquiring a high-power2?m band laser will be more serious when the 793 nm laser is used as the pump source,due to the spectral characteristics of thulium ions.Here,the main research goals of this paper are to reduce the thermal effect of TDFL while ensuring the output performance of the laser,and to reduce the working temperature of TDFL by optimizing the parameters that affect the fiber temperature and performance and setting the pump scheme.The main contents of this article are as follows:?1?The theoretical model based on the ³H₆?³H₄ pumping scheme is established.The output power and temperature distribution of the laser are numerically calculated when the forward pumping is exerted,and the effects of the parameters,such as doped ion concentration,cross-relaxation coefficient,fiber size,and convective heat transfer coefficient,on laser output performance and temperature distribution are analyzed.Also,practical suggestions are given for parameter selection compatible with the current optical fiber technology.?2?By equivalently replacing the multi-point boundary equation with a two-point boundary equation,the output power and temperature distribution of the laser under double-end pumping and segment pumping are obtained.When the total pump power is1000W,the maximum temperature when the TDFL works in forward pumping,double-end pumping,and segmented pumping modes are 683.21?,360.71?,and173.29?,respectively,which shows the advantages of the segmented pumping method in temperature management.Taking the 5-stage pumping method as an example,the TDFL functions properly after setting the optimal parameters.The slope efficiency is27.6%,the maximum temperature is 100.28?,the minimum temperature is 76.45?,and the temperature difference is 23.83?.Finally,the genetic algorithm is used to optimize the segmented pump power and fiber length at the same time.The slope efficiency is 29.45%,the maximum temperature in the fiber is 86.28?,and the maximum temperature difference between the fiber segments is 1.97?.Compared with results before optimization,the slope efficiency is increased by 1.85%,the maximum operating temperature of the optical fiber is reduced by 14?,and the maximum temperature difference between the segments is reduced by 21.8?,achieving uniform temperature distribution and reducing the maximum operating temperature while maintaining the laser output performance.?3?A three-stage cascade pumping scheme including three wavelength conversions is designed.The specific scheme is to obtain the signal light of 1900nm wavelength employing the pump source of 793nm,then use the pump source of 1900nm wavelength to obtain the signal light of 1940nm wavelength,and finally use the pump source of1940nm to obtain the signal light of 2020nm wavelength.The heat generation is reduced by reducing the quantum loss when the pump source is converted to the signal light,and also the heat is dispersed in the three-stage pump structure.The maximum power of the output signal light is 134W,4273W,6517W under the premise that the pumps at all levels will not damage the optical fiber,which theoretically proves that this structure will greatly increase the output power of TDFL.