Design And Development Of High-power Output End Caps For Fiber Lasers

With the continuous development of optical fiber manufacturing technology and laser structure the output power of fiber laser is increasing,several kilowatts and ten-thousand watts fiber lasers have been used in many fields such as industrial processing and military field.The protection of the output end is the key to the safety and stability of the fiber laser.At present,the optical fiber end cap has been mainly used as the output end of high power optical fiber laser.The end cup is usually a fused quartz block with a size much larger than the optical fiber,which is connected with the laser output fiber by means of fusion.In the process of laser transmission,the laser beam is expanded through end cup so as to reduce the power density of the laser output surface and protect output end of laser.In the research of high power optical fiber end cap,the positioning and cooling of end cap are two difficult problems.On the one hand,in practical applications,the optical fiber end cap is often matched with the collimator to obtain a laser beam that is nearly collimator,and the relative position deviation between the optical fiber end cap and collimator will leads to the bad collimator and the bad beam quality of the emitted laser.On the other hand,when the fiber laser outputs high-power laser for a long time,the heat energy absorbed by the end cap accumulates continuously in the end cap,resulting in the thermal deformation and even thermal damage of the end cap,which further leads to the damage of the fiber laser.Therefore,in order to ensure the good collimation and beam quality of output laser and the safety of the optical fiber laser,the positioning and cooling of the optical fiber end cap are the key problems which must be solved.In this paper,based on the laser transmission theory,aberration theory and beam quality measurement principle,the influence of the positioning deviation of the end cap on collimation and beam quality of the laser beam are analyzed.And a device has been designed to judge the accuracy of end cap positioning by measuring the beam quality and waist position of output laser.According to the theory of heat conduction and thermal stress,the temperature field and thermal stress distribution of the end cap have been simulated when the end cap transmits highpower continuous laser for a long time,and the heat dissipation scheme of end cap has been designed and verified by experiments.In this paper,the components of the end cap have been designed and tested.The result of the testing of the laser collimation and beam quality proves that the self-developed end cap has been equivalent to the international leading optical fiber end cap in laser collimation and beam quality.In order to verify the high power carrying capacity of self-developed end cap,a 500 W and 1000 W long time light output test and a 5k W short time light output test have been conducted successively.The temperature rise of end cap was within the range required by industrial applications.