Research On Optimization Of 793nm Laser Pumped Thulium Doped Fiber Amplifier

Thulium-doped fiber lasers working in the eye-safe 2?m band and have important applications in radar,gas detection,and mid-infrared light source generation.It also has a good application prospect in medical,remote sensing,free space optical communication and other fields.Sufficient power and good beam quality are undoubtedly important preconditions for 2?m lasers in practical applications.This raises higher requirements for thulium-doped fiber amplifiers.In a variety of pump structures with thulium-doped fibers,the 793 nm laser pump has a high pumping efficiency,and the 793 nm high-power laser diode process is relatively mature,and is perfectly compatible with the double-clad erbium doped fiber cladding pump structure.This paper studies the optimization of thulium-doped fiber amplifier based on 793 nm laser pumping.It introduces the research status and basic working principle of thulium-doped fiber amplifier,and carries out related research on theory and experiment respectively.The specific research contents can be summarized as follows:1.Theoretical research:In the theoretical simulation of the amplifier seed source part,we simulate the effect of gain fiber length and reflective grating parameters on output power.The simulation results show that when the pump power is 6W and the gain fiber length is 3m,the seed source output power reaches the maximum.The lower the reflectivity of the rear mirror,the higher the output power.When the reflectivity of the reflective grating as the rear mirror is 10%,the output power reaches the highest.In the simulation part of the amplifier,the theoretical simulation of the gain fiber length,the different gain fiber doping concentration,pump power,signal optical power on the output characteristics is carried out.After that,the parameters of the thulium-doped fiber are selected according to the gain spectrum and the average normalized particle number.The simulation results show that the thulium-doped fiber with a length of 1m and a core diameter of 25/250 can more easily achieve high power output.2.Experimental study:A pulsed thulium-doped fiber laser centered at 1908 nm is constructed as the source.The repetition rate can be tuned from 100 kHz to 800 kHz.The duty cycle can be tuned from 20% to 80%.This fiber laser source can operate at Milli-watts level.A primary amplification structure is set up and the output power of the forward pumping structure can reach more than 1.012 W.The output characteristics of the forward,backward,and bidirectional pumping modes are compared and analyzed.The experimental results show that the forward pumping can ensure a high output power,and at the same time it has better spectral characteristics.A secondary amplification system based on large core gain fiber is set up.The temperature control of gain fiber is carried out by water cooling module.In this case,the effect of gain fiber cooling temperature on output power is studied.Fixing the laser source at 100 kHz repetition rate and 20% cycle duty,when the temperature of the water cooling module was 20°C,the output power is 4.63 W,corresponding to 19.65% slope efficiency.Decreasing the water cooling module to 10°C,the output power can reach 7.56 W and the slope efficiency can reach 32.3%.