For diode pump fiber laser, there’s potential to achieve high power quasi-CW output by applying overshoot pulse modulation to diode, meaning that applying several times of currents to the diode to attain remarkably higher power than rated value. In this paper, we first build up the physical modal of the quasi-CW fiber laser based on time-dependent rate equations and solve them with parallelizable bidirectional method for simulation. The result shows that for square wave pump with 1kHz frequency and 500μs duration, the output peak power is about 5.1kW with 2kW forward pump and 4kW backward pump. Applying overshoot pulse modulation to 3 diodes at 976nm to pump ytterbium-doped fiber oscillator, we obtain 500Hz, 1kHz frequency and 100, 200μs duration output, respectively. With 1kHz frequency and 200μs duration pump with an average power of 192W, the average output power is 192W with 60.8% optical efficiency at 1080nm, of which the M2 beam quality is about 1.5. The output waveform shows good consistency of the pump diode with low delay between. It’s the very first time in the country to attain pulse fiber laser output by applying overshoot pulse modulation to diode to our acknowledgment.
This paper uses SeeFiberLaser simulation software to simulate and optimize a new type of double-ended output fiber laser. Using the controlled variable method, the reflectance range of the high reflectivity fiber grating is set to 50%-95%, with 5% Step, change the reflectivity of the low reflectivity fiber grating, step by 2%, respectively simulate the laser output power of different reflectivity combinations. The simulation results show that the double-ended laser output and the power can be controlled by changing the reflectivity of the fiber grating. When the reflectivity of the high-reflectivity fiber grating is 50%, and the reflectivity of the low-reflectivity fiber grating is 5%, The total output power of the forward and backward directions is the largest; when the reflectivity of the two fiber gratings are both 50%, the output power of the front and rear ends of the laser is the closest; no matter which direction the fiber grating reflectivity is increased, the output power in this direction will become lower, the output power in the other direction becomes higher and the total output power becomes lower.
At present, fiber amplifiers are generally pumped by fiber-coupled semiconductor laser with a wavelength of 915nm or 976nm. With fast development of application field, the requirement of pump injection power is becoming higher and higher, single-band pumping may not meet practical requirements in high-power fiber laser applications. The total power of the pump source can be greatly increased by combining the 915nm and 976nm pump sources with spectral bundling technology. Based on this, the gain fiber length of hybrid wavelength pumped fiber amplifiers at 915nm and 976nm was optimized under different pump power ratios. By usingSeeFiberLaser software, we investigated the relationship between pump power ratio and output power, efficiency, residual pump power, Raman power and the length of active fiber. This paper has some guiding significance for choosing the pump power ratio and gain fiber length of mixed wavelength pump fiber amplifier.
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