Research On High Power Semiconductor Pulse Lasers Based On MOPA Structure

Ultra-short pulse lasers have the characteristics of short pulse duration,high repetition frequency,and high peak power.They have important applications in scientific research,industry,communications,medicine and other fields,and have made great contributions to the progress of human society.Semiconductor pulse lasers have become a hotspot of ultrashort pulse sources because of their series of advantages such as small size,long life,light weight,high conversion efficiency,rich wavelength,and cheap price.This thesis was focused on the scientific issue that high power and ultra-short pulse duration output of semiconductor pulse laser system based on master oscillator-power amplifier(MOPA)structure.Harmonic mode-locking operation in an external cavity tapered diode laser,the amplified spontaneous emission(ASE)was reduced in the tapered semiconductor optical amplifier(SOA),femtosecond optical pulse output with dual-pass grating compressor have been investigated.(1)An external cavity tapered harmonic mode-lock laser with a saw-tooth microstructure was designed and manufactured.The software was used to simulate the reflectivity of different saw-tooth structures,and the optimal saw-tooth structure was determined.The stable picosecond pulse trains were observed up to the third order harmonic mode locking.The mechanism behind the system was analyzed and singlepulse energy of 59 pJ with a repetition rate of 412 MHz and pulse duration of 3.9 ps was realized.(2)Aiming at the problem of amplified spontaneous emission in the amplifier,a method of manufacturing a saw-tooth structure on the side wall of the waveguide was proposed to suppress the amplified spontaneous emission.The influence of different saw-tooth microstructures in the tapered SOA on the compression of ASE was investigated,and it was found that the saw-tooth microstructures of right-right angled triangle(device A)showed the best effect.The ratio of the maximum intensity to background radiation was increased by 21.9% and the power was increased by 30.5% compared with conventional SOA.Device A has an average power of 799 mW and a pulse width of 6.7 ps,corresponding to a peak power of 206 W.(3)Based on the theory that pulse compression can achieve femtosecond pulse duration,a two-pass transmission grating compressor is used to compress the picosecond light pulse output by the MOPA system.The pulse duration of 495 fs and a peak power of 1.5 kW were realized.