Design And Implementation Of Intelligent Polarization Control System For Automatic Mode-locked Fiber Laser

Mode-locked fiber lasers have the advantages of short pulse width,high pulse peak power,wide spectrum and high signal-to-noise ratio.They are widely used in optical frequency measurements,high-resolution atomic clocks,signal processing,ranging metrology and astronomy.It has become one of the research hotspots in the field of optoelectronic technology.Among them,nonlinear polarization rotation-based passively mode-locked fiber lasers have been widely studied due to their simple structure,superior performance and rich nonlinear dynamics in the cavity.However,their sensitivity to polarization limits their widespread application.To address this,automatic mode-locking immune to environmental disturbances come into being.The long mode-locking time and long recovery time from disturbance of the existing automatic mode-locking schemes limit the practical applications in engineering.Aiming at this problem,the first intelligent programmable mode-locked fiber laser based on our proposed human-like algorithm is presented in this thesis.It can use the computing capability and precision of the machine to simulate the human mind and perform real-time polarization adjustment to achieve mode locking.This scheme uses a highspeed analog-to-digital conversion chip and field programmable gate array to collect,store and trigger high-speed real-time data,performs data processing in ARM processors and performs feedback control of electrical polarization controller in the laser cavity through high-speed digital-toanalog conversion chips to realize high-speed real-time polarization state adjustment.The laser is capable of automatically locking onto multiple operation regimes,such as fundamental mode-locking,harmonic modelocking,Q-switching and Q-switched mode-locking without physically altering its structure.And it can recover quickly after losing mode-locking mode due to environmental disturbances.For the fundamental mode-locking,the shortest initial mode-locking time and recovery time from detachment are only 0.22 s and 14.8ms,respectively,which are the new record in the field of automatic mode-locking.We believe that this intelligent modelocked fiber laser with multi-regime recognition,fast mode-locking,low cost and high stability will have extensive applications in scientific research and engineering.In addition,in other researches related to polarization control,the response speed of polarization control is a major factor limiting the performance.In order to improve the response speed of polarization control,a novel optical structure based on low-speed electronic polarization controller and high-speed phase modulator is proposed in this thesis to realize ultrafast polarization control.The response speed of the proposed polarization control reaches 50 ps which is about 200 times faster than the fastest commercial electronic polarization controller at present,providing powerful support for polarization-related technical research.