Research On Active Time-domain Control Technology Based On Random Feedback Fiber Laser

Fiber random laser has been widely concerned by many scholars since its inception,and has a long-term application and development in the fields of national defense,industry and medical treatment.As an extension of the traditional random laser in the optical fiber system,the fiber random laser provides randomly distributed optical feedback by Rayleigh scattering in one-dimensional disordered scattering medium or fiber Bragg grating,and provides nonlinear gain by stimulated Raman scattering,stimulated Brillouin scattering or active fiber,which can produce random lasing in the cavity free structure.Erbium-doped fiber laser based on random distributed feedback grating array is a typical coherent fiber laser.When this kind of laser works,many modes are excited,and the mode competition is fierce,resulting in output wavelength jump and time-domain instability.Based on this,this thesis realizes the output mode locking of this kind of laser by using the active mode-locking technology,and realizes the quasi continuous and adjustable pulse output in the ring cavity with fixed cavity length.An active modelocked pulse with a lasing threshold of 84 m W was obtained experimentally;By combining the nonlinear polarization rotation effect and active mode locking technology,10 fundamental frequency active mode locking pulses in the frequency range of6.827～6.872 MHz are obtained with a fixed cavity length;In addition,8 second harmonic active mode-locked pulses in the frequency range of 13.654～13.724 MHz are also realized.This work provides an effective way to achieve stable mode output in disordered media,and also provides a useful platform for the study of photon localization in random structures.The fiber random laser based on Rayleigh scattering is a typical incoherent fiber laser.This kind of laser shows the characteristics of random fluctuation in the time domain under the ultrafast time scale of picosecond,which has great advantages in producing supercontinuum spectrum.Firstly,based on the semi-open cavity structure,the supercontinuum spectrum with 20 d B bandwidth of 212 nm is realized in the longdistance optical fiber system composed of true wave fiber and dispersion shifted fiber.With the increase of pump power,the spectrum continues to widen and Raman soliton fission phenomenon exists under the action of nonlinear effect.It is shown as a strong pulse with disordered distribution in the time domain,called optical strange wave.In this thesis,the transformation of optical strange waves from disordered distribution to quasi disordered distribution is realized by using active control technology,which provides a reference for the study of the distribution and control of random strong pulses in the generation of supercontinuum in optical fibers.