Time Domain Characteristics Of Short Pulse Random Lasers Based On Disordered Polymer Optical Fibers

Different from traditional lasers,random lasers(RLs)have no resonant cavity,and the RLs are generated under the effect of optical amplification and multiple scattering of the disordered gain medium.Good output directivity and high power of the RLs can be achieved based on the waveguide confinement effect of 1D structure,which overcomes the uncertainty of emission direction and power instability in the traditional RLs.It is a challenging problem to realize the stable short pulse emission in the fiber RLs which can be solved by the time domain characteristics of fiber RLs.In this thesis,the time domain characteristics of RLs in disordered polymer fiber were studied for the first time.The coherent fiber RLs with narrow line width,low threshold and fixed emission frequency are realized,and the pulse width of short pulse RLs is adjusted.The results of this thesis are suitable to understand and investigate the dynamic process of RLs in disordered polymer optical fibers.The specific research contents and results are as follows:(1)Time domain characteristics of RLs in polymer fiber.Three kinds of disordered polymer fibers were prepared by the Teflon method,the spectral threshold and laser mode transition of RLs in polymer fiber were studied,and the coherent fiber RLs emission was realized.Moreover,the time domain distribution of RLs was discussed,and the internal mechanism and stability of the time domain were explained.The RLs pulse width is narrowed to the picosecond range when the pump energy increases,and the RLs pulse width stabilizes in the range of picosecond after long-term pumping,as a result,the periodic short pulse RLs emission with tunable pulse width was realized.(2)Time domain polarization characteristics of RLs in polymer fiber.By studying the time domain characteristics of the polarized RLs based on doped polymer fiber in its core,it is found that the fiber RLs are short pulse polarized RLs,and the formation mechanism was explained.The mean free path of scattering is changed by control of the refractive index of the polymer fiber when the applied temperature is adjusted,thereby the pulse width of the RLs can be modulated.(3)Time domain characteristics of RLs coated with polymer fibers.36 kinds of disordered polymer optical fibers coated with PM597 and POSS nanoparticles(NPs)were prepared by spin coating.By adjusting the degree of disorder to change the mean free path of scattering,it is found that the RLs peak wavelength of the polymer fiber blue shifts with increasing the degree of disorder,and the time domain pulse width became narrow.By adjusting the dye concentration to change the gain length,it is found that increasing the dye concentration,peak wavelength of the polymer fiber RLs red shifts,the time domain pulse width is continuously narrowed at low dye concentration,and slightly broadened at high dye concentration.Finally,it is found that the cladding-coated polymer fiber has good time domain stability and self-healing performance.