Research On The Realization Of Novel Random Fiber Laser And Its Applications

As one of the most important laser sources,fiber lasers have varouis advantages such as the simplicity,excellent beam profile,high efficiency,convenient thermal management and the low power consumption.Fiber lasers have been used as indispensable tools in many fileds,such as the spectroscopy,biomedicine,industrial manufacturing,nonlinear optics and the national defense.Recently,a novel kind of fiber laser called random fiber laser has attracted lots of attentions among researchers.Different from a traditional fiber laser in that the feedback is provided by a resonant cavity formed by reflection components,random fiber laser has no specific resonant cavity.Therefore,random fiber lasers have some intrinsic advantages such as more simiplicity,higher realibility and more flexibility.Recent works have demonstrated the random fiber lasers have shown their dinstict advantanges in high power,high efficiency output,multiwavelength generation,wavelength tenability and several applications.However,as a newly developing topic,there is still a lot of space in the study of random fiber lasers,such as their output properties and underlying physical mechanism,their performance enhancement and structural optimization,and also the exploration of potential applications.Under the surport of of major project of National Nature Science Foundation of China(NSFC),our team has achieved lots of important results in the filed of random fiber laser.The results on the short cavity random fiber laser has been highlighted by the OSA in 2014 and open the door for the research on the high power random fiber laser.This thesis takes the Rayleigh scattering based random fiber laser as the research body and carries out a series of work on the realizations of novel random fiber lasers and their applications.Utilizing the concept of hybrid gain,several high performance random fiber laser at different wavelength regions have been demonstrated.Sevaral campact and cost-effective cascaded Raman random fiber lasers are proposed.The spectral statistic analysis of Raman random fiber laser is investigated.For applications,random fiber laser is used as the light source in temporal ghost imaging due to its excellent random temporal intensity fluctuatuions.Ulitilizing the simpilicty,high power ooutput and flexibility in output wavelength of random fiber laser,the random fiber laser can be an ideal source to act as the pump in high order Raman amplification stystems.The main contents and results of this thesis are summarized as follows:(1)Introducing the progess and the theoretical model of random fiber lasers.Proposing the weakly-doped ytterbium random fiber laser which can use the ytterbium fiber as both the gain and the random feedback medium.The numerical modelling results show that by optimizing the doping concentrate,low thereshold and high efficiency random lasing can be realized based on hundreds meters long ytterbium fiber.(2)Utilizing the characteristics of different gain types and the cavity design,several novel hybrid gain random fiber lasers are realized.A low threshold and high efficiency random fiber laser is achieved at 1.5 ?m by using the backward-pumping scheme and erbium-Raman hybrid gain.65.5% optical conversion efficiency is demonstrated experimentally at only 2 W of pump power,which is the reported highest optical conversion efficiency in this wavelength region.Designing the novel common cavity yetterbium/Raman random fiber laser,which can generate the ytterbium-doped random lasing and yetterbium-Raman random lasing successively.The common cavity design provide a simpler platform for 1 ?m high efficiency random lasing.Designing the halfopened ytterbium-Brillouin random fiber laser and realize the multiwavlength Brillouin random lasing at 1 ?m for the first time.(3)Designing and realizing several novel cascaded Raman random fiber lasers.The pump combiner in the ytterbium-doped fiber laser and the broadband reflector are used to form forward pumping scheme for generating cascaded random Raman lasing,thus avoiding the need of fiber Bragg gratings and Wavelength Division Multiplex with high power handling ability to construct the cavity for cascaded Raman random fiber lasers.Futher,designing the novel cascaded Raman random fiber lasers pumped by the ytterbium amplified spontaneous emission souce without fiber Bragg gratings or Wavelength Division Multiplex,which can have the better temporal stability.For multiwavelength cascaded Raman random fiber laser,a fiber loop mirror incorporating multimode interference filter is used as the point reflector.This multiwavelength cascaded Raman random fiber laser has adcantages such as easy fabrication,wide operating wavelength range,and low-cost.(4)Inspiring by the polarization-dependent properties of Raman random fiber laser,a polarization modulated random fiber laser is proposed for the first time by controlling the polarization state of Stokes light in the fiber loop mirror.Besides,statistical behavior of the output spectra in a Raman-gain random fiber laser is investigated for the first time.The experiment verifies that,for the random lasing based on the Raman gain and Rayeigh scattering,the statistical evolution as the injected pump power increases can also exhibit the transition from a Gaussian to a Lévy and then back to a Gaussian distribution.(5)Exploring several applications of random fiber lasers.The temporal intensity analysis of ytterbium-doped random fiber laser verifies that random lasing's temporal intensity shows excellent randomness,thus enabling its application on temporal ghost imaging.The results show that the temporal ghost imaging signal based on the random fiber laser has the better quality and accuracy comparing with that of the traditional fiber laser.As for the high order Raman amplification system,cascaded Raman random fiber laser can provide an effective solution for 1.2 ?m laser sources.Utilizing a 1280 nm Raman random fiber laser as the pump source in the third-order Raman amplification system,a 100 km long distance quasi-lossless fiber-optic transmission isexperimentally performed with 1 dB of signal power variation by using the 3rd-order Raman amplification,which is the longest quasi-lossless transmission system reported to date.