Research On Fiber Random Lasers Based On Rayleigh Scattering Distributed Feedback

Different from conventional laser,random laser utilize multiple scattering of photons in an amplifying disordered medium to generate coherent light without a traditional resonator.It attracts the extensive attention due to its unique physical properties and potential applications.Since Turitsyn et al first proposed random distributed feedback fiber laser in 2010,research on fiber random laser has developed into a mature experimental and theoretical field.Compared with the disordered material random laser,it has advantages such as high directivity,high lasing efficiency,low threshold,long distance radiation,simple structure,etc.In consequence,fiber random laser has great potential applications in optical fiber communications and optical fiber sensing.So far,most fiber random lasers are realized by pumping km order single mode fiber with high power laser.Distributed feedback is provided by Rayleigh back-scattered light that amplified through Raman Effect over total fiber distance.Raman fiber random laser has higher threshold of watt order,on account of the low Rayleigh scattering coefficient.Based on Brillouin scattering and Er-doped fiber,threshold can be reduced to milliwatt order because their gain coefficients are much lager than Raman's.In addition,studies on fiber random laser mainly focus on continuous-wave,since i)lots of randomly distributed modes are coupled together,which generate emissions in all directions at various positions,depleting the accumulated energy in the cavity rapidly and making Q-switching difficult;ii)spectrum is the superposition of resonant mode with random frequency,presenting continuous distribution.Frequency-locking of mode-locking can't be satisfied due to their unequal frequency space.Hence,pulse fiber random laser are rarely reported,and studis on theory and experiment are still at the exploration stage.This research project mainly includes studies on continuous-wave,Q-switched pulse and self-phase locking pulse exported by fiber random laser:1)Output characteristics of open cavity Raman fiber random laser are investigated experimently.We use half-open cavity with fiber loop mirror and ring cavity to reduce the threshold,obtaining 1665 nm continuous-wave lasing,with thresholds of 0.9 W and 0.4 W,respectively.Meanwhile,the impacts of reflectivity and fiber length on output characteristics of half-open cavity are discussed.2)Exploiting Q-switching effect based on Rayleigh scattering-Stimulated Brillouin scattering(RS-SBS),the Er-doped fiber random laser is investigated experimently.Pulses accompanied by multi-wavelength are generated with threshold as low as 27 m W.The repetition rate is typically on the kilohertz scale with RMS timing jitter of < 5.5% and RMS amplitude fluctuation of < 30%.3)Exploiting self-phase locking based on cascaded Brillouin,the Brillouin fiber random laser is investigated experimently.Pulses are generated with repetition rate of 11 GHz and pulse width of ps order.We experimentally analyze the impacts of Brillouin pump and LD pump on the number of channels and spectrum power distribution.Besides,dc background in the pulse autocorrelator trace is also investigated.