| Random fiber laser(RFL),which is a new type of fiber laser,has received widespread attention and research since it was proposed.While compared with the commonly used method of using a high peak power pulsed fiber laser to pump a piece of photonic crystal fiber(PCF),supercontinuum(SC)generation by the RFL has the merits of simple structure,low cost and perfect robustness.Recent studies have shown that by using the RFL to generate SC is expected to obtain a broadband optical source with low intensity noise and low coherence,which can be applied in the fields of optical coherence tomography and nonlinear spectroscopy.This thesis studies SC generation directly from a RFL and the main research contents are summarized as follows:1、SC generated in an all-polarization-maintaining random fiber laser structure is studied.A linearly-polarized SC with an average output power of 4.43 W and spectrum covering from 600 nm to 1900 nm is obtained,and the polarization extinction ratio(PER)of the SC is greater than 18 d B at the highest output power.The spectral characteristics of SC generated from the linearly-polarized RFL and unpolarized RFL are compared.Owing to the high Raman gain of the polarization-maintaining germanium-doped fiber,the generated SC from the linearly-polarized RFL has better spectral width and flatness.To the best of our knowledge,this is the first demonstration of a linearly-polarized SC generated directly from a RFL.2、A near-infrared SC generated in an ultarshort cavity configuration is proposed,and the overall length of the SC is 11.5 m.While compared with the traditional SC generation method using the optical fibers with the length of tens of meters or even thousands of meters,the length of SC is shortened by more than 50 %.A near-infrared SC with an average output power of 26.8 W and spectrum covering from 900 nm to2000 nm is demonstrated,and the 976 nm laser diode pump to SC conversion efficiency is up to 60%.To the best of our knowledge,this is a near-infrared SC with the shortest fiber cavity length ever reported.3、SC generated in a RFL based on PCF is proposed.At present,the output of SC generated from the RFL has the issue of narrow spectral bandwidth and poor spectral flatness.To solve this issue,a piece of PCF is utilized in the half-opened RFL which is used to provide random distributed feedback as well as the nonlinear medium for spectral broadening.A flat SC which spread from 400 nm to 2300 nm with a 20 d B bandwidth of more than 1600 nm is obtained.To the best of our knowledge,both the spectral bandwidth and flatness are the state of the art for SC generation directly from a RFL.Simultaneously,SC generation in self-Q-switched fiber laser with PCF is also studied.A SC with an average output power of 50.7 W and spectrum covering from 500 nm to 2400 nm was realized.To the best of our knowledge,this is the highest power of SC generated in a single-stage self-Q-switched fiber laser ever reported.4、The space application of SC generated from a RFL is studied.In order to meet the requirements of SC to follow the aircraft into space,a prototype of SC which is applicable for space application is designed and built based on the scheme of SC generation from a RFL.The vibration test which are based on the space related test stands are carried out by the aerospace sector.Experimental results demonstated that the prototype of SC has good stability in terms of output power,spatral bandwidth and flatness,which suggested that the technical indicators are basically consistent before and after the test.This study laid a solid foundation for the subsequent in-orbit application of SC. |
