Research On Multiple Wavelength Narrow Linewidth And Self Pulsing Mechanisms And Properties Of Brillouin Erbium Fiber Lasers

The Brillouin fiber lasers are a kind of light source with multiple lasing wavelengths,and it can be used in many fields,such as optical communication and optical sensing.Many properties of the Brillouin fiber lasers,such as threshold,Stokes wavelength quantity,the line-width for a specific Stokes wavelength,the frequency spacing between two adjacent wavelengths and the time doming self-pulsing property have been widely investigated.Based on these mentioned investigations,we research on the following properties of the multi-wavelength Brillouin Erbium fiber lasers: the frequency spacing switchable property,the line-width narrowing mechanism introduced by Rayleigh back scattering and the self-pulsing property of high order Stokes lasing light.For the property of switchable frequency spacing,a new hybrid Brillouin Erbium fiber laser scheme that employing cascaded multiple Brillouin gain fibers in a ring cavity to realize multi-wavelength laser output with switchable frequency spacing is proposed and experimentally investigated.The multiple frequency down-shifting processes introduced by multiple stimulated Brillouin scattering(SBS)effects in one round trip of the cavity make it possible to realize multi-wavelength output with frequency spacing which is an integer multiple of SBS frequency shifting.With two cascaded SBS fibers,the frequency spacing can be switched between single and double SBS frequency shifting by properly adjusting Brillouin pump power.Multi-wavelength outputs with triple or quadruple SBS frequency spacing are also demonstrated by employing three or four SBS gain fibers,respectively.For the property of multiple wavlength and narrow linewidth,a novel Rayleigh backscattering assisted Brillouin Erbium fiber laser scheme with multi-wavelength narrow line-width output is proposed and investigated experimentally.The stimulated Brillouin scattering and Rayleigh backscattering take place at two conventional single mode fibers(SMFs)respectively.The Rayleigh backscattering is used as a mechanism to compress the line-width of each Stokes component,and it has been realized and maximized in conventional SMF by optimizing injection power of Stokes light through adjusting the variable optical attenuator(VOA)in front of the fiber.By adjusting VOA attenuation,the laser can obtain 3 wavelengths output with 3 dB line-width less than 2 KHz for each wavelength,or 6 wavelengths output with 3 d B line-width less than 5 KHz.For the property in time domain,the fundamental and harmonic self-pulse generation is experimentally observed on both first order and higher order Stokes components.The generated pulses with the same order harmonic repetition rate are obtained on multiple Stokes components simultaneously.The harmonic pulse generations up to fifth order have been achieved.The above mentioned investigations have improved the many kinds of properties for the Brillouin Erbium fiber lasers,and it can potentially provide light source for many kinds of applications.