Multi-wavelength Brillouin-raman Random Fiber Laser With Wide Bandwidth

Benefitting from inherent characteristics of good stability,broad bandwidth,tunability and simple structure,the multi-wavelength Brillouin-Raman random fiber laser(MBRRFL)can be applied not only in dense wavelength division multiplexing(DWDM)system to expand optical communication capacity,but also in optical filtering,optical fiber sensing and other fields,which has become a research hotspot in recent decades.This type of multi-wavelength random fiber laser uses the hybrid gain of stimulated Brillouin scattering(SBS)and stimulated Raman scattering(SRS)in the fiber to achieve a wide bandwidth and narrow linewidth multi-wavelength output,and the weak random Rayleigh(RS)scattering in the fiber provides optical feedback.Compared with other lasers with actual reflection devices,it has the advantage of a simpler structure.In this thesis,two frequency interval switchable MBRRFLs have been achieved by controlling the laser cavity loss or the power ratio of bidirectional Brillouin pump(BP),and the frequency spacing in them can be flexibly switched without changing the structure,which can improve their application flexibility.Further,by enhancing the synergistic nonlinear effects in fiber,the ultra-wide bandwidth multi-wavelength output is obtained.The main researches are as follows:1.A frequency interval switchable MBRRFL based on cavity loss regulation is designed.By controlling the attenuation value of reflective ring on the right side,the laser cavity can be switched between the full-open cavity and the semi-open cavity structure.In the experiment,the influence of different attenuation value of the reflective ring,BP and Raman pump(RP)parameters on the output spectrum are discussed.In the end,when the attenuation value of reflective ring is-2 d B,the fiber laser has a semi-open cavity structure,and thus a multi-wavelength output with a bandwidth of39 nm and a single Brillouin frequency shift interval is obtained;and when the attenuation value of reflective ring is-30 d B,the fiber laser has a full-open cavity structure,and thus a multi-wavelength output with a bandwidth of 39.5 nm and a double Brillouin frequency shift interval is obtained.2.A frequency interval switchable MBRRFL based on the power ratio of bidirectional BP regulation is designed.The laser has a full-open cavity structure and the forward and backward pump of BP in which is realized through an optical coupler.In the experiment,the output spectra of different pumping ratios are discussed after optimizing the conditions,and finally,a multi-wavelength output with a bandwidth of 42.5 nm and a single Brillouin frequency shift interval and a multi-wavelength output with a bandwidth of 44.5 nm and a double Brillouin frequency shift interval are obtained.3.An ultra-wide bandwidth MBRRFL is designed.It should be pointed out that the proposed laser has two outstanding characteristics: one is that the relatively long fiber combination and the other is strong bidirectional pumping.Due to the strong RP power and long gain optical fiber,the synergistic nonlinear effect in the cavity is enhanced,which promotes the Brillouin Stokes line(BSL)oscillation,which competes with the additional longitudinal mode oscillation,so that more energy is transferred to the BSL.In the experiment,a multi-wavelength output with an ultra-wide bandwidth of 63.5 nm and a double Brillouin frequency shift interval is obtained.This ultra-wide bandwidth MBRRFL is expected to be applied to DWDM systems which can greatly expand optical communication capacity and promote the development of all-optical networks.