Research On Phase Noise Reduction Technologies Based On Brillouin/Erbium Fiber Lasers

In automatic control,on-line detection,fault diagnosis,medical examination and safety alarms fields,the high-coherence optical fiber sensing system is widely used because of its high sensitivity,high spatial resolution,fast dynamic response,strong anti-interference ability and good confidentiality.However,with the rapid development of highly integrated and micro sensor systems,the phase noise of laser is more and more prominent for the performance of the system,and the noise problem has aroused widespread concern.Brillouin erbium-doped fiber lasers?BEFL?have an ultra-narrow linewidth and ultra-low phase noise characteristics due to their narrow Brillouin gain spectrum,which makes it to be an important light source for coherent sensing.This thesis studied the basic characteristics of the compact ultra-short cavity BEFL,which used a short erbium doped fiber?EDF?to provide both Brillouin gain and linear gain.The structural parameters to obtain Stokes lasers from theory and experiments was studied,also the phase noise suppression characteristics and the impacts by the EDF length and the filter bandwidth were investigated in this paper.Besides,a cascaded BEFL was built to study the phase noise suppression by this laser.The main research work and innovation are as follows:?1?The basic working characteristics of the ultra-short cavity BEFL were studied by experimental methods and the relationship between the threshold power of the pump laser and the output power was obtained.This thesis studied the influence in mode competition of pump power,filter bandwidth and the center wavelength position of filter.In addition,the Brillouin pump wavelength range under different filter bandwidth to guaranteen BEFL mode output was investigated.?2?This thesis theoretically studied the phase noise suppression and the line-width compression capability of the ultra short cavity BEFL and verified the consistency of phase noise suppression and line width compression.It was found that the ultrashort cavity BEFL can convert the semiconductor laser who had poor phase noise characters to Brillouin Stokes laser whose phase noise was only-124 dB/Hz^1/2?at 1kHz,185m OPD?and the linewidth was extremly narrow.?3?The effects of pump power,EDF length and filter bandwidth on BEFL phase noise were studied.It was found that long EDF length was better for phase noise suppression effect,while the increase bandwidth of filter would impair it.?4?It was found that the phase noise suppression effect of the two-stage BEFL was equivalent to that of a single BEFL,that is,a single BEFL had been able to compress the lineiwidth and reduce the phase noise of Brillouin pump to its limit.