Research On Narrow Linewidth Brillouin Rare Earth Doped Fiber Laser And Active Mode-locking Technology

Interferometric fiber optic hydrophone systems have extremely high requirements for the linewidth of the light source（k Hz level）.The application of narrow linewidth fiber lasers is conducive to the improvement of its detection sensitivity and detection accuracy.For fiber-optic hydrophone arrays based on time division multiplexing technology,the repetition frequency and pulse width of the pulsed light source directly restrict the number of primitives,dynamic range,and signal demodulation difficulty of the system.Therefore,the research of fine linewidth lasers and pulsed lasers with tunable pulse width is of great significance for improving the performance of hydrophones.At present,most common narrow linewidth fiber lasers need to use complex linewidth compression methods,which are easy to introduce additional noise.Brillouin rare-earth-doped fiber lasers can convert MHz-level seed light sources into k Hz-level Brillouin lasers only through the stimulated Brillouin effect,which has broad application prospects.This paper takes Brillouin rare-earth-doped fiber lasers as the research object to study new narrow linewidth lasers and pulsed lasers that can meet the application requirements of interferometric fiber hydrophones and their array systems.In the research of narrow linewidth lasers,the Brillouin Er/Yb-codoped fiber laser（Brillouin Er/Yb-codoped fiber Fiber Laser,BEYFL）has the advantages of narrow linewidth（2k Hz）,low phase noise(-107d B/Hz^1/2@1k Hz),high output power（>100m W）and ultra-short gain fiber（<1m）.In the research of pulsed lasers,by adding an electro-optic phase modulator in the Brillouin Erbium-doped Fiber Laser（BEFL）cavity,the pulse width is continuously adjustable in the range of 5ns to 30.6ns.The main innovations of this paper are as follows:1.Using tens of centimeters EYDF as both linear gain medium and Brillouin gain medium,the BEYFL with narrow linewidth and low phase noise is realized.Compared with the BEFL based on several meters EDF,the BEYFL has more compact structure and higher output power,and is more suitable for remote hydrophone systems.2.By adjusting the BP power to change the shape of the gain spectrum,an active mode-locked Brillouin erbium-doped fiber laser（AHML-BEFL）with independently adjustable pulse width is realized,and has important application value in the field of sensing.