Experimental Research Of Pulsed Erbium-doped Fiber Laser Based On A 45 Degree Tilted Fiber Grating

Nowadays,people have entered the era of high-speed information interaction with the rapid development of science and technology.From the ancient beacon tower,flag language communication,telephone communication in 20^th century,and then to optical communication which employs the light as the carrier,communication equipment has been pushed into the strategic emerging industries to meet the needs of high-speed communication in China.Laser plays an important role in the optical communication system.Therefore,the nanosecond short pulse,the picosecond/femtosecond ultrashort pulse provide the reliable source of optical communication based on the passively Q-switched or mode locked technology.Two popular methods to generate pulses are saturable absorbers with nonlinear optical properties and nonlinear polarization rotation?NPR?technique.Due to easy operation of NPR technique and high polarization dependent loss?PDL?,low insertion loss,compact structure,nice compatibility with other in-fiber components of 45°tilted fiber grating?45°TFG?,we can achieve short,and ultrashort pulse output in 1.5¹.6?m band.In this dissertation,we pay major attentions on passively Q-switched and mode locked Erbium-doped fiber lasers based on 45°TFGs,including nanosecond,picosecond,femtosecond pulse generation and relationships between PDL of 45°TFG and output characteristics of fundamental soliton Erbium-doped fiber lasers.The main research results are as follows:1.We have studied the passively Q-switched Erbium-doped fiber laser based on the NPR technique.At first,we briefly describe the mechanism of passively Q-switched technique.Then,we design a passively Q-switched Erbium-doped fiber laser based on a 45°TFG.Owing to the NPR effect,stable Q-switched pulses with an average output power of 17.5 mW,a single pulse energy of 72.7 nJ,a repetition rate of 241 kHz,a pulse width of 466 ns are obtained under the pump power of 600 mW.The signal to noise ratio?SNR?of 58.8 dB is the highest among all-fiber passively Q-switched Erbium-doped fiber laser now.The stability of this Erbium-doped fiber laser is also examined by monitoring the laser consecutively for 5 hours at the laboratory conditions.2.We have designed a narrow bandwidth passively mode locked picosecond Erbium-doped fiber lasers based on a 45°TFG.In this fiber laser cavity,we employ a circulator to replace the polarization-independent optical isolator.Therefore,we can obtain the single direction operation in the laser cavity.A uniform FBG served as the intra-cavity filter is incorporated in the cavity through an optical circulator.To the best of our knowledge,0.15 nm spectral width is the narrowest among all-fiber passively mode locked Erbium-doped laser based on NPR effect now.3.We have studied the different value of PDL having influences on the characteristics of the output pulses.Firstly,we set up the fundamental soliton Erbium-doped fiber laser based on a 45°TFG.Then,the different output characteristics are recorded by replacing the 45°TFG with different PDLs while keeping the same laser cavity length.We can conclude the following points,with the increasing of PDL value,the threshold of fiber laser has a decreasing trend when the efficiency of the output laser keeps elevating.Thus,the time-bandwidth product?TBP?,SNR,energy fluctuation,and calculated time jitter basically remain unchanged.Therefore,we employ a 45°TFG with high PDL value as the in-fiber polarizer to construct an ultrafast Erbium-doped fiber laser.Furthermore,we have realized 65 fs ultrashort pulse generation by optimizing the intra-cavity dispersion and compressing the output pulse duration.