Investigation Of Passively Mode-Locked Fiber Lasers Based On Carbon Nanotubes

Passively mode-locked fiber lasers are widely used in fiber communication systems,laser processing,high-speed medical imaging,high-power laser systems and many other fields as they can generate output pulses with ultrashort pulse duration,high peak power and wide spectral width.Single-walled carbon nanotube(SWCNT)saturable absorber(SA)have many advantages such as fast recovery time,low saturation intensity and wide spectral range.SWCNT-based mode-locked fiber lasers are one of the hotspots in laser technology.Researches on high performance SWCNT-based passively mode-locked fiber lasers have important academic significance and application value.In this thesis,SWCNT-based bidirectional mode-locked fiber laser,dissipative soliton fiber laser and the vector characteristics of the output pulses are studied theoretically and experimentally,the main contents are as follows:The optical absorption of SWCNT is experimentally characterized.Then a bidirectional mode-locked fiber laser based on SWCNT is set up,which generates stable bidirectional output pulses centered at 1566 nm and 1566.7 nm with spectral width of 3.7 nm and 3.6 nm,the pulse duration of the bidirectional pulses are 0.75 ps and 0.77 ps,respectively.The effects of intracavity birefringence and cavity structure on the bidirectional pulses characteristics are analyzed.And we also numerically simulated the bidirectional mode-locked fiber laser.A SWCNT-based mode-locked fiber laser with net positive dispersion is set up,stable dissipative solitons output with central wavelength of 1561.7 nm,spectral width of 7.4 nm and pulse duration of 39.2 ps are obtained.And the variation of dissipative soliton pulses properties with pump power and polarization state are studied.The output pulses are compressed outside the cavity,the shortest duration of the compressed pulse is 0.76 ps,the compression ratio is 51.6.Vector solitons in SWCNT-based conventional mode-locked fiber laser and dissipative soliton fiber laser are studied,by adjusting the polarization controller to change the intracavity birefringence with different pump power,polarization locked vector soliton(PLVS),polarization rotation locked vector soliton(PRLVS)and group velocity locked vector soliton(GVLVS)are obtained.A ‘pulse tracing' method is adopted to simulate the SWCNT-based dissipative soliton fiber laser.The formation and evolution of the dissipative solitons are numerically simulated.By changing the intracavity birefringence beat length and small signal gain coefficient,PRLVS and GVLVS are numerically simulated.The effects of the intracavity birefringence on the vector solitons are also analyzed.