Study On Erbium-doped Fiber Laser With Bidirectionally Mode-locked By Carbon Nanotube

Mode-locked fiber lasers have potential applications in medicine,military,nonlinear optics,and high-speed optical communications.With the development of science and technology,mode-locked fiber lasers will also have many new developments.In this paper,we focus on the bidirectional passively mode-locked erbium-doped fiber lasers.Firstly,the research background of mode-locked fiber lasers is briefly introduced.Also,the development prospect and its significance of mode-locked fiber lasers are briefly analyzed.The principle of the mode-locking in the laser is presented.The different mode-locking types in mode-locked lasers and the different nonlinear effects in the cavity are both introduced.Then,the unidirectional passively erbium-doped fiber laser,which passively mode-locked by carbon-nanotubes,is demonstrated.It is found that the central wavelength changes around 1560 nm with the clear Kelly sidebands.Pulse width varying from 400 ps to 900 ps,repetition rate about 7.57 MHz,have also been obtained.Next,the bidirectional erbium-doped fiber laser,which passively mode-locked by carbon-nanotubes,is demonstrated with stable output pulse trains simultaneously from both directions of the laser cavity.By adjusting the pump power and polarization controller,the output characteristics under different pump powers are investigated.The spectrum of pulses changes with the different lengths of erbium-doped fiber.Especially,the pulse splits of the counterclockwise pulse trains have been observed.Finally,the numerical simulation,with the split-step Fourier method using MATLAB,is adopted to show the propagation of optical pulses in an erbium-doped fiber laser mode-locked by carbon nanotubes.By changing the parameters of the laser cavity,different types of pulses have been obtained.The output pulse characteristics are briefly shown with the influence of the different parameters in the laser ring cavity.