Research Of Ring Erbium-doped Fiber Mode-locked Laser Based On Graphene Saturable Absorber

With the progress of science and technology, ultra-short pulse is playing an increasingly important role in industrial production and science research with its standout qualities. It can be widely applied in many areas such as optical communication, micro-processing, bio-sensing and terahertz waves. Fiber laser have advantages of good gain characteristics, small size, low threshold power, high conversion efficiency, high output beam quality and compatibility with existing communication system. So it has become a research focus in the ultra-short pulse technology.The ideal method to obtain ultrafast pulse is though a semiconductor saturable absorber mirror as fiber laser mode-locker. But because of its narrow absorb bandwidth the semiconductor can only be used in the near-infrared bands, and its preparation method are complicated and costly. These limit the development of ultrafast laser. Carbon nanotubes as a direct band gap material are also used in the optical fiber laser as a stability mode-lock. But it will produce a great scattering loss due to the form of the carbon nanotubes, which improve the locking threshold and limit the laser output power and efficiency. In recent years, graphene was discovered to have a very unique saturated nonlinear optical absorption characteristic and start mode-locking to generate pulsed laser. The production method of graphene is relatively simple. As a saturable absorber material, graphene has a large absorption bandwidth, non-saturated loss and high damage threshold, has a wide application prospects. Exploring graphene"s nonlinear saturable absorption properties has become a hot topic in the field of the mode-locked laser. This paper is a research based on graphene as a saturable absorber erbium-doped fiber laser, specific work including:Introduce the history of the development of the optical fiber amplifier and analysis erbium-doped fiber amplifier work principle. The effects of the pump power and the length of the erbium-doped fiber on the fluorescence spectrum were investigated in this paper. Experimental research in the erbium-doped fiber laser, the paper abtains the optimum length of the erbium doped fiber in the experiments is about10m. Further analysis fiber laser cavity especially linear cavity, and experimental study carried out on the basis of a continuous laser.Derive the fiber laser mode locking theory and analyse the mode-locked pulse mechanism. Introduce actively mode-locked and passively mode-locked technology from a mode-locked laser classification. Analyse the principle of saturable absorber in passive mode-locking. Analyse the transmission of pulse in fiber.Introduce and analyse this new material of graphene, its saturable absorption characteristics and mechanism. With depth modulation and high damage threshold, it is an ideal material as a saturable absorber mode-locking. Summarize the preparation and transfer process of the experiment obtained graphene. Its Raman spectra were measured before used in fiber laser. Experimental study the graphene as a saturable absorber in the structure of the annular fiber mode-locked laser. Analyse the experimental results to obtain graphene is a good material in the mode-locked laser.Finally, the paper has a summary and outlook to the follow-up.In short, the paper is driven by the requirements of ultrafast pulse, analyse erbium-doped fiber amplifiers and erbium-doped fiber laser, experimental study them as the same time. Analyse the mode-locking principle and use graphene as a saturable absorber in erbium-doped fiber laser.