Research Of Passively Q-Switched Fiber Lasers Based On 2D Material

Q-switching is one of the most important techniques to obtain laser pulses with short pulse duration and high pulse energy. Compared with conventional solid state lasers, passively Q-switched fiber laser is attractive to many people due to its compactness, low cost, and efficiency, and has been widely applied to fields such as laser processing, medicine, fiber communication and fundamental research. In recent years, two-dimensional materials such as graphene, transition metal sulfides(include MoS2 and WS2) and their van deer valls heterostructure have been researched around the world due to its unique optical and electronic properties. Therefore, it is of great scientific and practical importance to study on passively Q-switched fiber lasers based on two-dimensional materials.In this thesis, we mainly carried on experimental study on passively Q-switched fiber lasers based on two-dimensional materials, specifically on graphene, graphene/MoS2 heterostructure and graphene/WS2 heterostructure.Firstly, a wavelength widely tunable passively Q-switched fiber laser based on graphene was demonstrated and stable Q-switched operation was obtained. Monolayer graphene was fabricated by CVD grown method and then transferred to the end face of the fiber connector to form a graphene-based saturable absorber. By adjusting the tunable filter at the pump power of 80 mW, a tunable operation was obtained with a wide range of 70 nm(1519 nm to 1589 nm). The tunable characteristics as a function of the wavelength was analysed. At the wavelength of 1559.9 nm, the repetition rate varied from 8.55 to 38.26 kHz by adjusting the pump power and the minimum pulse duration was 3.45 μs with a max single pulse energy of 138.76 nJ.Secondly, a passively Q-switched Er-doped fiber laser with a linear cavity based on graphene/MoS2 heterostructure was demonstrated. The monolayer graphene and few-layer MoS2 was grown by CVD method. Then the graphene was transferred to a surface of MoS2 to form a graphene/MoS2 heterostructure by van der waals force. The saturable absorbtion characteristics of the graphene/MoS2 heterostructure was measured at the wavelength of 1550 nm. Stable Q-switching operation was obtained at the wavelength of 1559.97 nm. The repetition rate ranged from 15.53 k Hz to 45.03 kHz as a function of pump power and the minimum pulse duration was 1.36 μs with a max single pulse energy of 37.7 nJ. The characteristics was also discussed to improve the property of the laser.Thirdly, a widely tunable passively Q-switched Er-doped fiber laser with a ring cavity based on graphene/WS2 heterostructure was demonstrated. The two-dimensional graphene and WS2 was grown by a CVD method and then the monolayer graphene was transferred to the surface of WS2 to make up a graphene/WS2 van der waals heterostructure. The saturable absorbtion characteristics of the graphene/WS2 heterostructure was measured at the wavelength of 1550 nm. By adjusting the tunable filter at the pump power of 100 mW, a wavelength tunable operation was obtained with a wide range of 80 nm, from 1509 nm to 1589 nm. The tunable characteristics as a function of the wavelength was analysed. At the wavelength of 1550 nm, the repetition rate varied from 10.81 to 33.65 kHz by adjusting the pump power and the minimum pulse duration was 2.33 μs with a maximum single pulse energy of 147.2 nJ.