Short-pulsed Er-doped Fiber Lasers And Synchronously Pumped Mid-IR Optical Parametric Oscillators

The 1.5 μm short pulsed Er-doped fiber lasers have lots of attractive properties including compact design, robustness and superior beam quality. They can be widely used in many fields such as biomedical, optical communication, remote-sensing and material processing. The main methods to obtain short pulsed lasers are Q-switching and mode-locking. In this thesis, we demonstrated passively Q-switched and mode-locked Er-doped fiber lasers with graphene oxide as a saturable absorber, leading to generation of nanosecond, picosecond, and femtosecond short pulse at 1.5 μm respectively. The femtosecond pulses with high peak power can be used in nonlinear frequency conversion. Using femtosecond synchronously pumping technique, we built PPLN and Ga As based optical parametric oscillator(OPO) respectively, and obtained mid-IR lasers in 3-7 μm. This wavelength range is within the important atmospheric communication window and covers lots of molecule absorption line. Therefore, mid-IR lasers have many important applications such as spectroscopy, remote-sensing and military defense.The main research work in thesis includes the following parts:1. Graphene oxide based nanosecond Er-doped fiber lasersWe demonstated two methods for nanosecond pulse generation: passively Q-switching and noise-like mode-locking. Graphene oxide has lots of great properties, such as low price, easy fabrication, ultrafast recovery time, broadband operation wavelength and strong saturable absorption. Because of the present of oxygen-containing functional groups, graphene oxide has strong hydrophilic, which offers superior flexibility to form versatile optical components. First, we demonstrated graphene oxide based Q-switched Er-doped fiber lasers with ring cavity configuration. By increasing the pump power, the laser repetition rate increased from 68 k Hz to 124 k Hz, while the pulse width decreased from 1.6 μs to 470 ns. This type of Q-switched nanosecond Er-doped fiber laser has many potential applications due to the unique advantages including low price, compact design and excellent stability. Moreover, we reported graphene based noise-like nanosecond Er-doped fiber laser, which adopted ultra-long ring cavity. The cavity length is 515 m. The graphene absorber mirror used in this experiment was made by depositing the graphene-PVA composite on a gold mirror. The graphene was prepared by the low-temperature exfoliation under vacuum. The oscillator output laser pulses with 388 k Hz repetition rate and 6 ns pulse width. After the two-stage Er-doped fiber amplifier, we finally obtained 553 m W output power, corresponding to 1.4 μJ single pulse energy.2. Graphene oxide based mode-locked ultrafast Er-doped fiber lasersWe demonstrated mode-locked Er-doped fiber lasers based on novel material—graphene oxide. By managing dispersion, we obtained 200 fs pulses from the graphene oxide mode-locked Er-doped fiber laser. Then we added a segment of dispersion compensate fiber(DCF) into this cavity. We obtained dissipative soliton with high linear chirp, where the mode-locking operated in large normal dispersion regime. Based on the theoretical model, we analyzed the dissipative soliton evolution process and the possibility of pulse compression outside the cavity. Our numerical simulations are in good agreement with the experimental results. Besides, we demonstrated the all-polarization-maintaining(all-PM) graphene oxide mode-locked fiber laser. The output pulses have a repetition rate of 48.2 MHz and pulse width of 502 fs. The unique combination of the all-PM configuration and the novel graphene oxide saturable absorber offers an ideal approach to fabricate a compact single-polarization femtosecond source with high environmental stability.3. Femtosecond synchronously pumped mid-IR degenerate OPOWe demonstrated PPLN and Ga As based femtosecond synchronously pumped degenerate double-resonate OPO respectively. This kind of OPO generates broadband mid-IR laser pulses with pulse width below 100 fs and can be found useful in many applications in spectroscopy and biomedical research. The pump source of the PPLN based OPO was a femtosecond mode-locked Er-doped fiber laser. OPO adopted bow-tie cavity configuration. The feedback loop included detector, piezo and PID controller, which can adjust the cavity length to compensate the environmental disturbance, such as the air flow and mechanic vibration. The maximum output power is 70 m W with a slope efficiency of 31.45%. The optical spectral range is 2.5-3.8 μm. The pump source of the Ga As based OPO was a femtosecond mode-locked Tm-doped fiber laser. The threshold of this OPO is only 7 m W. The maximum output power is 73 m W with a slope efficiency of 40%. The bandwidth is from 2.6 μm to 7.5 μm. We performed dual-comb spectroscopy using a pair of broadaband(3.2-5.3 μm) Ga As OPO frequency comb sources with the resolution of 0.07 cm-1.The main work is done in two institutes. The nanosecond Er-doped fiber laser and ultrafast mode-locked fiber laser were done in Beijing University of Technology, and the mid-IR OPO was done in University of Central Florida, US.