Study On Pulsed Fiber Lasers With CNT?Graphene Saturable Absorber

Pulsed fiber laser has advantages of good beam quality. It is simple and compact, easy to integrate, cheap, etc. It is widely utilized in the optical fiber communication, ship-building industry, medical equipment, large-scale infrastructure, military security and defense, laser marking, laser cutting. Using saturable absorber for passive mode-locked laser, Q-switched laser can output nanosecond, picosecond or femtosecond ultrashort pulse. This is a simple and effective method. Carbon nanotube and graphene materials have advantages of large operating bandwidth, high damage threshold, fast recovery time and simple manufacturing method, which are prepared as saturable absorber to achieve mode-locked pulse, Q-switched pulse. This experiment uses carbon nanotube, graphene material in erbium-doped ring cavity to achiece mode-locked pulse and Q-switched pulse. We can not only observe the phenomenon of fundamental mode-locked pulses, harmonic mode-locked pulses, bunch of pulses, soliton rains, but also explain these theoretically. The main works are as follows:1. We firstly present the types and characteristics of Q-switched fiber lasers, mode-locked fiber lasers. We focus on presenting the research progresses of carbon nanotube, graphene, which are used as the saturable absorbers in fiber laser to ahieve Q-switched pulses and modelocked pulses.2. We introduce not only the basic principle of Q-switched pulses and mode-locked pulses, but also the saturable absorption principle of graphene. We briefly describe optical properties of carbon nanotube and graphene. Raman spectroscopy is used to detect carbon nanotube material and graphene material. Polyvinyl alcohol material is prepared to make graphene-PVA films, which are diffirent concentration. The preparation process is also described in detail.3. The erbium-doped fiber laser, which is based on carbon nanotube saturable absorber, is built. The nonlinear optical property of carbon nanotube saturable absorber is utilized to achieve mode-locked pulse. The pulse repetition frequency is 24.39 MHz, pulse width is picosecond. The spectrum wavelength of mode-locked pulse is 1559.37 nm, 3 dB spectral width is 9.29 nm, single pulse energy is 66 pJ. By adjusting polarization controller, diffirent types of multi-pulses can be output, including second harmonic mode-locked pulses, bunch of pulses, soliton rains.4. We partially cover the fiber core by CNT material. Based on the Mach-Zehnder interferometer principle, we can get mode-locked pulses in EDFL cavity. We clearly observe interference spectrum. The free spectral range value is 1.388 nm, single interference peak intensity can reach 10.4 dB. By adjusting PC, the bunch of pulses export. The interference disappears after CNT material completely cover fiber core.5. We use graphene-PVA films of different concentrations to achieve Q-switched pulses. When pump power is different, the average output power, pulse energy, pulse width varies.