Research On Mode-Locked Fiber Lasers Based On Nonlinear Loop Mirror

Passively mode-locked fiber lasers are widely used in biomedicine,material manufacturing,high-speed optical communications and other fields due to their merits of high output power,compact structure,and good stability.Mode-locked fiber lasers based on nonlinear loop mirrors have attracted the attention of researchers due to their flexible structure,low construction cost and easy realization of all-fiber configuration.Nonlinear loop mirrors include nonlinear optical loop mirrors(NOLM)and nonlinear amplifying loop mirrors(NALM).Fiber lasers based on nonlinear loop mirrors are often used to generate high-energy dissipative soliton resonance(DSR)pulses.The pulse energy can reach more than four orders of magnitude of conventional soliton,which has extremely high practical application value.In this thesis,theoretical and experimental researches on mode-locked fiber lasers based on nonlinear loop mirrors are carried out.The main research contents are summarized as follows:1.A NALM-based figure-of-8 erbium-doped fiber laser is designed and constrcted.The total cavity length is 43.8 m and the net dispersion is-1.0 ps~2.It is a fully anomalous-dispersion cavity and realizes the conventional-soliton pulse output with switchable L-band wavelengths.The switchable wavelengths are 1577.7 nm,1595.0 nm and 1607.9nm.The pulse repetition frequency is 4.63 MHz,and the pulse width is 1.13 ps,1.18 ps and 1.08 ps.The total cavity length reaches 443.8 m by increasing the length of the single-mode fiber in the NALM,and the net intracavity dispersion is-10.2 ps~2.DSR pulse output with switchable L-band wavelengths are obtained.The pulse repetition frequency is 455k Hz.The maximum pulse width and single pulse energy of the obtained DSR pulses are233.5 ns and 61.1 n J,respectively.The vector characteristics of the DSR pulses are also studied,which confirms that the obtained pulses are polarization-locked DSR pulses.2.By replacing the single-mode fiber in the NALM with the dispersion compensation fiber,The total cavity length is adjusted to 313 m.The net dispersion of the cavity is 1.23 ps~2.DSR pulses with switchable wavelengths are obtained.The switchable wavelengths are 1572.9 nm and 1603.3 nm.The pulse repetition frequency is 648 k Hz.The maximum pulse width and single-pulse energy are 142.8 ns and 45.8 n J,respectively.3.Dissipative soliton(DS)and DSR pulses are numerically investigated in a figure-of-8 fiber laser based on NOLM.The NOLM is modeled by its transmission function.The generation conditions of the DSR pulses and the conversion process from the DS pulses to the DSR pulses are explored.By using the discrete device model,the generation of DSR pulses in the NALM-based figure-of-8 fiber laser is numerically investigated.The effects of cavity parameters including the intracavity filter bandwidth,coupling ratio of the coupler,the length and the nonlinear coefficient of the single-mode fiber on the DSR-pulse features are analyzed.4.Numerical simulation of figure-of-9 fiber lasers using fiber mirrors is presented.DS and DSR pulses are obtained,and the influence of the phase shifter on the pulse characteristics is analyzed.The figure-of-9 fiber lasers with a fiber bragg grating and a dumbbell structure are numerically simulated,and factors that affect the features of DSR pulses are analyzed.