The All-fiber Passive Mode-locked Laser Using SESAM

The passively mode-locked fiber laser based on semiconductor saturable absorber mirror (SESAM) has recently attracted much research interests due to its wide application area and various advantages such as simplicity, compactness, high stability, low pump threshold, and all-fiber configuration etc. Continuous wave mode-locking (CWML) pulses can be successfully extracted from such lasers. Nowadays it has become one of focuses in ultra-short optics.In this thesis, SESAM mode-locked fiber laser in an all-fiber configuration is demonstrated. CWML based on SESAM and all-fiber cavity configurations is realized for the first time at home. A comparison between the lasers under the conditions of narrow- and wide-band limited mode is performed. Detailed observation and anatomization on the pulses' formation and evolvement process under different pump energy are provided in order to have an insight on the physical connotation of passively mode-locked fiber laser. And its intrinsic evolutive rules are concluded to lay a foundation for the improvement of laser. The main contents are outlined as follows:1. Theoretical partNumerical simulation on fiber lasers with SESAM passive mode-locking is carried out by using the nonlinear Schr(o|¨)dinger equation (NLSE). The evolvement processes of the mode-locked pulse shape with different gain and dispersion are presented in the simulation. The simulation results are qualitatively consonant with the experimental results.2. Experimental part(1) Q-switching, CWML and multi-pulse modulation effects are observed in an SESAM mode-locked fiber Bragg grating laser. Two SESAMs with different saturation fluence are utilized separately in the experiment. A stable mode-locked output with central wavelength of 1064.2 nm, a spectrum bandwidth of 0.5 nm, a repeat frequency of 17.3～27.0 MHz, and a pulse width about 40ps is obtained with the SESAM that exhibits a much lower saturation fluence. A multi-pulse modulation with pulse width of 15.1 ps is observed with the SESAM of high saturation fluence. (2) Steady Q-switching, Q-switched mode-locking, tunable CWML and multi-pulse modulation are realized separately in an SESAM mode-locked fiber laser that utilizes a home-made fiber loop mirror as one of the laser cavity. A steady CWML with spectral bandwidth about 10nm and pulse width of 17.4 ps is realized in this laser configuration. (3) Mode-locking effects in other kinds of cavity configurations, including a cavity with 4% fiber end output port and an amplifying-loop cavity, are investigated.The operating characteristics of SESAM mode-locked fiber laser are concluded through comparison analysis on the experimental results of the various laser cavity configurations. Also, the damage causation of SESAM is analyzed and some useful conclusion has been made. According to the experimental results and the analyses, a novel kind of passively mode-locked cavity configuration with two SESAM is proposed. The research results provide useful guidelines to those people who are involved in the same research topic and who want to utilize SESAM passively mode-locked fiber laser as a research tool.