Additive Pulse Mode-Locked Erbium-Doped Fiber Lasers.

This thesis reports work in additive pulse modelocked (APM) erbium-doped fiber lasers. These devices have the potential to be compact, robust sources of ultrashort, broad-bandwidth pulses in the important 1.5 mu m wavelength region. Two different approaches to the design are discussed. They are referred to as soliton and non-soliton systems. Analytic theores are presented for each. These models are appropriate when the pulse experiences small net changes per pass due to linear and nonlinear effects in the laser. Computer simulations extend the modelling to the regime of larger nonlinear changes per pass. Experimental systems are found to be in reasonable agreement with theory. The working systems demonstrate that unidirectional ring cavities facilitate self-starting of the pulses from noise. The soliton and non-soliton regimes of operation are experimentally examined. Ultrashort pulses of high energy are demonstrated with the method of Stretched-Pulse APM, which uses segments of large positive and negative dispersion fibers to lower the peak intensity in the cavity. Sub-100 fs pulses with >0.5 nJ energy were generated directly from the cavity. The shortest pulses obtained were 63 fs, which is close to the gain-bandwidth of erbium. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).