Additive Pulse Mode-Locking and Fiber Lasers

Additive Pulse Mode-Locking (APM) is a particularly convenient means of generating pulses from fiber lasers, The figure eight self-stabilized laser by Duling is an example. Here the fiber ring(s) act as the pulse forming elements. It is desirable to construct simpler modelocking structures within one self-stabilized fiber resonator. Such structures are theoretically possible. They operate by nonlinear polarization rotation and use polarization transformers and polarizer(s), all compatible with, and realizable within, the gain fiber. They can be self-starting. Details of such designs will be given. One of these is being pursued experimentally at MIT. The aim is to adjust the parameters so as to produce a single soliton-like pulse bouncing back and forth in the resonator; the bandwidth limiting by the gain and loss profiles compensated by the APM action. It turns out that the APM action coupled with steady state gain saturation "quantizes" the solitons, giving them a characteristic energy. Therefore, in such fiber systems, one often encounters multiple solitons of equal energy bouncing back and forth as seen by the group at Strathclyde. We shall present the theoretical framework for the description of such systems.