Stability and compression of pulses in the soliton laser

A theory of the soliton laser is presented which examines how an external optical fiber enables a laser to produce shorter pulses than it could produce alone. A phenomenological laser model, which shows how the lower limit to the mode-locked pulse width can arise, is first discussed. This model is coupled to an external optical fiber cavity, into which a part of the output beam is launched. The returning pulse from the fiber cavity is then mixed with a circulating pulse in the laser at the output mirror. Stable solutions are found which are nearly periodic in the external cavity. More than one solution for a given set of model parameters are also found, depending on the initial conditions. The radiation (nonsoliton) part of the propagation in the optical fiber cannot be ignored. It acts as a buffer between the tendency of the fiber to produce solitons, and the fact that a pure soliton is not an exact fixed point of the laser model.