Abstract

I derive a nonlinear differential equation for the pulse envelope propagating into a soliton laser in which the output coupling and the coupling of the external nonlinear cavity are distributed along the gain medium of the main cavity. For a mismatch phase angle of π/2 between the two cavities, a stable opical soliton is the solution to the differential equation for negative dispersion (soliton into the fiber), as well as for positive dispersion, of the nonlinear external medium. The predicted width of the soliton pulse is a function of the coupling factor and of the intensity into the optical fiber. I also show that the operation of the soliton laser for this stable regime is similar to passive mode locking by a fast saturable absorber. Dark soliton is another possible regime. However, the gain required io sustain it is always higher than that required for the bright-soliton regime. For a critical value of the gain relative to the dispersion, another short-pulse regime is predicted that is in competition with the soliton regime. Bistable operation of the soliton laser is, therefore, possible at this point.

© 1990 Optical Society of America