Theory of The Active Nonlinear Coupler Laser

Abstract

In a recent paper we proposed a mode locking scheme based on an active nonlinear directional coupler.1 This scheme relies on the saturable absorber-like action of a nonlinear coupler along with the soliton shaping and amplification effects that occur in an erbium doped fiber laser. Pulses shorter than 100 fs were shown to be feasible in a simple dual-core fiber geometry. Since erbium fiber lasers operate in the negative group velocity dispersion regime, the formation of soliton-like pulses in this system is not unexpected. For fiber lasers with positive group velocity dispersion, the creation of solitary pulses without the benefit of dispersion compensation is not obvious. This work, then, has two objectives: to show that the active nonlinear coupler laser is capable of creating soliton-like pulses even in the positive GVD regime, and to extend the model of the laser in the negative group velocity dispersion regime to include the effects necessary for pulse durations shorter than 100 fs.