Controlling Directionality and Threshold Powers in a Fully Reciprocal but Unidirectional Fiber Ring Laser.

Unidirectional lasing was recently demonstrated in a reciprocal all fiber ring laser. Here we characterize the factors controlling the required threshold and directionality of the laser. The factors include the linear and nonlinear propagation losses, which can be controlled to predefine the directionality and reduce the required threshold powers.