Unidirectional lasing using loss management in a reciprocal fiber ring laser
in: Temporal Proceedings (2021)
We report on the observation of a new phenomenon, occurring in a fiber ring laser. It describes the transition from an initially bidirectional emission of a fully reciprocal fiber ring laser to a unidirectional emission at a certain pump power threshold. In terms of the final direction, we observed that it is not predefined and appears to be probabilistic in nature every time the threshold is exceeded. Therefore, we term this new phenomenon as direction instability. In this paper we provide a first discussion of how the pump power threshold and the final direction can be influenced by the length and the linear propagation loss of the cavity.
We observed that the threshold follows a power times length scaling and is reduced for longer cavity lengths and lower propagation losses. This indicates that this phenomenon has a nonlinear origin. In terms of the final direction it was observed that the cavity tries to mitigate the losses and prefers the direction with minimal nonlinear loss. The nonlinear loss is mainly experienced due to stimulated Raman scattering occurring as a result of high circulating powers and km long cavity lengths. This opens the possibility to predefine a final direction through a loss imbalance between the two counter propagating directions. Using this a final direction can be predefined with up to 100 % certainty. We achieved the required loss imbalance by splicing different batches of the same Corning’s HI-1060 passive fiber in the ring cavity. Albeit the same manufacturer and fiber type, different fiber batches showed a very different loss profile in the guiding spectrum between 1-2µm.