Bidirectional mode-locked fiber ring laser using self-regenerative, passively controlled, threshold gating.

We demonstrate a technique to achieve bidirectional mode locking of a fiber ring laser using two amplitude modulators passively driven by a signal regenerated from the oscillation of the laser itself. The new scheme allows generation of two independent-frequency unlocked-countercirculating pulses and active control of their crossing points. The technique minimizes the effects of the dead band associated with crossing at a scattering media. Results show stable bidirectional pulses at a 5MHz repetition rate with no detectable dead band.