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Influencing Unidirectionality Threshold and Final Direction by Loss Management in a Reciprocal Fiber Ring Laser

In a recent manuscript we reported for the first time the occurrence of unidirectional lasing at full laser operation without any directional elements in a high-power reciprocal all-fiber ring laser [1] . The setup is shown in Fig. 1 . The cavity is pumped by a pump diode ( PD ) with an emission wavelength of 976 nm. The pump power enters the ring by a pump signal combiner (PSC) and reaches a 6 m long Yb-doped active fiber section (Yb). Here a bidirectional laser signal at around 1100 nm is emitted. The active fiber is followed by a long (~ km) passive fiber-Corning HI1060 (Ge). Finally, an output tap coupler (OC) with a low nominal out-coupling ratio of either 0.01%, 0.1% or 1% at 1060 nm design wavelength feeds most of the signal back to the PSC where it passes through the ring again, and a small part of the signal out of the cavity. As no optical isolator is included in the ring cavity, clockwise and counter clockwise signals can propagate starting at the laser threshold.