Full-power isolation test of unidirectional ring-cavity operation

Conduct a like-for-like full-power comparison of the same ring cavity with and without the intracavity isolator, using a higher-power band-pass filter to isolate the effect of unidirectional operation on the high-frequency relative intensity noise.

Background

The experiments show substantially lower high-frequency RIN for the unidirectional ring-seeded MOPA than for the bidirectional FBG-seeded MOPA. The authors attribute this advantage potentially to the avoidance of standing-wave spatial hole burning and the reduction of feedback-induced mode coupling, but the present setup cannot isolate the effect of the intracavity isolator at the relevant power level.

Removing the isolator would double the intracavity power and exceed the approximately 2 W power limit of the existing band-pass filter. Consequently, bidirectional operation is possible only at approximately 1 W, which would not provide a like-for-like comparison with the high-power measurements. A higher-power filter is therefore required for the unresolved full-power test.

References

A more direct test would compare the same ring cavity with and without the intracavity isolator, isolating the effect of unidirectional operation alone. This was not possible in our system because removing the isolator doubles the intracavity power and exceeds the $\sim$2~W limit of the band-pass filter, restricting bidirectional operation to $\sim$1~W; such a low-power comparison would not be like-for-like, and a full-power test using a higher-power filter is left to future work.

— RF-Resolved RIN Engineering of High-Power CW Yb Fiber Laser Architectures Using Seed Topology, Seed Power, Pumping Geometry and Cavity FSR  (2610.11856 - Augustine et al., 8 Oct 2026) in Section III, subsection “Comparison of All Architectures”