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Optimizing mode instability in low-NA fibers by passive strategies

: Haarlammert, Nicoletta; Sattler, Bettina; Liem, Andreas; Strecker, Maximilian; Nold, Johannes; Schreiber, Thomas; Eberhardt, Ramona; Tünnermann, Andreas; Ludewigt, Klaus; Jung, Markus


Optics Letters 40 (2015), No.10, pp.2317-2320
ISSN: 0146-9592
Journal Article
Fraunhofer IOF ()

Systematic experimental investigations toward the mode instability (MI) threshold in low-NA fibers are performed. By testing several fibers with varying V-parameters drawn from the same preform, a high degree of reproducibility of the experimental conditions could be achieved. This allows for systematic investigations on isolated parameters influencing the complex behavior of MI. A maximum MI threshold of 2 kW could be demonstrated for the tested fibers, which represents a new record output power for narrow linewidth fiber amplifiers. The MI threshold was found to sensitively depend on the V-parameter for large V-parameters (> 2), but to be robust for smaller V-parameters. Furthermore, the fiber bending diameter and the seed excitation conditions were identified to sensitively influence the MI threshold.