Discrete evolution on temporal separation and phase difference for bound solitons in an Yb mode-locked fiber laser*

Multiple pulse regime is a common feature in passively mode-locked fiber lasers (MLFL). They could either be equally spaced, randomly distributed or arranged in a state of close interacting pulses. The later is often called bound solitons and presents strong modulation in the optical spectrum, which contains information about average relative phase, Δφ, and temporal separation between the pulses, τ. In this work, we study how increments in the total intracavity energy act on τ and Δφ for an Yb MLFL. For this, we continuously monitored the optical spectrum and the autocorrelation as the pump power was increased. We observed a discrete nature of τ, which is in agreement with previous works that observed its quantization for Er-doped fiber lasers [1] and predicted the quantization of binding energy between bound solitons [2]. Our work provides a systematic experimental study capable of capturing the jumps in τ, besides reporting a discrete behavior that is also present in Δφ.

[1] J. M. Soto-Crespo, N. Akhmediev, Ph. Greluand F. Belhache, Opt. Lett. 28, 1757-1759 (2003).
[2] A. Komarov, K. Komarov and F. Sanchez, Phys. Rev. A 79, 033807 (2009).