New effects at cavity lengthening of an all-fiber dissipative-soliton oscillator

It is known that dissipative solitons (DS) generated in fiber oscillators lose their stability at cavity lengthening. We report on the experimental realization of the DS oscillator with increased cavity length (L~100 m). Stable operation is achieved in the all-fiber configuration consisting of a short single-mode-fiber (providing mode locking via nonlinear polarization evolution) and a long PM-fiber (providing formation of highly-chirped DSs) parts. We have identified the next limiting effect related to the onset of Raman conversion of the DS spectrum. The maximum output energy obtained with 5.5-μm-core PM-fiber amounts to ~30 nJ in 30-70 ps pulses externally dechirped to 200-300 fs at repetition rate ≥1.7 MHz. At that, the Stokes pulse reaching comparable energy inside the cavity does not break the soliton stability, surprisingly. The obtained results are analyzed using a simple model. Higher DS energy is shown to be possible by means of a PM fiber core enlargement.