50 nJ 250 fs all-fibre Raman-free dissipative soliton oscillator

The regime of highly chirped dissipative solitons is a powerful technique for generating high-energy femtosecond pulses. In this letter we demonstrate a successful scaling of the pulse energy in the all-normal-dispersion all-fibre configuration by increasing the cavity length and the mode-field diameter of the fibre simultaneously. Using a PM fibre of 10 mkm core diameter, it appears possible to lengthen the cavity up to 40 m, thus generating highly chirped pulses with energy above 50 nJ, whereas further growth is limited by the Raman effect. We have also found that the Raman threshold and compressed pulse duration strongly depend on the bandwidth of the intracavity spectral filter. The threshold length is increased by a reduction of the filter bandwidth at the expense of larger compressed pulse duration (250 fs instead of 150 fs). Further energy upscaling by means of core enlargement is shown to be possible, but for that one should waive the all-fiber design, or use custom-made fibre components.