As the demand for ultrafast radiation sources rises in a variety of fields, mode-locked fibre lasers could offer easy-to-implement, low-cost, compact solutions if their usual power limitations in the femtosecond regime were to be overcome. Recently we showed  that peak powers in excess of 600 kW were achievable using a femtosecond mode-locked ring fibre laser operating in the telecom C-band. The keystone behind this breakthrough was a novel polarization-insensitive InN-based semiconductor saturable absorber mirror (SESAM), tolerant to extremely high fluences (>1 TW/cm2) . In this paper we explore the limits of InN-SESAM-based ring lasers in terms of cavity length and achievable output power, demonstrating the possibility to attain output peak powers in excess of 1 MW, without the need for an external pulse amplification stage.
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