  We demonstrate a fiber source with the best performance from an ultrafast
fiber oscillator to date. The ring-cavity Mamyshev oscillator produces 50-nJ
and 40-fs pulses. The peak power is an order of magnitude higher than that of
previous lasers with similar fiber mode area. This performance is achieved by
designing the oscillator to support parabolic pulse formation which enables the
management of unprecedented nonlinear phase shifts. Experimental results are
limited by available pump power. Numerical simulations reveal key aspects of
the pulse evolution, and realistically suggest that (after external
compression) peak powers that approach 10 MW are possible from ordinary
single-mode fiber. The combination of practical features such as environmental
stability, established previously, with the performance described here make the
Mamyshev oscillator extremely attractive for applications.
