Continuum suppressed, uniformly repetitive 136fs pulse generation from an erbium-doped fibre laser with nonlinear polarisation rotation

A new type of femtosecond erbium-doped fibre laser with nonlinear polarisation rotation is presented, in which a polariser is installed at a point-symmetric position against a polarisation-sensitive optical isolator in the ring laser cavity. This technique enables us to remove the continuum (DC component) in the oscillation waveform completely and to obtain a stable pulse train as short as 136-145 fs with a 56 MHz repetition rate.