Abstract
A normal dispersion fiber oscillator with 30-m-long erbium-doped gain fiber was demonstrated in different operation modes. The highest pulse energy and the broadest spectral width were 33 nJ and 60 nm (centered at 1568 nm and 1579 nm), respectively. The output pulses of high-energy and broad-bandwidth modes were compressed to the corresponding Fourier transform limits by an ultrashort pulse shaper, achieving 150.5 fs and 116.4 fs, respectively. On the other hand, a double-pass grating pair compressed the 33 nJ pulse to 155.8 fs with 36% throughput. This would enable a record peak power of 47 kW (for erbium-doped fiber oscillators) if the pulse train is free of undesired sub-pulses or background. We also investigated the pulse train quality by a series of experiments, such as second-harmonic generation, long-range intensity autocorrelation, and radio-frequency spectrum measurement, showing that the high-energy pulse train could be subject to significant sub-pulses or background noise. A cleaner pulse train could be obtained at lower pump power by changing the intracavity polarization states.