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A cost-effective fiber laser architecture is introduced in which the output seed pulse is stretched and then returned in the oscillator for an additional single-pass amplification without spectral broadening. It is implemented in an all-PM-fiber configuration based on a Mamyshev oscillator with a low repetition rate of 1 MHz. It features a linear oscillator bounded by two offset chirped fiber Bragg gratings accompanied by a third one acting as a pulse recycling filter. The latter tailors the pulse profile in amplitude and phase to seed femtosecond chirped-pulse amplification systems without additional pre-amplification nor pulse stretching. A single-pump prototype generating 200-nJ, 100-ps pulses compressible to 290 fs at 1030 nm and at 960 kHz is demonstrated. Furthermore, simulations show how this new oscillator architecture can provide tailored seed pulses with high enough spectral energy density and low enough nonlinear phase to generate sub-200 fs, 40 µJ, > 180 MW pulses from an all-fiber setup involving a single tapered-fiber power amplifier, without pulse picking.

A femtosecond all-PM-fiber Mamyshev oscillator (MO) at 920 nm is presented. It is based on a neodymium-doped fiber with a W-type index profile that effectively suppresses the emission around 1064 nm. The linear cavity is bounded by two near-zero dispersion fiber Bragg gratings with Gaussian reflectivity profiles. The laser is self-starting and generates up to 10-nJ pulses at a repetition rate of 41 MHz. The pulses can be compressed to 53 fs with a grating-pair compressor. To our knowledge, this is the first Mamyshev oscillator and also the highest energy femtosecond fiber oscillator demonstrated in this spectral region.

We have developed a compact all-PM-fiber ytterbium-doped Mamyshev oscillator-amplifier laser system generating compressed pulses of 102 nJ and 37 fs, thus having over 2 MW of peak power, at a repetition rate of 52 MHz. The pump power from a single diode is shared between a linear cavity oscillator and a gain-managed nonlinear amplifier. The oscillator is self-started by pump-modulation and a linearly polarized single-pulse operation is achieved without filter tuning. The cavity filters are near-zero dispersion fiber Bragg gratings with a Gaussian spectral response. To our knowledge, this simple and efficient source has the highest repetition rate and average power among all-fiber multi-megawatt femtosecond pulsed laser sources and its architecture holds potential for generating higher pulse energies.