We investigated the behavior of a fiber-ring polarization-maintaining passively mode-locked ytterbium-doped laser in a broad range of dispersion values; i.e. from highly net-normal to net-anomalous, with a special emphasis near the zero of chromatic dispersion. Different lengths of an ad hoc polarization-maintaining photonic crystal fiber were used as intracavity dispersion compensator to shift the operation of this laser from net-normal to the net-anomalous regime. The laser generated the shortest light pulses around the zero of dispersion: 6 ps/7ps for-0.023 ps(2)/0.045 ps(2); in both cases, pulses were not transform-limited, being theoretically possible an out-of-cavity recompression down to 170 fs/220 fs, respectively. In the net-normal regime, we obtained a stable, ultra-low frequency, emission at 1.19 MHz, with pulses with a FWHM of 162 ps and pulse energy of 115 pJ. This laser presents a somewhat symmetrical behavior at both sides of the zero of dispersion thanks to its simple filter-free configuration. The laser is also environmentally robust, insensitive against temperature variations and mechanical vibrations, due to its integrated all-polarization-maintaining design.
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