101.8 MHz and FWHM 62.5 nm spectrum in a NALM mode-locked polarization-maintaining fiber laser

Abstract

We propose and demonstrate a figure-nine polarization-maintaining fiber laser with a nonlinear amplifying optical loop mirror (NALM) as a fast saturable absorber. The oscillator includes a non reciprocal phase shifter, which can achieve low mode locking threshold and excellent self starting performance. The repetition frequency of the laser reaches 101.8 MHz. The signal-to-noise ratio of a single frequency is approximately 70 dB. The pulse duration of the laser is 80 fs. By employing cut-back techniques to accurately compensate for intracavity dispersion, we are able to achieve a flat and broad spectral output with a full width at half maximum (FWHM) of better than 62.5 nm at the center wavelength of 1584.4 nm. Thisrepresentsthe broad FWHM spectrum observed in all polarization-maintaining fiber NALM lasers.