We　demonstrate　an　erbium-doped　all-fiber　laser　mode-locked　by　means　of　nonlinear　polarization　evolution　in　polarization　maintaining　(PM)　fibers.　The　artificial　saturable　absorber　consists　of　a　piece　of　PM　active　fiber　and　a　Faraday　mirror　(FM)　in　combination　with　angle　splice.　The　birefringence　of　the　PM　fiber　is　compensated,　and　the　slope　of　transmission　curve　is　steepened　thanks　to　the　FM　and　the　active　fiber.　The　transmission　characteristics　demonstrate　that　the　active　fiber　is　a　crucial　factor　to　obtain　a　high　repetition　rate　ultrafast　laser.　We　study　and　discuss　channeled　spectra　caused　by　the　mechanisms　of　soliton-soliton　interaction　and　birefringence-induced　filter.　A　good　agreement　is　achieved　between　the　theoretical　analyses　and　experimental　results.