We　demonstrate　an　all　fiber　mode-locked　ultrafast　erbium　laser　oscillator　by　means　of　nonlinear　polarization　evolution　(NPE)　in　polarization　maintaining　(PM)　fibers.　Here,　the　artificial　saturable　absorber　(SA)　is　formed　by　a　piece　of　PM　active　fiber　and　a　Faraday　mirror　(FM).　High　repetition　rate　could　be　obtained　thanks　to　the　introduction　of　the　PM　active　fiber.　The　transmission　characteristics　of　the　SA　are　studied　through　theoretical　analyses　as　well　as　experimental　demonstration.　Channeled　spectra　caused　by　soliton-soliton　interaction　and　birefringence-induced　filter　are　also　studied　and　discussed.　A　good　agreement　is　achieved　between　the　theoretical　analyses　and　experimental　results.