An external cavity laser system includes an in-line optical filter and a reflection suppressor that efficiently suppresses back-reflected light while allowing light to resonate within the laser cavity. The reflection suppressor may include a polarizer that polarizes light within the cavity and polarization rotators that rotate the polarization state of the polarized light such that back-reflected light is suppressed by the polarizer. Because back-reflected light is suppressed, use of an in-line filter becomes viable in an external cavity laser system.