The present invention provides low cost methods and apparatuses for filtering out polarized light reflections in a free-space optical isolator. In one embodiment, a laser directs a non-polarized optical signal through a series of polarizers and rotators in order to isolate an optical signal having a specific polarization. The present invention also includes a quarter-wave plate placed in series with the rotators and polarizers, to help filter away reflections occurring while the signal passes through free space. The inclusion of the quarter-wave plate helps filter away a greater amount of near-end reflections from going back to the laser, even with the use of low cost polarizers. Accordingly, the present invention can polarize an optical signal more efficiently than with prior methods, and at a much lower cost.