Abstract: The invention discloses a comb wavelength division multiplexer, comprising: an input device at input side, a polarization splitter, a &lgr;/2 phase delay wave plate; a birefringent crystal filter; and a reflective parallel light polarization splitter for reflecting an incident light beam from the birefringent crystal filter into the birefringent crystal filter again, and passing the reflected light beam through the &lgr;/2 phase delay wave plate and the polarization splitter to an output side, so that the input side and the output side are a same side. The invention uses only one-stage filter to obtain a two-stage filtering effect. The channel isolation factor is improved and the size of the apparatus is reduced (FIG. 2).