The principle of design of polarization band_pass filters used for wavelength d ivision multiplexing systems is presented. The design method is based on the con cept of thin_film photonic crystal superlattice. Two kinds of design are put for ward. One of them is to construct by superposition of two photonic crystals; and the other is to insert a new photonic crystal into the middle of a photonic cr ystal, so that there are in effect three photonic crystals. Such band_pass filte rs have excellent optical properties with p_polarization transmittance and s_pol arization reflectance. The characteristics of the filters, including peak transm ittance, half_band width and rejection are discussed.