A birefringent network can be formed from a pair of beam directing
elements that sandwich a birefringent filter. One of the beam director
elements can be a polarizing beam splitter and the other of the beam
director elements can be a reflector or polarizing beam splitter. The
polarizing beam splitters can be formed by an anisotropic material
sandwiched between two isotropic pieces and can include optical films to
couple both polarizations of light into and out of the beam splitters.
The polarizing beam splitters also can be formed by anisotropic material
on either side of an isotropic bow-tie piece, all of which is sandwiched
a pair of isotropic pieces. A birefringent network also can be formed by
a pair of bulk birefringent beam splitters sandwiching a birefringent
filter. Little or no polarization mode dispersion occurs in these
birefringent networks since all of the beams travel the same distances
through the same elements.