An apparatus for channel interleaving comprises a spatial birefringent device assembly and a reflector which is configured so as to direct light from the spatial birefringent device assembly back through the spatial birefringent device assembly. The spatial birefringent device assembly comprises at least one spatial birefringent device. Directing light from the spatial birefringent device assembly back through the spatial birefringent device assembly substantially mitigates cross-talk and/or dispersion of the apparatus for channel interleaving in communications.