We review our recent works on the realization of planar lightwave circuit (PLC) technology-based optical interleavers. Commercially available polymer materials were used to fabricate the devices and we implemented our designs using two different configurations. The first is based on a folded two-stage-cascaded Y-junction MZI interleavers which offers a flat-top 100 GHz channel spacing over the entire C-band. The second is based on a three-dimensional structure which allows selectable channel spacing and adjustable flat-top using thermooptic effect. This interleaver is made of two waveguides laid in two different but parallel layers.