Co-extruded multilayer polymer films for photonic applications

Co-extrusion through a series of layer-multiplying die elements enables the production of polymer films containing tens to thousands of layers with individual layer thicknesses from the micro- to the nanoscale. The use of polymers with different refractive indexes allows to fabricate, with a simple and inexpensive process, narrowband one-dimensional photonic crystals. Tunability of the photonic gap can be achieved by proper choice of the materials or of the dies, varying the contrast in refractive indexes or the number and thickness of the individual layers. The use of elastomeric polymers offers the opportunity to modify the UV–VIS spectral response of the 1-D photonic crystals simply by deformation of the film. Finally, co-extrusion of multi-layer polymeric films revealed to be an enabling technology, which allows the realization of new polymeric optical devices, going from flexible lasers to gradient refractive index lenses.