Besides dielectric and metallic materials we are using amorphous silicon as high index material for applications in the NIR starting from ~820nm. The high refractive index allows designs and optical properties not accessible for standard dielectric materials.
To coat plastic substrates, special cold and low-stress processes have been developed. For example, it is possible to produce filters with a thickness of >5 µm on Zeonex™ with excellent adhesion and stability properties.
Another example is the hydrophobic TopFlex™ coating.