Multifunctional collimator for contact image sensors

Disclosed is a cost-effective method to fabricate a multifunctional collimator structure for contact image sensors to filter ambient infrared light to reduce noises. In one embodiment, an optical collimator, includes: a dielectric layer; a substrate; a plurality of via holes; and a conductive layer, wherein the dielectric layer is formed over the substrate, wherein the plurality of via holes are configured as an array along a lateral direction of a first surface of the dielectric layer, wherein each of the plurality of via holes extends through the dielectric layer and the substrate from the first surface of the dielectric layer to a second surface of the substrate in a vertical direction.