Inner quality of blue glass IR cut filter and use of blue glass lens

Digital camera use IR cut filter to ensure good image quality by filtering the infrared light otherwise detected by backside illuminated CMOS chips (with higher field of view). Due to the virtually angle-independent characteristics of filter glass from angle, blue glass is more and more used as IR cut filter. Pure interference filters have a high angle dependency and in addition reflect the IR light which can cause ghost images. In this presentation a typical design of a smart phone camera will be used to analyze the required quality of a blue glass absorption filter. The inner glass quality (e.g. striae) of blue glass as plano-plano filter will be examined. Striae are described as wavefront distortion and a recommendation for the inner glass quality of a blue filter glass will be elaborated. Furthermore a lens made out of blue glass (substituting the plano-plano filter) will be designed and analyzed. It turns out the blue glass lens can be used as a crown glass in an achromate shrinking down the size of the camera. The required transmittance curve will be calculated and a recommendation for the inner glass quality will be given.