Infrared filter commonly refer to filters that reflect or block mid-infrared wavelengths while passing visible light. It is applied in wide range of fields that use camera module: surveillance system, vehicle cameras, camcorder, smartphone, etc. Infrared filters can be designed in bandpass, longpass, and shortpass configurations for applications in the SWIR, NIR, and MIR wavelength bands.
Infrared silicon filter normaly used for 3-5um. We can achieve low absorption at 9um wavelength by float zone silicon material.