Abstract: Optical filters capable of operating in the infra-red spectrum are disclosed. In one embodiment, a filter may be dynamically switched to provide one of two optical responses. One optical response may include the filter reflecting infra-red radiation across a range of wavelengths except at one or more wavelengths at which the filter absorbs the radiation. A second optical response may include the filter reflecting infra-red radiation across the entire range of wavelengths. In one embodiment, the switching may be caused by the physical displacement of a first filter component with respect to a second filter component. A method of switching the response of such a filter is also disclosed. Another embodiment of the filter may include one in which the optical response of the filter is effectively independent of either the incidence angle of the radiation impinging on it, or the polarization of the incident radiation.