Infra-red imaging system using a diffraction grating array

Abstract

In an infra-red imaging system, infra-red radiation from a scene is optically collected and directed to form an infra-red image of the scene on an array of bi-state diffraction grating elements. Each bi-state diffraction grating element has an activated state providing diffraction of incident infra-red radiation at a predetermined angle from the incident direction and an alternative inactivated state providing no such diffraction at the predetermined angle. Scanning apparatus sequentially activates the bi-state diffraction grating elements temporarily from their inactivated states to their activated states to produce a scanned infra-red image of the scene in IR radiation diffracted by the elements at the predetermined angle, which is collected and directed to an infra-red detector. The detector provides a coded electrical representation of the scanned infra-red image of the scene to further apparatus which generates therefrom a human-detectable signal. The separation of scanning from detection allows a single detector to be used for the detection of multiple pixels and thus reduces the size, complexity and cost of the detector apparatus. The scanning apparatus may also provide a chopping function by delaying the activation of each bi-state diffraction grating element to its activated state for a predetermined time period after a deactivation to the inactivated state of the previous sequentially activated diffraction grating element. The apparatus may combine IR radiation at two wavelengths by providing separate detectors at the angle of diffraction of each wavelength or by mixing diffraction grating elements of different grating pitch providing diffraction of each wavelength at the same angle to a single IR detector. Some embodiments may provide combination of IR and visible light for an enhanced visible image.