Abstract: An optical incremental shaft encoder in accordance with this invention involves an illumination source arranged to direct light through an optical slit, with the light then falling upon a series of very closely spaced lines forming a first grating. I have discovered that close by this grating a series of image planes are formed, with each plane containing multiple images of the slit. Generally, these images are distinct for distances of only 1/10th of an inch or less with respect to the grating or mask, and for the purpose of this invention, I do not use image planes further away from the mask or grating than this distance. I have found a way to utilize this diffraction phenomenon to great advantage by providing another grating-like member, placed at a selected one of the image planes, whose line spacing is identical to the image line spacing.

Abstract: A forward looking infrared system in which the usual FLIR is augmented by the addition of active laser illumination in order to enhance the FLIR's capability to discern in a scene certain details, such as manmade objects, especially under conditions of thermal washout. The laser is coded, and appropriate decoding electronics are provided to enable the FLIR to differentiate reflected laser radiation from thermal radiation of the scene. Therefore, it is unnecessary to endeavor to increase the brightness of the laser to an extent sufficient to overwhelm the natural thermal radiance level of the scene. Both types of radiation simultaneously impinge on a common detector, thereby eliminating the necessity for dual detectors and/or dual optics, and avoiding registration problems normally associated with the use of dual components.