Ltv Aerospace & Defense Company

Vought Corporation

James D Billingsley

Dayton D Eden

Fergus E Moore

Donald T Cottingham

A dynamic infrared scene projector for presenting cinematic, two-dimensional, spatially distributed scene data to an infrared sensor is provided comprising programmable, thermoptic infrared modulators which exploit thermally-induced changes in the infrared optical properties of a thin film of vanadium dioxide. Because of a hysteresis in the vanadium dioxide material, a stored scene can be created in the modulators by scanning a focused modulated visible or near-infrared laser beam across the thin film while it is thermally biased in the hysteresis loop. The scene is projected into the sensor by placing the modulators between an infrared source/condenser system and a system of projection optics. Dynamic scene projection is accomplished by an erase/rebias system and an optical framing switch to yield a flicker-free output. Erasing of the optical modulator is accomplished by momentarily cooling the VO.sub.2 film to a temperature below the hysteretic loop. Rebiasing of the optical modulators is accomplished by reheating to increase the temperature of the thin film to a value not exceeding a thermal bias temperature.

Dynamic infrared scene projector

An optical processing system for processing infrared information prior to detection. In one embodiment, optical information from an infrared scene is focused by optics (10) onto a thermoptic modulator (12) which contains an optical structure (16) disposed on the faceplace of a cathode ray tube. The modulator is normally nonreflective of infrared energy from the scene incident thereon. Reflecting spots (22) written on the modulator by an electron beam reflect a portion of the scene to a detector (52) which generates a signal representative of the radiance of the scene element sampled. A series of first and second reflecting spots of different size are written at selected coordinates on the modulator. The respective signals generated by the detector for each spot of the pair are subtracted to provide a spatial band pass filtered signal for each sampling coordinate on the modulator. Scanning of an entire array of sampling locations provides spatially filtered scene information in which relatively high and low spatial frequency components have been eliminated, thereby improving the contrast between an object in the scene and the background.

Predetection processing of optical information

The specification discloses a method and apparatus for stabilizing images in the reference frame of a forward or down looking infrared receiver moving relative to the scene. An infrared modulator (14) is disposed in the image plane of the receiver for imaging infrared energy from the scene. The modulator (14), normally nonreflecting of infrared energy incident thereon, is capable of having reflective spots written on selected locations thereon to reflect infrared energy incident at those locations. Detectors (24) positioned to detect infrared energy reflected from the modulator provide an output signal representing the radiance values of the sampled scene element. A microprocessor (30) is connected to the detector, responsive to the detected output signal, to detect image motion caused by relative motion between the receiver and the scene from the detected information. The microprocessor (30) provides transform information about the transformation from reference frame to modulator coordinates such that infrared energy reflected from the modulator will appear stabilized to a sampling frame in the computer during relative motion between the telescope and the scene. Interface electronics (32) connected to the microprocessor (30) converts selected sampling points in the window frame coordinates to modulator coordinates at which coordinates an electron gun (21) writes reflective spots on the modulator.

Image motion and distortion stabilization for predetection scene

A dark field infrared telescope. Energy from an infrared scene is focused by a lens (10) onto a thermoptic modulator (12) comprising an optical structure (16) containing a thin film of vanadium dioxide disposed to form the faceplate of a conventional cathode ray tube. The modulator, normally nonreflecting of infrared energy, may have reflecting spots written at selected coordinates thereon by an electron beam from the cathode ray tube. A reflecting spot written on the modulator optically couples a selected element of the scene imaged on the modulator to an infrared detector (52) maintained at low temperature. A retroreflecting mirror (30), cold spectral filter (46), field lens (47), cold field stop (48) and cold pupil stop (50) are provided ahead of the detector to produce a low background flux cavity with the detector at one end and the retroreflecting mirror at the other. In its unswitched state, the modulator is nonreflecting and the scene image is not coupled to the detector. The cold detector thus looks back upon itself and sees a 'dark field.' Under the control of the sensor microprocessor (22), the electron beam is synchronously switched on and off to modulate the detector signal. The detector signal is then synchronously demodulated by a signal processor (56) to reduce the noise of the detector and preamplifier. By reducing background flux and detector noise, the sensor approaches a signal shot noise or electronic noise limited condition.

Growing community of inventors

Arlington, TX, United States of America

James D Billingsley