Integrated circuits capable of sensing both infrared and visible images have been proposed. Until now, the usual practice for simultaneous imaging at both infrared and visible wavelengths in the same camera has involved splitting of the optical path into an infrared and a visible branch, each containing a separate image sensor optimized for its wavelength range. In contrast, each of the proposed image sensors would include pixel detectors for both wavelength ranges, and sensors could be designed to operate with or without splitting of optical paths.

The figure illustrates five alternative design concepts for the proposed image sensors. In the first and second concepts, the infrared- and visible-light pixel detectors would be segregated into adjacent subimage areas, necessitating splitting of the optical path. The first concept calls for enlargement of the silicon integrated-circuit multiplexer chip of a traditional infrared image sensor to accommodate a visible-light image sensor on the additional area. The second concept is similar to the first one, except that the visible-light detectors would be implemented in a hybrid structure. The visible-readout portion of the multiplexer circuitry could be similar to the infrared-readout portion, or it could be designed as a photoelectron-counting circuit.

Infrared- and Visible-Image Sensors would be integrated. Pixel detectors could be arranged in side-by-side subimages or else interspersed or superimposed in the same image area.

The third, fourth, and fifth concepts do not entail splitting of the optical path. According to the third concept, the visible and infrared pixel detectors would be interspersed throughout the same image area. The visible-image detectors could be of the complementary metal oxide/semiconductor (CMOS) active-pixel-sensor (APS) type. The infrared detectors could be of the thermopile or bolometer type. CMOS readout circuitry would be used for both sensors. The number of infrared pixels need not equal the number of visible pixels. The interspersion of infrared and visible pixels could be in any of a variety of patterns, depending on the requirements for spatial resolution in the infrared and visible images

The fourth concept calls for stacking of a monolithic visible-image sensor on top of a monolithic infrared-image sensor. The visible-image sensor would have to be made of silicon, because the infrared light could pass through a silicon-based sensor to the infrared detectors below. Registration of the infrared and visible pixel detectors could be achieved readily; however, whether or not they were registered, it would not be necessary to make them with equal pixel pitches. Wire bonds could be made between the two sensor chips to enable sharing of signals or sensor-fusion data processing on one or both chips. The fifth concept is similar to the fourth concept, except that the infrared sensor would be implemented in a hybrid structure.

This work was done by Eric Fossum and Bedabrata Pain of Caltech for NASA's Jet Propulsion Laboratory No further documentation is available. NPO-20209


NASA Tech Briefs Magazine

This article first appeared in the October, 1999 issue of NASA Tech Briefs Magazine.

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