Sensor for dual wavelength bands

A dual wavelength focal plane has a first array of infrared sensing pixel elements and a second array of visible light pixel elements adapted to be selective to colors encountered while driving an automobile. The second array is selective to the colors red, blue and green, so being selective to traffic control signals, including brake lights of other automobiles. The arrays are vertically stacked on a monolithic silicon substrate. The arrays are electrically coupled to a processor and display to integrate the infrared and color pixel elements into a view for a driver of the automobile.

FIELD OF THE INVENTION

The present invention relates to sensors, and in particular to a sensor for at least two wavelength bands such as infrared and visible color wavelengths.

BACKGROUND OF THE INVENTION

Microbolometer arrays are arrays of IR sensors used to sense infrared (IR) light. The sensors are formed in an array on a semiconductor substrate in a well known manner. IR light is focused on the array via optics. When coupled to a display, the microbolometer array provides a heat based (IR) image, such as currently used in some automobiles to provide night vision to a driver. These have been extremely useful for providing visual images of humans and other animals well before they can be seen by the eye with the aid of headlights.

One problem associated with such displays is that they do not show other information which is required for safe driving, such as traffic control lights. The display may show whether a light is on or off by the heat that it generates, but the heating effect is slow and hence is not a reliable indication. Thus, there is no way to safely determine the color of the light. It should be noted that some states allow lights to be positioned horizontally. Remembering which side of the light is red may be difficult for many drivers.

SUMMARY OF THE INVENTION

A dual wavelength focal plane has a first array of infrared sensing pixel elements and a second array of visible light pixel elements adapted to be selective to colors encountered while driving an automobile. The second array is selective to the colors red, blue and green, corresponding to traffic control signals, including brake lights of other automobiles.

In one embodiment, the first and second arrays are fabricated on a monolithic silicon substrate. The arrays are electrically coupled to a processor and display to integrate the infrared and color pixel elements into a view for a driver of the automobile.

In a further embodiment, the second array comprises sets of three silicon photodiodes adapted to be selective to red, blue and green respectively, each set of photodiodes formed on the silicon substrate beneath the infrared sensing pixel element.

A heads up display for enhancing visibility for night time drivers of vehicles is provided by sensing infrared radiation sources generally in the path of the vehicle, selectively sensing visible radiation corresponding to traffic control colors, and combining the sensed visible radiation and infrared radiation to provide images for the heads up display. The traffic control colors are displayed in color.

In still a further embodiment, a CCD array is used as the second array for sensing visible light. The processor then utilizes digital filtering to separate out red, amber and green traffic control colors and superimposes those on the image from the infrared sensing array.

DETAILED DESCRIPTION OF THE INVENTION

A single monolithic un-cooled silicon focal plane is shown generally at110inFIG. 1. The focal plane is capable of imaging both infrared (IR) and visible wavelengths. One pixel is shown inFIG. 1. The pixel is formed on a silicon substrate115, and comprises a infrared-sensitive pixel135and a plurality of visible-light photosensors120,125and130, corresponding to selected colors. A filter is provided for each photosensor as indicated at122,127and132, to make the photosensors sensitive to certain colors, such as red, blue and green light bandwidths respectively. Such bandwidths generally correspond to vehicle traffic control signals. Vehicles include for example, automobiles, trains, boats and airplanes, as well as other vehicles. The photosensors may be made selective to other colors as desired.

In one embodiment, a single visible photosensor is fabricated with each bolometer pixel, and only red light is allowed to fall onto the array, by means of a red filter in the optical path.

A microbolometer135is formed above the photosensors and separated therefrom by a thermally-isolating space. The microbolometer may be formed in many different ways as shown in the art, but with minimal metalization to enhance transmission of visible light to the underlying visible photosensors. When formed in this manner, the microbolometer and photosensors are vertically stacked on a monolithic silicon substrate. The arrays are vertically integrated into an monolithic silicon substrate to optimize fill factor.

A system for providing a heads up display is shown inFIG. 2. An array of pixels comprising the focal planes ofFIG. 1are shown in a partial cutaway block representation at210. Connections to each of the sensors in each pixel are represented at215, and are made in any of many well known manners. The connections215are coupled to a processor220. Processor220is formed in the same substrate as the array of pixels in one embodiment, or may be an independent processor. Processor220processes the inputs from the array210to combine the IR monochrome image signals with the photosensor color signals to provide an image for display by display230, such as a common heads up display. The processor may also be integrated into display230. The display230provides a monochrome image corresponding to the IR signals, overlaid with colors provided by the photosensors.

By sensing IR sources generally in the path of the vehicle, selectively sensing visible radiation corresponding to traffic control colors, and combining the sensed visible radiation and infrared radiation to provide images for the heads up display, traffic control colors are displayed in color over a monochrome representation of the sensed IR.