Visible and infrared dual mode imaging system

1. An imaging system, comprising:

an aperture for receiving incident light;

an image sensor for capturing image data in response to the incident light; and

an optical filter disposed between the aperture and the image sensor, wherein the optical filter includes a dual window transmission spectrum, the dual window transmission spectrum including:

a first pass band aligned to pass visible light; and

a second pass band overlapping with an absorption band of infrared light in Earth's atmosphere,

wherein the optical filter comprises a single optical filter element including both the first and second pass bands such that a single ray of light incident on the single optical filter element is subject to both the first and second pass bands at a given time.

2. The imaging system of claim 1 , wherein the optical filter substantially blocks infrared light outside of the second passband.

3. The imaging system of claim 1 , wherein the optical filter comprises a multi-layer thin film interference filter.

4. The imaging system of claim 1 , wherein the imaging system comprises a surveillance camera, the imaging system further comprising:

an infrared light source to generate infrared light having a wavelength that falls within the second pass band.

5. The imaging system of claim 2 , wherein the second passband is non-overlapping with the first passband.

6. The imaging system of claim 4 , further comprising:

a logic unit coupled to the infrared light source to enable the infrared light source during nighttime and to disable the infrared light source during daytime.

7. The imaging system of claim 5 , wherein the second passband is approximately centered within the absorption band of infrared light in Earth's atmosphere and has a width equal to or less than the absorption band of infrared light in the Earth's atmosphere.

8. The imaging system of claim 6 , further comprising:

a lens disposed between the aperture and the optical filter; and

a daylight sensor coupled to the logic unit to enable the logic unit to determine whether a current time is the daytime or the nighttime.

9. The imaging system of claim 7 , wherein the second passband overlaps 950 nm and the width of the second passband is approximately 50 nm.

10. An apparatus, comprising:

a pixel array for capturing image data in response to incident light, the pixel array including a repeating pattern of macropixels, wherein each macropixel includes multiple color pixels for capturing a visible spectrum image and an infrared pixel for capturing an infrared image; and

a multi-layer optical filter array disposed over the pixel array, the multi-layer optical filter array including:

an infrared filter layer for filter infrared light; and

a color filter array layer including a repeating pattern of color filter elements for filtering different colors of visible light,

wherein the infrared filter layer comprises a blanket filter layer overlaying the pixel array and covering both the color pixels and the infrared pixel of each macropixel, and wherein the infrared filter layer includes:

a first pass band aligned to pass visible light; and

a second pass band overlapping with an absorption band of infrared light in Earth's atmosphere to permit light falling within the absorption band of infrared light in Earth's atmosphere to pass through the multi-layer optical filter array to the pixel array,

wherein the second pass band overlaps 950 nm and has a width equal to or less than the absorption band of infrared light in the Earth's atmosphere.

11. The apparatus of claim 10 , wherein the infrared filter layer substantially blocks infrared light outside of the second pass band and wherein the second pass band is non-overlapping with the first pass band.

12. The apparatus of claim 10 , wherein the infrared filter layer comprises a multi-layer thin film interference filter.

13. An apparatus, comprising:

a pixel array for capturing image data in response to incident light, the pixel array including a repeating pattern of macropixels, wherein each macropixel includes multiple color pixels for capturing a visible spectrum image and an infrared pixel for capturing an infrared image; and

a multi-layer optical filter array disposed over the pixel array, the multi-layer optical filter array including:

an infrared filter layer for filter infrared light; and

a color filter array layer including a repeating pattern of color filter elements for filtering different colors of visible light,

wherein the infrared filter layer includes:

a first portion aligned with the color pixels to block the infrared light and pass the visible light, wherein the first portion comprises an infrared cut filter; and

a second portion aligned with the infrared pixel to pass the infrared light, wherein the second portion of the infrared filter layer comprises a clear element.

14. A method of operating a dual mode imaging system, comprising:

receiving light at an optical filter having a dual window transmission spectrum, the dual window transmission spectrum including a first pass band aligned to pass visible light and a second pass band approximately equal to and limited by an absorption band of infrared light in Earth's atmosphere;

during daytime, passing the visible light through the first pass band to an image sensor while blocking the infrared light falling outside of the second pass band; and

during nighttime, passing the infrared light through the second pass band to the image sensor.

15. The method of claim 14 , wherein the second passband is non-overlapping with the first pass band.

16. The method of claim 15 , wherein the second pass band is approximately centered about 950 nm and has a width of approximately 50 nm.