Multi-color infrared imaging device

• US 7,109,488 B2
• Filed: 02/26/2004
• Issued: 09/19/2006
• Est. Priority Date: 02/26/2004
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Milton, A. Fenner
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Rosenberger, Frederick F.
• Application Number:
  US10/787,907
• Publication Number:
  US 20050189492A1
• Time in Patent Office: 936 Days
• Field of Search: 250/332, 250/339.02, 250/370.08, 257/440, 257/443, 257/E27.138
• US Class Current: 250/332
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• CPC Class Codes: H01L 27/14621 Colour filter arrangements
• CPC Class Codes: H01L 27/14649 Infrared imagers
• CPC Class Codes: H04N 23/11 for generating image signals from visible and infrared light wavelengths
• CPC Class Codes: H04N 23/20 for generating image signals from infrared radiation only
• CPC Class Codes: H04N 25/131 including elements passing infrared wavelengths
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A multi-color IR imaging device includes optics that direct mid-wave infrared (MWIR) and long-wave infrared (LWIR) radiation onto a focal plane array having LWIR and MWIR detection layers. Pixel groups that include at least one first pixel and one second pixel are defined on the focal plane array, and a first filter and a second filter which form part of an inhomogeneous filter is placed over the respective first and second pixels in a checkerboard pattern, in close proximity to the detection layers. This allows MWIR radiation in M band, and LWIR radiation in an L₁ band to pass therethrough and illuminate the first pixels, and M, L₁, and a separate LWIR band designated L₂ to pass therethrough and illuminate the second pixels. To simultaneously image both MWIR and LWIR, the focal plane array is placed at a predetermined distance from the optics so that the MWIR spot size covers a single pixel and the LWIR spot size is about the same area as the area of a group of two first pixels and two second pixels. Since all pixels receive the M band, half of the pixels in the group receive the L₁ band, and the other half receives the L₂ band, three bands can be generated. This allows simultaneous imaging of MWIR and two sub-bands of the LWIR from the same point in space.

Claims

1. A multi-color infrared (IR) imaging device comprising:

a focal plane array for detecting both MWIR and LWIR, said focal plane array having at least a first set of pixels and a second set of pixels defining a pixel group, each of said sets of pixels having a pixel area, said pixel group having a pixel group area;

said first set of pixels further comprising a first pixel, a first pixel filter, a first stratum, a first MWIR detector layer and a first LWIR detector layer, said first pixel being coupled to an integrated circuit;

said second set of pixels further comprising a second pixel, a second pixel filter, a second stratum, a second MWIR detector layer and a second LWIR detector layer, said second pixel being coupled to said integrated circuit;

optics for simultaneously directing said MWIR and said LWIR in focus onto said focal plane array, said MWIR defining an M band, said LWIR defining an L₁ band and an L₂ band;

an inhomogeneous filter, comprising said first pixel filter and said second pixel filter, overlaid on the focal plane array so that said M band and said L₁ band pass through to said first set of pixels, and further said inhomogeneous filter passes said M band, said L₁ band and said L₂ band to said second set of pixels;

said optics establishing an MWIR spot size and an LWIR spot size, said focal plane array being spaced-apart from said optics by a predetermined distance chosen according to a focal length for said MWIR so that said MWIR spot size is about equal to said pixel area and said LWIR spot size is about equal to said pixel group area;

said first set of pixels generate a first pixel output that includes said L₁ band;

said second set of pixels generate a second pixel output that includes said L₁ band and said L₂ band;

a multiple amount of said first set of pixels and said second set of pixels being placed on said focal plane array; and

said first pixel outputs and said second pixel outputs generate a radiation map converted into a plurality of electric impulses read by said integrated circuit, said integrated circuit provides a high-resolution color infrared image to a means for display.

2. The device of claim 1 , further comprising:

said integrated circuit being a read-only integrated circuit board; and

said first MWIR detector layer, said first LWIR detector layer, said second MWIR detector layer and said second LWIR detector layer being grown by epitaxial techniques.

3. The device of claim 2 further comprising a means for isolating said L₂ band from said second pixel output.

4. The device of claim 3 wherein said isolating means is a differencing amplifier.

5. A device for simultaneous multi-color imaging MWIR and LWIR, comprising:

a focal plane array defining a plurality of pixels, said plurality being divided into a first set of pixels and a second set of pixels arranged in a checkerboard pattern, each of said sets of pixels having a pixel area;

said first set of pixels further comprising a first pixel, a first pixel filter, a first stratum, a first MWIR detector layer and a first LWIR detector layer, said first pixel being coupled to an integrated circuit;

said second set of pixels further comprising a second pixel, a second pixel filter, a second stratum, a second MWIR detector layer and a second LWIR detector layer, said second pixel being coupled to said integrated circuit;

optics for simultaneously directing said MWIR and said LWIR in focus onto said focal plane array;

an inhomogeneous filter, comprising said first pixel filter and said second pixel filter, overlaid on said focal plane array allowing said MWIR radiation and a first portion of said LWIR to pass through to said first set of pixels, and further allowing said MWIR and a second portion of the LWIR band to pass through to said second set of pixels;

said optics establishing an MWIR focal length and an LWIR focal length equal to said MWIR focal length, said focal plane array being spaced-apart from said optics by a predetermined distance chosen according to said MWIR focal length to establish an MWIR spot size about equal to said pixel area, and further to establish an LWIR spot size equal to a combined area of four adjacent pixels, wherein said LWIR spot size is incident on two pixels from said first set of pixels and two pixels from said second set of pixels;

said first set of pixels generate a first pixel output that includes an L₁band;

said second set of pixels generate a second pixel output that includes said L₁ band and an L₂ band;

a means for isolating said L₂ band from said second pixel output;

a multiple amount of said first set of pixels and said second set of pixels being placed on said focal plane array; and

said first pixel outputs and said second pixel outputs generate a radiation map converted into a plurality of electric impulses read by said integrated circuit, said integrated circuit provides a high-resolution color infrared image to a means for display.

6. The device of claim 5 wherein said inhomogeneous filter comprises a plurality of said first pixel filters and a plurality of said second pixel filters.

7. The device of claim 6 wherein said each of said first pixel filters corresponds to one pixel from said first set of pixels, and each of said second pixel filters corresponds to one pixel from said second set of pixels.

8. The device of claim 5 wherein said inhomogeneous filter comprises a plurality of first stripe filters and a plurality of second stripe filters.

9. The device of claim 8 wherein said first stripe filters and said second stripe filters correspond to alternating rows of said pixels.

10. A method for simultaneously imaging both MWIR and LWIR in multiple colors, comprising the steps of:

forming a first set of pixels with a first pixel, a first pixel filter, a first stratum, a first MWIR detector layer and a first LWIR detector layer, said first pixel being coupled to an integrated circuit;

forming a second set of pixels with a second pixel, a second pixel filter, a second stratum, a second MWIR detector layer and a second LWIR detector layer, said second pixel being coupled to said integrated circuit;

providing a focal plane array having said first set of pixels and said second set of pixels, said first set of pixels and said second set of pixels defining a pixel group, said first pixel and said second pixel each having a pixel area;

positioning optics for simultaneously directing said MWIR and said LWIR in focus onto said focal plane array;

overlaying an inhomogeneous filter, comprising said first pixel filter and said second pixel filter, on said focal plane array;

placing said first pixel filter between said first pixel and said optics to allow an M MWIR band and an L₁ LWIR band to pass through to said first set of pixels;

laying said second filter between said second pixel and said optics to allow said M band, said L₁ band and an L₂ LWIR band to pass through to said second set of pixels;

spacing said focal plane array apart from said optics by a predetermined distance corresponding to an MWIR focal length to establish an MWIR spot size about equal in size to said pixel area;

receiving a first pixel output and a second pixel output in said integrated circuit, said first pixel output including said L₁ band and said second pixel output including said L₁ band and said L₂band;

isolating said L₂ band from said second pixel output;

generating a radiation map from said first pixel output and said second pixel output;

placing a multiple number of said first set of pixels and said second set of pixels on said focal plane array;

converting said radiation map into a plurality of electric impulses read by said integrated circuit; and

displaying a high-resolution color infrared image on a means for display.

11. The method of claim 10 wherein:

said pixels define a pixel group with a pixel group area; and

said spacing-apart step establishes a LWIR spot size about equal to a pixel group area.