IMAGING SYSTEM

• US 20090020714A1
• Filed: 02/06/2007
• Published: 01/22/2009
• Est. Priority Date: 02/06/2006
• Status: Active Grant

• Current Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Slinger, Christopher William
• Granted Patent: US 7,923,677 B2
• Time in Patent Office: Days
• US Class Current: 250/550
• CPC Class Codes: G01T 1/295 using coded aperture devices, e.g. Fresnel zone plates handling of radiation of particles, e.g. using diaphragms, collimators, diffraction G21K1/00
• CPC Class Codes: G02B 2207/129 Coded aperture imaging
• CPC Class Codes: G02B 27/4205 having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
• CPC Class Codes: G02B 27/4294 in multispectral systems, e.g. UV and visible
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof

Abstract

The present invention relates to an imaging system which employs the same principles as coded aperture imaging. High angular resolution coded aperture imagers require a small aperture size and relatively large spacing between the coded aperture array and the detector. At such high resolutions diffraction effects can start to dominate and can degrade image quality. The present invention provides a detector array which receives radiation from a scene via a coded diffractive mask. The coded diffractive mask is designed such that its diffraction pattern at the waveband of interest is a well conditioned coded intensity pattern having a strong autocorrelation function with low sidelobes. Thus radiation reaching the detector array is diffracted by the diffractive mask but in a defined way and it is the diffraction pattern of the mask which provides the coding. The scene image can then be reconstructed using the same techniques as for conventional coded aperture imaging but using the diffraction pattern of the mask as the aperture function. The coded diffractive mask may be a binary or greyscale mask, may operate in reflection or transmission and may be an amplitude or phase modulating mask.

Claims

1. A coded imager comprising a detector array arranged to receive, in use, radiation from a scene through a coded diffractive mask.

2. A coded imager as claimed in claim 1 wherein the coded diffractive mask produces a diffraction pattern on the detector array that is a well conditioned coded pattern at the waveband of operation.

3. A coded imager as claimed in claim 1 further comprising a processor for applying a decoding algorithm to the intensity pattern on the detector array so as to reconstruct a scene image.

4. A coded imager as claimed in claim 1 wherein the diffractive mask is one of a binary amplitude mask, an analogue amplitude masks, a binary phase modulating masks and an analogue phase modulating masks.

5. A coded imager as claimed in claim 1 wherein the coded diffractive mask is one of a reflective and a transmissive mask.

6. A coded imager as claimed in claim 1 wherein the coded diffractive mask is provided by a reconfigurable coded diffractive mask means.

7. A coded imager as claimed in claim 1 wherein the detector array has a narrow wavelength range of operation.

8. A coded imager as claimed in claim 1 further comprising one or more optical elements located in the optical path of radiation reaching the detector array.

9. A coded imager as claimed in claim 8 wherein at least optical element is located in the optical path between the coded diffractive mask and the detector array.

10. A coded imager as claimed in claim 1 wherein multiple diffractive coding masks are used simultaneously.

11. A coded imager as claimed in claim 1 further comprising at least one filter means.

12. A coded imager as claimed in claim 7 wherein the passband of the filter means can be changed.

13. A coded imager as claimed in claim 12 wherein the passband of the filter is adapted to be changed at least one of periodically, aperiodically and in response to a control signal.

14. A coded aperture as claimed in claim 12 wherein the apparatus is adapted to provide a different coded diffractive mask for a different passband of the filter means.

15. A method of coded imaging comprising the steps of arranging a detector array to receive radiation from a scene via a mask means, wherein the mask means comprises a coded diffractive mask that projects a well conditioned diffraction pattern onto the detector array.

16. A method as claimed in claim 15 further comprising the step of decoding the intensity pattern on the detector array to reconstruct an image of the scene.

17. A method as claimed in claim 15 further comprising the step of periodically reconfiguring the coded diffractive mask so as to provide at one of a different field of view and a different resolution.

18. A method as claimed in claim 15 further comprising reconfiguring the coded diffractive mask to provide a mask optimised for a different waveband of incident radiation.