WAVEFRONT COMPENSATION IN OPTICAL SYNTHETIC APERTURE IMAGING PROCESSORS

• US 20130176167A1
• Filed: 09/29/2010
• Published: 07/11/2013
• Est. Priority Date: 09/29/2010
• Status: Active Grant

• Current Assignee: Institut national d'optique
• Original Assignee: Institut national d'optique
• Inventors: Bergeron, Alain, Marchese, Linda, Doucet, Michel
• Granted Patent: US 9,261,594 B2
• Time in Patent Office: Days
• US Class Current: 342/25.F
• CPC Class Codes: G01S 13/9005 with optical processing of the SAR signals
• CPC Class Codes: G01S 15/8904 using synthetic aperture techniques
• CPC Class Codes: G01S 15/8997 using synthetic aperture techniques
• CPC Class Codes: G01S 17/90 using synthetic aperture techniques
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: G02B 27/0087 Phased arrays
• CPC Class Codes: G02B 27/58 Optics for apodization or superresolution; Optical synthetic aperture systems
• CPC Class Codes: G02F 2203/12 spatial light modulator
• CPC Class Codes: G03H 2001/0224 Active addressable light modulator, i.e. Spatial Light Modulator [SLM] corresponding details, see subgroups of G03H2225/00

Abstract

There is provided a System and method of wavefront compensation in a synthetic aperture imaging system. A return signal data representative of a signal reflected by a target area to be imaged is received. A compensation phase figure corresponding to a wavefront compensation to be applied is provided. The compensation phase figure is added or otherwise applied to the phase pattern of the return signal data in order to obtain a compensated phase pattern. An optical beam is spatially modulated according to the compensated phase pattern to produce a modulated optical beam such that the compensation phase figure produces a wavefront compensation on the optical beam. An image of the target area is optically generated using the modulated optical beam.

Claims

1. A method for optically processing signal data in a synthetic aperture imaging system, the method comprising:

receiving return signal data representative of a signal reflected by a target area to be imaged, said signal data comprising an amplitude pattern and a phase pattern;

providing a compensation phase figure corresponding to a wavefront compensation to be applied;

applying said compensation phase figure to said phase pattern of said return signal data in order to obtain a compensated phase pattern;

spatially modulating an optical beam according to said compensated phase pattern to produce a modulated optical beam, said compensation phase figure producing a wavefront compensation on said optical beam; and

optically generating an image of said target area using said modulated optical beam.

2. The method as claimed in claim 1, wherein said applying comprises numerically adding said compensation phase figure to said phase pattern of said return signal data.

3. The method as claimed in claim 1, wherein said spatially modulating comprises addressing a plurality of pixels of a spatial light modulator with said compensated phase pattern to display said compensated phase pattern on said spatial light modulator to spatially modulate a phase of said optical beam accordingly.

4. The method as claimed in claim 1, wherein said providing a compensation phase figure comprises:

i) receiving calibration return signal data corresponding to a known reference image, said calibration return signal data comprising an amplitude pattern and a phase pattern;

ii) defining a plurality of sections on said spatial light modulator;

iii) selectively addressing part only of said sections with said phase pattern of said calibration return signal data to spatially modulate said optical beam and produce a calibration modulated optical beam;

iv) receiving a calibration image optically generated using said calibration modulated optical beam;

v) estimating a phase compensation corresponding to said part of said sections from said calibration image and said known reference image; and

vi) repeating steps iii), iv) and v) with other parts of said sections to provide said compensation phase figure using a combination of estimated phase compensations.

5. The method as claimed in claim 4, wherein said part comprises a reference section and an evaluated section and said calibration image comprises an interference pattern.

6. The method as claimed in claim 5, wherein said phase compensation is estimated by evaluating a phase shift in said interference pattern relative to said known reference image.

7. The method as claimed in claim 5, wherein a slope of said phase compensation within said evaluated section is estimated by evaluating an asymmetry of an intensity distribution in said interference pattern.

8. The method as claimed in claim 4, wherein said part comprises a single section and said phase compensation is estimated by evaluating a shift of a center of intensity of said calibration image relative to a reference point.

9. The method as claimed in claim 4, wherein said known reference image corresponds to a point target.

10. The method as claimed in claim 4, further comprising:

inputting a position of a known calibration target on the ground which corresponds to said known reference image;

acquiring said calibration return signal data from said known calibration target using a synthetic aperture acquisition unit; and

whereby said method compensates for a parameter variation in at least one of an optical signal processor used for said optically generating an image and said synthetic aperture acquisition unit.

11. The method as claimed in claim 1, wherein said method compensates for an absence of an optical element that is being eliminated from an optical synthetic signal processor used for said optically generating an image.

12. The method as claimed in claim 1, further comprising spatially modulating said optical beam according to said amplitude pattern of said return signal data to produce said modulated optical beam as modulated in phase and amplitude;

and wherein said optically generating an image of said target area is performed using said modulated optical beam as modulated in phase and amplitude.

13. The method as claimed in claim 3, wherein said return signal data comprises a two-dimensional return signal pattern, one dimension of said signal pattern corresponding to range data and the other dimension of said signal pattern corresponding to azimuth signal history;

and wherein said pixels are arranged in a two-dimensional array, one dimension corresponding of said array to said range data and the other dimension of said array corresponding to said azimuth signal history.

14. The method as claimed in claim 1, wherein said signal comprises a radar signal.

15. A system for optically processing signal data in a synthetic aperture imaging system, the system comprising:

an input for receiving a return signal data representative of a signal reflected by a target area to be imaged, said signal data comprising an amplitude pattern and a phase pattern;

a control unit having an addition module for adding compensation phase figure corresponding to a wavefront compensation to be applied to said phase pattern of said return signal data in order to obtain a compensated phase pattern; and

an optical signal processor comprising;

a light source for generating an optical beam having a wavefront;

a spatial light modulator for spatially modulating said optical beam according to said compensated phase pattern to produce a modulated optical beam, said compensation phase figure producing a wavefront compensation on said optical beam; and

focusing optics for optically generating an image of said target area using said modulated optical beam.

16. The system as claimed in claim 15, further comprising a compensation calculator for calculating said compensation phase figure corresponding to said wavefront compensation to be applied.

17. The system as claimed in claim 1516, wherein said spatial light modulator comprises a plurality of addressable pixels controlled according to said compensated phase pattern to display said compensated phase pattern on said spatial light modulator to spatially modulate a phase of said optical beam accordingly.

18. The system as claimed in claim 17, wherein said return signal data comprises a two-dimensional return signal pattern, one dimension of said signal pattern corresponding to range data and the other dimension of said signal pattern corresponding to azimuth signal history;

and wherein said pixels are arranged in a two-dimensional array, one dimension of said array corresponding to said range data and the other dimension of said array corresponding to said azimuth signal history.

19. The system as claimed in claim 15, wherein said spatial light modulator comprises a phase modulator for spatially modulating said optical beam according to said compensation phase pattern and an amplitude modulator for spatially modulating said optical beam according to said amplitude pattern of said return signal data, to produce said modulated optical beam as modulated in phase and amplitude.

20. The system as claimed in claim 15, wherein said signal comprises a radar signal.