OPTICAL ANGLE OF ARRIVAL MEASUREMENT SYSTEM AND METHOD

• US 20100230577A1
• Filed: 03/10/2009
• Published: 09/16/2010
• Est. Priority Date: 03/10/2009
• Status: Active Grant

• Current Assignee: Teledyne Scientific & Imaging, LLC (Teledyne Technologies Incorporated)
• Original Assignee: Teledyne Scientific Imaging LLC
• Inventors: MA, JIAN, Winker, Bruce K.
• Granted Patent: US 8,334,499 B2
• Time in Patent Office: Days
• US Class Current: 250/208.100
• CPC Class Codes: G01S 3/783 using amplitude comparison of signals derived from static detectors or detector systems

Abstract

An optical angle of arrival measurement system uses an optical element to form at least one narrow width line on a focal plane array (FPA) which is oblique with respect to the FPA'"'"'s row and column axes and which traverses at least two rows or columns along its length; forming two perpendicular narrow width lines in a cross-pattern is preferred. Interpolating the position of the lines on the FPA provides coordinates that can be used to calculate the optical angle of arrival in accordance with θx=A(x)·tan⁻¹(x/f), and θy=B(y)·tan⁻¹(y/f), where f is the focal length of the optical element, and A(x) and B(y) are parameters that account for optical distortion and other imperfections of the system. The resolution δθ of the angle of arrival measurement can be improved to at least δθ˜(d/n)/f, where d is the FPA pixel width and n is the length in pixels of the imaged line.

Claims

1. An optical angle of arrival measurement system, comprising:

a focal plane array (FPA) comprising an M row×

N column array of pixels, said rows and said columns being parallel to a row axis and a column axis, respectively; and

one or more optical elements arranged to converge incoming light from one or more point sources onto said FPA in a predetermined pattern of lines which are oblique with respect to the row and column axes of said FPA, such that the position of said lines on said FPA varies with the angular position of said point source(s) relative to said measurement system.

2. The system of claim 1, wherein said predetermined light pattern comprises at least one narrow width line which is oblique with respect to said row and column axes and which traverses at least two of said rows or columns along its length.

3. The system of claim 2, wherein said predetermined light pattern comprises two perpendicular narrow width lines that form a cross-pattern, each of said lines being oblique with respect to said row and column axes and traversing at least two of said rows or columns along their respective lengths.

4. The system of claim 2, wherein said system is arranged such that each of said narrow width oblique lines traverses three of said rows or columns along their respective lengths.

5. The system of claim 2, wherein said narrow width oblique lines have a width equal or approximately equal to the FPA pixel width.

6. The system of claim 2, further comprising a means for interpolating the positions of said narrow width lines on said FPA.

7. The system of claim 5, wherein said means for interpolating the positions of said narrow width lines on said FPA provides x and y coordinates which represent the angle of arrival of said incoming light, said angle of arrival given by θ

_x, θ

_y, where θ

x=A(x)·

tan<sup>−

1</sup>(x/f), and θ

y=B(y)·

tan<sup>−

1</sup>(y/f), where f is the focal length of said optical element, and A(x) and B(y) are parameters that account for optical distortion and other imperfections of the system.

8. The system of claim 5, wherein said means for interpolating the positions of said narrow width lines on said FPA comprises employing a peak search algorithm.

9. The system of claim 5, wherein said means for interpolating the positions of said narrow width lines on said FPA comprises determining the optical intensity distribution of the light converged on said FPA.

10. The system of claim 5, wherein said means for interpolating the positions of said narrow width lines on said FPA comprises fitting respective linear functions to the patterns of pixels illuminated by said lines.

11. The system of claim 5, wherein said means for interpolating the positions of said narrow width lines on said FPA comprises fitting respective nonlinear functions to the patterns of pixels illuminated by said lines.

12. The system of claim 11, wherein said nonlinear functions comprise second-order polynomials.

13. The system of claim 2, wherein said pixels have a width d, said optical element has a focal length f, and said at least one narrow width oblique line is n pixels in length, said measurement system arranged such that its resolution δ

θ

is proportional to (d/n)/f.

14. The system of claim 1, wherein said optical element comprises a diffractive optical element (DOE).

15. The system of claim 14, further comprising one or more lenses between said DOE and said FPA.

16. The system of claim 1, wherein said optical element comprises first and second orthogonal birefringent cylindrical lens assemblies, said first birefringent cylindrical lens assembly having a focusing power in the x-direction for the x-polarization component of the light only and said second birefringent cylindrical lens assembly having a focusing power in the y-direction for y-polarization component of the light only, said lenses arranged such that incoming light converges onto said FPA as two perpendicular narrow width lines, each of which is oblique with respect to said row and column axes and traverses at least two of said rows or columns along its length.

17. The system of claim 16, wherein each of said narrow width oblique lines has a width equal or approximately equal to the FPA pixel width.

18. The system of claim 1, wherein said optical element comprises a first non-birefringent cylindrical lens rotated with respect to said row and column axes such that incoming light converges on said FPA as a narrow width line which is oblique with respect to said row or column axes and which traverses at least two of said second FPA'"'"'s rows or columns along its length.

19. The system of claim 18, further comprising:

a second non-birefringent cylindrical lens which is orthogonally oriented with respect to said first non-birefringent cylindrical lens; and

a second FPA comprising a row and column array of pixels, said rows and columns being parallel to a row axis and a column axis, respectively;

said second non-birefringent cylindrical lens converging incoming light onto said second FPA as a narrow width line which is oblique with respect to the row and column axes of said second FPA and which traverses at least two of said second FPA'"'"'s rows or columns along its length.

20. The system of claim 19, wherein each of said narrow width oblique lines has a width equal or approximately equal to the FPA pixel width.

21. The system of claim 19, further comprising a means for interpolating the positions of said lines on said first and second FPAs.

22. The system of claim 1, wherein said incoming light is produced by a laser, light-emitting diode, or star.

23. The system of claim 1, wherein said optical elements are arranged to detect incoming light over a limited range of wavelengths.

24. The system of claim 1, further comprising an optical bandpass filter installed in front of said optical elements so as to limit the range of wavelengths reaching said optical elements.

25. The system of claim 24, wherein said optical bandpass filter is a narrow bandpass, high out-of-band rejection, large FOV optical filter.

26. The system of claim 1, wherein said optical element comprises two or more optical components.

27. The system of claim 1, wherein said FPA is employed within the body of a camera.

28. The system of claim 27, wherein said camera includes two of said FPAs, said camera comprising a single optical aperture and arranged to image the orthogonal lines produced by said optical element on respective ones of said FPAs.

29. The system of claim 28, wherein said camera includes two of said FPAs, said camera comprising a single optical aperture and arranged to image the orthogonal lines produced by said optical element onto different regions of a single FPA.