Extended depth of field optical systems

• US 7,583,442 B2
• Filed: 05/14/2007
• Issued: 09/01/2009
• Est. Priority Date: 02/03/1995
• Status: Expired due to Term

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Original Assignee: OmniVision CDM Optics, Inc.
• Inventors: Dowski, Edward R. Jr., Cathey, Wade Thomas Jr.
• Primary Examiner(s): Chang; Audrey Y
• Application Number:
  US11/748,326
• Publication Number:
  US 20080174869A1
• Time in Patent Office: 841 Days
• Field of Search: 359/558
• US Class Current: 359/558
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 3/7835 using coding masks
• CPC Class Codes: G02B 21/14 affording illumination for phase-contrast observation
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G02B 27/52 Phase contrast optics in microscopes G02B21/14
• CPC Class Codes: G02B 5/00 Optical elements other than lenses light guides G02B6/00; optical logic elements G02F3/00
• CPC Class Codes: G02B 7/365 by analysis of the spatial frequency components of the image
• CPC Class Codes: G02B 7/40 using time delay of the reflected waves, e.g. of ultrasonic waves

Abstract

An imaging system is characterized at least by an ambiguity function (“AF”) and a point spread function (“PSF”). The AF is a function of parameters u and v related to a misfocus parameter ψ; the PSF is at least a function of ψ. The system includes (1) an image recording device, (2) an optical arrangement for imaging an object to the image recording device, and (3) a post processor that renders an in-focus electronic image over a range of distances between the object and the optical arrangement. The optical arrangement alters phase such that a main lobe of the AF is broader in v for a specific u. The PSF has a functionally different form for a specific ψ, in comparison to a PSF characterizing the system when the optical arrangement does not alter the phase for those specific values of u and ψ over the range of distances.

Claims

1. An imaging system characterized at least by an ambiguity function and a point spread function (PSF), which ambiguity function is a function of a normalized spatial frequency parameter u and a vertical variable v related to a misfocus parameter ψ

, and which PSF is at least a function of the misfocus parameter ψ

, the imaging system comprising;

an image recording device for converting light imaged thereon into a stored image;

an optical arrangement for imaging light from an object to the image recording device to generate the stored image, which light is characterized by at least phase; and

a post processor for processing the stored image from the image recording device, in accordance with the PSF, to render an in-focus electronic image over a range of object distances between the object and the optical arrangement,

wherein the optical arrangement is configured for altering the phase such that a main lobe of the ambiguity function is broader in v for a given value of u over an optical bandpass of the imaging system, and the PSF has a functionally different form for a given value of ψ

, in comparison to a main lobe of an ambiguity function, a PSF and the optical bandpass, respectively, characterizing the imaging system when the optical arrangement does not alter the phase for those given values of u and ψ

over the range of object distances.

2. An imaging system of claim 1, the image recording device comprising a charge-coupled device (CCD).

3. An imaging system of claim 1, wherein the optical arrangement is formed of an optical material selected from glass and plastic.

4. An imaging system of claim 3, the optical arrangement having variations in at least a selected one of opaqueness, thickness, diffractive properties and index of refraction to alter the phase of the light.

5. An imaging system of claim 1, the optical arrangement implementing a cubic phase modulation.

6. An imaging system of claim 1,the post processor comprising a digital signal processing algorithm.

7. An imaging system of claim 1, the post processor comprising an electronic chip.

8. An imaging system of claim 1, the post processor implementing a function

$\sqrt{\frac{3}{}}$



α

⁢

⁢

u 

π

⁢

ⅇ

j ⁢

⁢

α

⁢

⁢

u 3 4 ,

where α

is a parameter used to adjust the range of object distances and u is a normalized, unitless spatial frequency parameter, to remove an imaging effect induced by the optical arrangement.

9. An imaging system of claim 1, the light further including amplitude, and wherein the optical arrangement includes variations in at least a selected one of opaqueness, thickness and index of refraction so as to affect both of the phase and the amplitude.

10. An imaging system of claim 1, the optical arrangement altering the phase at two different locations in the imaging system.

11. A method for decreasing optical sensitivity to misfocus-related aberrations in an optical system characterized at least by an ambiguity function and a point spread function (PSF), which ambiguity function is a function of a normalized spatial frequency parameter u and a vertical variable v related to a misfocus parameter ψ

, and which PSF is at least a function of the misfocus parameter ψ

, the method comprising the steps of;

imaging light from an object to form an optical image, which light is characterized by at least phase;

detecting the optical image to generate a stored image; and

post processing the stored image, in accordance with the PSF, to render an in-focus electronic image over a range of object distances between the object and the imaging system,

wherein imaging includes altering at least phase of the light such that a main lobe of the ambiguity function is broader in v for a given value of u over an optical bandpass of the optical system, and the PSF has a functionally different form for a given value of ψ

, in comparison to a main lobe of an ambiguity function, a PSF and the optical bandpass, respectively, characterizing the optical system without altering the phase for those given values of u and ψ

, over the range of object distances.

12. The method of claim 11, wherein altering the phase includes altering the phase at two different locations in the optical system.

13. A method for increasing a depth of field of an optical system characterized at least by an ambiguity function and a point spread function (PSF), which ambiguity function is a function of a normalized spatial frequency parameter u and a vertical variable v related to a misfocus parameter ψ

, and which PSF is at least a function of the misfocus parameter ψ

, the method comprising;

imaging light from an object to form an image, the light being characterized by phase and amplitude;

forming a digital representation of the image; and

electronically processing the digital representation,

wherein imaging includes altering at least the phase while maintaining the amplitude such that a main lobe of the ambiguity function is broader in v for a given value of u over an optical bandpass of the imaging system, and the PSF has a functionally different form in comparison to a main lobe of an ambiguity function, a PSF and the optical bandpass, respectively, characterizing the optical system without altering the phase for those given values of u and ψ

, over a range of object distances between the object and the optical system, and

wherein electronically processing includes modifying the digital representation in accordance with the PSF to render an in-focus electronic image over the range of object distances.

14. The method of claim 13, wherein forming the digital representation of the image includes capturing the image with a charge-coupled device (CCD) array.

15. The method of claim 13, wherein altering at least the phase comprises modulating the phase with a selected one of a linear phase modulation and a cubic phase modulation.

16. The method of claim 13, wherein altering at least the phase comprises diffracting the light.

17. The method of claim 13, further comprising storing the digital representation of the image for use in the electronically processing.

18. The method of claim 13, wherein electronically processing comprises filtering the image.

19. The method of claim 13, wherein altering the phase includes altering the phase at two different locations in the optical system.