Optical method and system for extended depth of focus

• US 7,365,917 B2
• Filed: 02/16/2007
• Issued: 04/29/2008
• Est. Priority Date: 08/16/2004
• Status: Active Grant

• Current Assignee: Brien Holden Vision Institute
• Original Assignee: Xceed Imaging Ltd.
• Inventors: Zalevsky, Zeev
• Primary Examiner(s): THOMPSON, TIMOTHY J
• Application Number:
  US11/707,271
• Publication Number:
  US 20070236769A1
• Time in Patent Office: 438 Days
• Field of Search: 359/738, 359/739, 359/559, 359/558, 359/721, 359/740, 438/468, 438/535, 438/508
• US Class Current: 359/738
• CPC Class Codes: A61F 2/16 Intraocular lenses
• CPC Class Codes: A61F 2/1613 having special lens configurations, e.g. multipart lenses; having particular optical properties, e.g. pseudo-accommodative lenses, lenses having aberration corrections, diffractive lenses, lenses for variably absorbing electromagnetic radiation, lenses having variable focus
• CPC Class Codes: A61F 2/1648 Multipart lenses
• CPC Class Codes: A61F 2250/0053 differing in optical properties
• CPC Class Codes: G02B 2207/129 Coded aperture imaging
• CPC Class Codes: G02B 27/0075 with means for altering, e.g. increasing, the depth of field or depth of focus
• CPC Class Codes: G02B 27/58 Optics for apodization or superresolution; Optical synthetic aperture systems
• CPC Class Codes: G02C 2202/16 Laminated or compound lenses
• CPC Class Codes: G02C 2202/22 Correction of higher order and chromatic aberrations, wave front measurement and calculation
• CPC Class Codes: G02C 7/02 Lenses; Lens systems ; Methods of designing lenses

Abstract

An imaging arrangement and method for extended the depth of focus are provided. The imaging arrangement comprises an imaging lens having a certain affective aperture, and an optical element associated with said imaging lens. The optical element is configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition. The optical element and the imaging lens define a predetermined pattern formed by spaced-apart substantially optically transparent features of different optical properties. Position of at least one phase transition region of the optical element within the imaging lens plane is determined by at least a dimension of said affective aperture.

Claims

1. An imaging arrangement comprising:

an imaging lens assembly including at least one lens having a certain affective aperture, and at least one optical element associated with said at least one lens and configured to provide an extended depth of focus of the imaging arrangement, said optical element being configured as a phase-affecting, non-diffractive optical element defining a spatially low frequency phase transition, said optical element together with its associated lens defining a predetermined pattern formed by spaced-apart optically transparent features of different optical properties, position of at least one phase transition region of the optical element within the lens plane being determined by at least a dimension of said affective aperture.

2. The arrangement of claim 1, wherein said lens assembly includes the single lens associated with the single optical element.

3. The arrangement of claim 1, comprising the lens assembly including an array of lenses, and an array of the optical elements, each optical element being associated with the corresponding one of the lenses.

4. The arrangement of claim 1, wherein said optical element is configured as a phase-only element.

5. The arrangement of claim 4, wherein said optical element is configured as a binary mask.

6. The arrangement of claim 1, wherein said optical element is a configured as a phase and amplitude affecting element.

7. The arrangement of claim 1, wherein the optical element is configured to maximize a defocused optical transfer function (OTF) of the imaging arrangement by providing the out of focus OTF as much as possible away from zero.

8. The arrangement of claim 7, wherein the optical element is configured to produce proper phase interference relation between light portions passing through different regions of the imaging arrangement corresponding to the different features of the pattern to thereby reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens.

9. The arrangement of claim 1, wherein said at least one transition region is configured as a pi-phase transition for a certain wavelength for which the optical element is designed.

10. The arrangement of claim 1, wherein said at least one transition region is configured as about pi/2 phase transition for a certain wavelength range for which the optical element is designed.

11. The arrangement of claim 1, wherein the position of said at least one transition region with respect to the imaging lens is determined by optical power of the imaging lens.

12. The arrangement of claim 7, wherein the position for N transition regions of the optical element within the imaging lens plane maximizing the OTF is determined as:

$\underset{a_n}{\max }<br><br>\left\{\min <br><br>\left\{\left[\stackrel{\sim <br><br>}{D}<br><br>\left(v\right)<br><br>\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>a_n<br><br>\mathrm{rect}<br><br>\left(\frac{v-n<br><br><br><br>\mathrm{\Delta <br><br>}<br><br><br><br>v}{\mathrm{\Delta <br><br>}<br><br><br><br>v}\right)\right]\otimes <br><br>\left[\stackrel{\sim <br><br>}{D}<br><br>\left(v\right)<br><br>\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>a_n<br><br>\mathrm{rect}<br><br>\left(\frac{v-n<br><br><br><br>\mathrm{\Delta <br><br>}<br><br><br><br>v}{\mathrm{\Delta <br><br>}<br><br><br><br>v}\right)\right]\right\}\right\}$

values for a_n providing maximum for minima of an expression for auto correlation of a Coherent Transfer Function (CTF) of the imaging lens, where a_n equals either 1 or −

1, {tilde over (D)}(v) being the CTF of the imaging lens corresponding to out of focus position of an object being imaged and being determined as

$\stackrel{\sim <br><br>}{D}<br><br>\left(v\right)=\exp <br><br>\left(\frac{\mathrm{i<br><br>}<br><br><br><br>4<br><br>\mathrm{\Psi <br><br>}<br><br><br><br>v^{2<br><br>}}{D^2}\right),$

wherein D is the affective aperture dimension, v is a coordinate of the affective aperture in the CTF plane, and ψ

is a phase factor representing a degree of getting out of focus.

13. The arrangement of claim 1, wherein said at least one transition region has a sub-pattern formed by an array of variable phase transition sub-regions.

14. The arrangement of claim 9, wherein said at least one pi-phase transition region has a sub-pattern formed by an array of variable pi-phase transition sub-regions.

15. The arrangement of claim 1, wherein the optical element is configured as at least one annular transition region.

16. The arrangement of claim 1, wherein the optical element is configured as a grid.

17. The arrangement of claim 1, wherein said optical element is spaced-apart from the imaging lens along an optical axis of the imaging lens.

18. The arrangement of claim 1, wherein said optical element is attached to the imaging lens.

19. The arrangement of claim 1, wherein said optical element is made integral with the imaging lens.

20. The arrangement of claim 1, wherein said optical element is configured as a mask formed by an array of said transition regions arranged in a spaced-apart relationship being spaced by the optically transparent regions of the imaging lens within the imaging lens plane.

21. The arrangement of claim 1, comprising two phase affecting optical elements located in spaced-apart substantially parallel planes at opposite sides, respectively, of said at least one lens.

22. The arrangement of claim 19, wherein said at least one transition region is formed as a surface relief on the imaging lens surface, defining a lens thickness within said at least one region different from that within other regions of the lens.

23. The arrangement of claim 19, wherein said at least one transition region is formed by a material having refractive index different from that of the imaging lens material.

24. The arrangement of claim 19, wherein said optical element is configured as a mask formed by an array of the phase transition regions formed by a material having refractive index different from that of the imaging lens material.

25. The arrangement of claim 7, wherein the optical element is configured to maximize the OTF by reducing high-frequency cancellation at large shifts of a Coherent Transfer Function (CTF) of the imaging lens.

26. The arrangement of claim 7, wherein the optical element is configured to maximize the OTF by reducing sensitivity of the lens arrangement to shifts of a Coherent Transfer Function (CTF) of the imaging lens while getting out of focus.

27. The arrangement of claim 1, wherein the optical element is configured to produce periodic replication of a lateral phase shape of a light field propagating through the imaging lens.

28. The arrangement of claim 1, wherein the optical element is configured in accordance with a free space propagation of the optical element function for a distance between the optical element and the imaging lens plane.

29. The arrangement of claim 1, wherein the optical element is configured to produce non-periodic replication of a lateral phase shape of a light field propagating through the imaging lens.

30. The arrangement of claim 1, wherein the optical element is configured to produce random replication of a lateral phase shape of a light field propagating through the imaging lens.

31. The arrangement of claim 1, for use in patients'"'"' spectacles.

32. An optical element for use with an imaging lens in the imaging arrangement of claim 1 for extending depth of focus of imaging, the optical element being configured as a phase-affecting, non-diffractive optical element defining a predetermined pattern of spatially low frequency phase transitions, said pattern being defined by an affective aperture of the given imaging lens.

33. A system for creating an image of an object on a detector plane, the system comprising the imaging lens arrangement of claim 1.

34. The system of claim 32, wherein said object is a screen of a display device to be imaged on the eye retina constituting the detector plane.

35. A display device carrying the imaging arrangement of claim 1.

37. A method for designing the optical element of claim 32, said designing comprising selecting N positions for the phase transitions within the imaging lens effective aperture as those providing maximal contrast of an Optical Transfer Function (OTF) of the imaging system under a set of out of focus locations, thereby providing the out of focus OTF as much as possible away from zero.

38. The method of claim 37, wherein the positions for said N transition regions of the optical element within the imaging lens plane maximizing the OTF are determined as:

$\underset{a_n}{\max }<br><br>\left\{\min <br><br>\left\{\left[\stackrel{\sim <br><br>}{D}<br><br>\left(v\right)<br><br>\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>a_n<br><br>\mathrm{rect}<br><br>\left(\frac{v-n<br><br><br><br>\mathrm{\Delta <br><br>}<br><br><br><br>v}{\mathrm{\Delta <br><br>}<br><br><br><br>v}\right)\right]\otimes <br><br>\left[\stackrel{\sim <br><br>}{D}<br><br>\left(v\right)<br><br>\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br><br><br>a_n<br><br>\mathrm{rect}<br><br>\left(\frac{v-n<br><br><br><br>\mathrm{\Delta <br><br>}<br><br><br><br>v}{\mathrm{\Delta <br><br>}<br><br><br><br>v}\right)\right]\right\}\right\}$

values for a_n providing maximum for minima of an expression for auto correlation of a Coherent Transfer Function (CTF) of the imaging lens, where a_n equals either 1 or −

1, {tilde over (D)}(v) being the CTF of the imaging lens corresponding to out of focus position of an object being imaged and being determined as

$\stackrel{\sim <br><br>}{D}<br><br>\left(v\right)=\exp <br><br>\left(\frac{\mathrm{i<br><br>}<br><br><br><br>4<br><br>\mathrm{\Psi <br><br>}<br><br><br><br>v^{2<br><br>}}{D^2}\right),$

wherein D is the affective aperture dimension, v is a coordinate of the affective aperture in the CTF plane, and, and ψ

is a phase factor representing a degree of getting out of focus.

39. The method of claim 37, comprising fabricating a mask formed by an arrangement of the N transitions spaced-apart from each other in accordance with said selected N positions.

40. The method of claim 39, comprising attaching said mask to the surface of the imaging lens aperture.

41. The method of claim 37, comprising patterning the surface of the imaging lens aperture to form a mask of the N transitions spaced-apart from each other in accordance with said selected N positions.

42. The method of claim 40, comprising providing said surface substantially flat to thereby allow insertion of the patterned imaging lens into a patient'"'"'s eye.

43. The method of claim 37, wherein the designing of the optical element comprises producing a phase interference relation between light portions passing through said N regions and spaces between them to thereby reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of an arrangement formed by the imaging lens and the optical element.

44. The method of claim 41, wherein said patterning comprises applying material removal to the lens regions within said N positions, and filling said regions, from which the lens material has been removed, by a material of a refraction index different from that of the lens, so as to provide a refraction index difference such that the outer region of the patterned lens is flat and proper equalization between the different material regions is provided to produce a phase interference relation between light portions passing through different material regions to thereby reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of the patterned imaging lens.

45. The method of claim 41, wherein said patterning comprises applying diffusion or photo polymerization to the lens regions within said N positions, so as to provide a refraction index difference between said N regions and spaces between them such that the outer region of the patterned lens is flat and proper equalization between the different material regions is provided to produce a phase interference relation between light portions passing through different material regions to thereby reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of the patterned imaging lens.

46. The method of claim 37, comprising implanting in the patient'"'"'s eye tissue, within said selected N positions, an artificial tissue having a refraction index different from that of the eye tissue.

36. A method for providing a certain extended depth of focus of an imaging system, the method comprising applying an aperture coding to an imaging lens having a certain effective aperture, by applying to the imaging lens at least one phase-affecting non-diffractive optical element configured to define a spatially low frequency phase transition arrangement and thereby provide a predetermined pattern of spaced-apart substantially optically transparent features of different optical properties within the imaging lens plane, thereby producing phase interference relation between light portions passing through different regions of the lens arrangement corresponding to the different features of the pattern so as to reduce a quadratic phase factor resulting from light getting out of focus of the imaging lens and maximize a defocused optical transfer function (OTF) of the imaging lens arrangement.