Article having a birefringent surface and microstructured features having a variable pitch or angles for use as a blur filter

• US 20070031140A1
• Filed: 08/04/2005
• Published: 02/08/2007
• Est. Priority Date: 08/04/2005
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Brott, Robert, Merrill, William, Black, William, Huizinga, John, Biernath, Rolf
• Granted Patent: US 7,418,202 B2
• Time in Patent Office: Days
• US Class Current: 396/268
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G02B 5/1833 comprising birefringent materials birefringent elements per se G02B5/3083
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence

Abstract

An optical low pass filter or blur filter, and method of making the filters, using an article having a birefringent surface for refracting incoming light when used with an image sensor. The birefringent surface of the article, such as a film, is structured or tilted such that, when the blur filter is placed within an optical path between a lens and the image sensor, the birefringent surface causes refraction of a light signal in the optical path into multiple light signals each being incident upon different sub-pixels within the pixels in the image sensor to prevent or reduce artifacts, such as undesirable color moiré effects, in the resulting digital image. The structures on the surface have a variable pitch or angles. The variable pitch can include a periodic, aperiodic, or quasi-aperiodic pitch, to reduce diffractive artifacts in the resulting image.

Claims

1. A blur filter, comprising:

(a) a body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) a portion of the first surface being a structured surface having a variable pitch,

wherein the portion is structured such that, when the blur filter is placed within an optical path between a lens and an image sensor, the structured surface spreads a light signal in the optical path into a plurality of light signals being at least partially spatially separated when incident upon the image sensor.

2. The blur filter of claim 1, wherein the structured surface is birefringent.

3. The blur filter of claim 1, wherein the variable pitch comprises a random pitch, an aperiodic pitch, or a quasi-aperiodic pitch.

4. The blur filter of claim 1, wherein the portion is structured such that, when placed within the optical path and used with the image sensor having pixels each having a plurality of sub-pixels, the plurality of light signals are incident upon different sub-pixels.

5. The blur filter of claim 1, wherein the blur filter causes spreading of a light signal when placed within the optical path with the third axis being substantially parallel to the optical path.

6. The blur filter of claim 1, wherein the blur filter causes spreading of a light signal when placed within the optical path with the third axis being at a non-zero angle to the optical path.

7. The blur filter of claim 1, wherein the structured surface comprises a sawtooth pattern.

8. The blur filter of claim 1, further comprising:

(a) another body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) a portion of the first surface of the other body being a structured surface having a variable pitch,

wherein the structured surface of the body includes first geometric features and the structured surface of the other body includes second geometric features, and wherein the first and second in-plane axes and the third axis of the body have a relative orientation to the first and second in-plane axes and the third axis of the other body.

9. The blur filter of claim 8, wherein the variable pitch of the other body comprises a random pitch, an aperiodic pitch, or a quasi-aperiodic pitch.

10. The blur filter of claim 8, further including a film between the body and the other body, wherein the film comprises at least one of the following:

a retarder, a wave plate, a multilayer optical film, an IR filter, or a circular polarizer.

11. The blur filter of claim 10, further including an antireflective coating on a surface of the body.

12. A blur filter, comprising:

(a) a body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) a portion of the first surface having features with variable angles,

wherein when the blur filter is placed within an optical path between a lens and an image sensor, the surface spreads a light signal in the optical path into a plurality of light signals being at least partially spatially separated when incident upon the image sensor.

13. The blur filter of claim 12, wherein the structured surface is birefringent.

14. The blur filter of claim 12, wherein the portion is structured such that, when placed within the optical path and used with the image sensor having pixels each having a plurality of sub-pixels, the plurality of light signals are incident upon different sub-pixels.

15. The blur filter of claim 12, wherein the blur filter causes spreading of a light signal when placed within the optical path with the third axis being substantially parallel to the optical path.

16. The blur filter of claim 12, wherein the blur filter causes spreading of a light signal when placed within the optical path with the third axis being at a non-zero angle to the optical path.

17. The blur filter of claim 12, wherein the structured surface comprises a sawtooth pattern.

18. The blur filter of claim 12, further comprising:

(a) another body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) a portion of the first surface of the other body having features with variable angles,

wherein the surface of the body includes first geometric features and the surface of the other body includes second geometric features, and wherein the first and second in-plane axes and the third axis of the body have a relative orientation to the first and second in-plane axes and the third axis of the other body.

19. The blur filter of claim 18, further including a film between the body and the other body, wherein the film comprises at least one of the following:

a retarder, a wave plate, a multilayer optical film, an IR filter, or a circular polarizer.

20. The blur filter of claim 19, further including an antireflective coating on a surface of the body.

21. A method of making a blur filter, comprising the steps of:

(a) providing a body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) forming a structured surface having a variable pitch on a portion of the first surface,

wherein the portion is structured such that, when the blur filter is placed within an optical path between a lens and an image sensor, the structured surface spreads a light signal in the optical path into a plurality of light signals being at least partially spatially separated when incident upon the image sensor.

22. The method of claim 21, wherein the forming step includes forming a birefringent structured surface.

23. The method of claim 21, wherein the forming step includes forming the variable pitch as a random pitch, an aperiodic pitch, or a quasi-aperiodic pitch.

24. The method of claim 21, wherein the forming step includes structuring the portion such that, when placed within the optical path and used with the image sensor having pixels each having a plurality of sub-pixels, the plurality of light signals are incident upon different sub-pixels.

25. The method of claim 21, further comprising the step of forming the structured surface such that the blur filter causes spreading of a light signal when placed within the optical path with the third axis being substantially parallel to the optical path.

26. The method of claim 21, further comprising the step of forming the structured surface such that the blur filter causes spreading of a light signal when placed within the optical path with the third axis being at a non-zero angle to the optical path.

27. The method of claim 21, wherein forming step includes forming a sawtooth pattern is the structured surface.

28. The method of claim 21, further comprising the steps of:

(a) providing another body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) forming a structured portion having a variable pitch on the first surface of the other body,

wherein the structured portion of the body includes first geometric features and the structured portion of the other body includes second geometric features, and wherein the first and second in-plane axes and the third axis of the body have a relative orientation to the first and second in-plane axes and the third axis of the other body.

29. The method of claim 28, further including providing a film between the body and the other body, wherein the film comprises at least one of the following:

a retarder, a wave plate, a multilayer optical film, an IR filter, or a circular polarizer.

30. The method of claim 28, further including forming an antireflective coating on a surface of the body.

31. An optical package having a blur filter, comprising:

a housing having a first end with an aperture, a second end with an aperture, and an interior portion that defines an optical path;

a lens within the first end wherein, when the package is placed over an image sensor with the aperture in the second end positioned adjacent the image sensor, the lens focuses incoming light onto the image sensor; and

a blur filter positioned in the optical path of the interior portion between the first and second ends of the housing, the blur filter comprising;

(a) a body having (i) first and second surfaces, and (ii) first and second in-plane axes that are orthogonal with respect to each other and a third axis that is mutually orthogonal to the first and second in-plane axes in a thickness direction of the body; and

(b) a portion of the first surface being a structured surface having a variable pitch comprising a random pitch, an aperiodic pitch, or a quasi-aperiodic pitch,

wherein the portion is structured such that, when the package is placed over the image sensor for the lens to focus the incoming light onto the image sensor, the structured surface spreads a light signal in the optical path into a plurality of light signals being at least partially spatially separated when incident upon the image sensor.