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

• US 7,418,202 B2
• Filed: 08/04/2005
• Issued: 08/26/2008
• Est. Priority Date: 08/04/2005
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Brott, Robert L., Huizinga, John S., Merrill, William Ward, Black, William B., Biernath, Rolf W.
• Primary Examiner(s): KOVAL, MELISSA J
• Application Number:
  US11/196,887
• Publication Number:
  US 20070031140A1
• Time in Patent Office: 1,118 Days
• Field of Search: 396/268, 396/101, 396/209, 396/241, 396/275, 396/307, 348/335, 348/256, 348/224.1, 348/270, 348/273, 348/290, 348/342, 348/360, 359/486, 359/501, 359/575, 359/576, 359494-497, 359/569
• 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 and a linear geometric feature,

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, and

wherein the body has birefringence and the birefringence is imparted by stretching the body after forming the linear geometric feature on the body, and wherein a cross sectional shape of the linear geometric feature after the stretching is substantially identical to a cross sectional shape of the linear geometric feature prior to the stretching.

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

3. 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.

4. 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.

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 at a non-zero angle to the optical path.

6. The blur filter of claim 1, further including a film positioned adjacent the 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.

7. The blur filter of claim 6, further including an antireflective coating on a surface of the body.

8. 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 geometric 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, and

wherein the body has birefringence and the birefringence is imparted by stretching the body after forming the geometric features on the body, and wherein a cross sectional shape of the geometric features after the stretching are substantially identical to a cross sectional shape of the geometric features prior to the stretching.

9. The blur filter of claim 8, 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.

10. The blur filter of claim 8, 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.

11. The blur filter of claim 8, 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.

12. The blur filter of claim 8, further including a film positioned adjacent the 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.

13. The blur filter of claim 12, further including an antireflective coating on a surface of the body.

14. 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 and a linear geometric feature 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, and

wherein the body has birefringence and the birefringence is imparted by stretching the body after forming the linear geometric features on the body, and wherein a cross sectional shape of the linear geometric features after the stretching is substantially identical to a cross sectional shape of the linear geometric features prior to the stretching.

15. The method of claim 14, wherein the forming step includes forming the variable pitch as a random pitch, an aperiodic pitch, or a quasi-aperiodic pitch.

16. The method of claim 14, 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.

17. The method of claim 14, 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.

18. The method of claim 14, 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.

19. 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 linear geometric feature and 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, and

wherein the body has birefringence and the birefringence is imparted by stretching the body after forming the linear geometric features on the body, and wherein a cross sectional shape of the linear geometric features after the stretching is substantially identical to a cross sectional shape of the linear geometric features prior to the stretching.