Diffractive/Refractive lenslet array incorporating a second aspheric surface

• US 5,751,492 A
• Filed: 06/14/1996
• Issued: 05/12/1998
• Est. Priority Date: 06/14/1996
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Meyers, Mark Marshall
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): MACK, RICKY LEVERN
• Application Number:
  US08/663,887
• Time in Patent Office: 697 Days
• Field of Search: 359/619, 359/621, 359/622, 359/623, 359/626, 359/625
• US Class Current: 359/619
• CPC Class Codes: G02B 3/0043 Inhomogeneous or irregular arrays, e.g. varying shape, size, height
• CPC Class Codes: G02B 3/0056 arranged along two different directions in a plane, e.g. honeycomb arrangement of lenses G02B3/0043 takes precedence; miniaturised objectives for electronic devices employing wafer level optics G02B13/0085
• CPC Class Codes: G02B 3/04 with continuous faces that are rotationally symmetrical but deviate from a true sphere , e.g. so called "aspheric" lenses
• CPC Class Codes: G02B 5/1876 Diffractive Fresnel lenses; Zone plates; Kinoforms G02B5/1842, G02B5/1847 take precedence; optical systems having diffractive correction means G02B27/0037; Fresnel lenses operating by refraction G02B3/08
• CPC Class Codes: G02B 5/1885 Arranged as a periodic array
• CPC Class Codes: G02B 5/1895 such optical elements having dioptric power

Abstract

A short focal length image sensor comprising:

a color photosensor array comprised of sets of three photosensors with red, green, and blue, filters positioned over respective photosensors in each set;

a lenslet array corresponding in the number of lenslets to the number of sets of photosensors in said color photosensor array, wherein each lenslet is formed with a first convex, spherical surface having diffractive means incorporated thereon and a second surface which is aspheric, substantially opposite said first surface with the size of said lenslet array being greater than the size of said photosensor array by an amount that allows the local optical axis of each lenslet at the largest field angle to image incident light onto the set of photosensors associated with the image sensors largest field angle; and

an array of aperture stops combined with an array of field stops wherein the number of field and aperture stops corresponds to the number of lenslets and wherein each field and aperture stop is aligned to the center of the local optical axis for an associated set of photosensors.

Claims

1. An image sensor comprising:

a color photosensor array comprised of a number of sets of three photosensors with red, green, and blue, filters positioned over respective photosensors in each set;

a lenslet array having a number of lenslets equal to the number of three sets of photosensors in said color photosensor array, wherein each lenslet is formed with a first convex, spherical surface having diffractive means incorporated thereon and a second surface which is aspheric and opposite said first surface with the size of said lenslet array being greater than the size of said color photosensor array by an amount that allows the mechanical optical axis of each lenslet, at the largest field angle, to image incident light onto a set of three photosensors; and

an array of aperture stops combined with an array of field stops wherein the number of field stops and the number of aperture stops are equal to the number of lenslets and wherein each field and aperture stop is aligned to the center of the mechanical optical axis of a lenslet.

2. The image sensor according to claim 1 wherein the second surface of each lenslet is an aspheric surface that is convex at the lenses physical center and transitions to a concave surface towards the edge of the lens.

3. The image sensor according to claim 1 wherein said array of aperture stops is positioned in front of said lenslet array.

4. The image sensor according to claim 1 wherein said array of aperture stops is positioned between said lenslet array and said color photosensor array.

5. The image sensor according to claim 1 wherein the lenslets of said array of lenslets are abutting.

6. The image sensor according to claim 1 wherein each lenslet is positioned in said array so as to view a different fraction of the total field of view of the image sensor.

7. The image sensor according to claim 1 and further comprising a plurality of baffles extending between each lenslet and a set of three photosensors for preventing stray light from an adjacent lenslet impinging on a neighboring set of three photosensors.