Fresnel Field Lens

Abstract

Provided is a Fresnel lens for use with an array of semiconductor pixels that are separated by inactive areas, comprising a faceted surface with a plurality of facets for receiving an imaging beam, the facets being arranged into a plurality of zones separated by zone edges, and wherein the zone edges are generally aligned with the inactive areas throughout the array. Also provided are an optical detector and an imaging system incorporating such a Fresnel lens system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a non-telecentric imaging system.

FIG. 2 is a schematic drawing of a portion of the non-telecentric imaging system of FIG. 1.

FIG. 3 is a schematic drawing of a telecentric imaging system, with a generic field lens.

FIG. 4 is a schematic drawing of a telecentric imaging system, with a plano-convex field lens.

FIG. 5 is a schematic drawing of a telecentric imaging system, with a Fresnel field lens.

FIG. 6 is a schematic drawing of a telecentric imaging system, with a binary Fresnel field lens.

FIG. 7 is a schematic drawing of the zone edges of a circularly symmetric Fresnel field lens, with respect to the location of the inactive areas of an array of pixels.

FIG. 8 is a schematic drawing of the zone edges of a Fresnel field lens with concentric rectangular zones, with respect to the location of the inactive areas of an array of pixels.

FIG. 9 is a schematic drawing of the zone edges of a Fresnel field lens with zones arranged as stepwise approximations of circles, with respect to the location of the inactive areas of an array of pixels.

FIG. 10 is a plan drawing of a binary field lens.

FIG. 11 is a plan drawing of a binary field lens containing microlenses.

Claims

1. A Fresnel lens for use with an array of semiconductor pixels wherein the pixels are separated by inactive areas, comprising: a faceted surface comprising a plurality of facets for receiving an imaging beam, the facets being arranged into a plurality of zones separated by zone edges;wherein the zone edges are generally aligned with the inactive areas.

2. The Fresnel lens of claim 1, wherein the imaging beam is formed by an imaging system having an exit pupil; andwherein the Fresnel lens has a focal length roughly equal to the separation between the lens and the exit pupil.

3. The Fresnel lens of claim 1, wherein the imaging beam forms an image; and wherein the Fresnel lens is located roughly at the image.

4. The Fresnel lens of claim 1, wherein the Fresnel lens is located in close proximity to the array of semiconductor pixels.

5. The Fresnel lens of claim 1, wherein the plurality of facets is a stepwise approximation of a generalized asphere.

6. The Fresnel lens of claim 5, wherein the plurality of facets is a stepwise approximation of a spherical surface.

7. The Fresnel lens of claim 1, wherein the zone edges are arranged as concentric rectangular regions or concentric squares.

8. The Fresnel lens of claim 1, wherein the zone edges are arranged as concentric, laterally stepwise approximations of circles.

9. The Fresnel lens of claim 1, further comprising a plurality of microlenses disposed on the faceted surface within a portion of at least one of the zones.

10. The Fresnel lens of claim 9, wherein the microlenses in at least a portion of at least one zone are arranged with one lens per pixel.

11. The Fresnel lens of claim 10, wherein one of the zones is centrally located; and wherein the microlenses are further disposed within the centrally located zone.

12. An optical detector, comprising: a pixelated sensor comprising a plurality of pixels separated by inactive areas; anda Fresnel lens being disposed in proximity to the pixelated sensor for receiving an imaging beam, the Fresnel lens having a faceted surface comprising a plurality of facets, the facets being arranged into a plurality of zones separated by zone edges;wherein the zone edges are generally aligned with the inactive areas throughout the array.

13. The optical detector of claim 12, wherein the Fresnel lens has a second surface opposite the faceted surface, the second surface facing toward the pixelated sensor, and the faceted surface facing away from the pixelated sensor.

14. The optical detector of claim 13, wherein the second surface is essentially planar.

15. The optical detector of claim 12, wherein the Fresnel lens is mounted directly to the pixelated sensor.

16. The optical detector of claim 12, wherein the Fresnel lens is spaced away from the pixelated sensor.

17. An imaging system having an exit pupil, comprising: an array of semiconductor pixels; anda Fresnel lens disposed between the exit pupil and the array of semiconductor pixels, for bending an off-axis light ray emerging from the center of the exit pupil to strike the array of semiconductor pixels at near normal incidence.

18. The imaging system of claim 17, wherein the Fresnel lens is in close proximity to the array of semiconductor pixels.

19. The imaging system of claim 18, wherein the Fresnel lens has a focal length roughly equal to the separation between the exit pupil and the Fresnel lens.

20. The imaging system of claim 17, wherein the array of semiconductor pixels includes inactive areas that separate the pixels;wherein the Fresnel lens includes a plurality of zones separated by zone edges; andwherein the zone edges are generally aligned with the inactive areas.

21. The imaging system of claim 20, wherein the zones are substantially concentric and include a central zone.

22. The imaging system of claim 21, wherein the central zone includes a plurality of microlenses; and wherein one or more of the microlenses is arranged with one lens per pixel.

23. The imaging system of claim 22, wherein each of the pixels respectively comprises an active portion and an inactive portion; and wherein the microlenses are arranged with one lens disposed over each pixel for directing light onto the active portions.

24. The imaging system of claim 17, wherein the array of semiconductor pixels has a periodicity; and wherein the zone edges are arranged to match the periodicity of the array of semiconductor pixels.

25. The imaging system of claim 24, wherein the periodicity of the array of semiconductor pixels is rectangular; and wherein the zone edges are rectangular.