Multifocal zone plate

• US 4,210,391 A
• Filed: 12/18/1978
• Issued: 07/01/1980
• Est. Priority Date: 09/14/1977
• Status: Expired due to Term

• Current Assignee: Allen L. Cohen
• Original Assignee: Allen L. Cohen
• Inventors: Cohen, Allen L.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Sugarman, Scott J.
• Application Number:
  US05/970,751
• Time in Patent Office: 561 Days
• Field of Search: 351/160, 351/161, 351/168, 350/211, 350/162 ZP
• US Class Current: 351/161
• 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 5/1895 such optical elements having dioptric power
• CPC Class Codes: G02C 2202/16 Laminated or compound lenses
• CPC Class Codes: G02C 2202/20 Diffractive and Fresnel lenses or lens portions

Abstract

A multifocal Fresnel lens construction suitable for use in optical systems with multifocal requirements. It is designed as a multifocal zone plate to allow an annular ring construction that isn'"'"'t width limited by diffraction aberrations. This is accomplished by modifying the phase separating annular rings of a zone plate, with curved or inclined optical facets of varying refractive indices, which can then function as Fresnel rings corresponding to the different focal powers desired.

Claims

1. A multiple focal power optical device comprising:

body means having a plurality of alternating odd and even, annular, concentric zones, bounded on the outside of radii r_n, with n=1,3,5, . . . , for the odd zones and n=2,4,6, . . . , for the even zones;

first focal power means within at least some of the odd zones for directing incident parallel light to a first focal point;

second focal power means within at least some of the even zones for directing incident parallel light to a second focal point different from said first focal point;

wherein the radii r_n of said odd and even zones are substantially proportional to square root of n.

2. The invention of claim 1 wherein said body means comprises an optically refracting material.

3. The invention of claim 2 wherein said first and second focal power means comprise a plurality of discrete refracting elements within their respective annular zones.

4. The invention of claim 3 wherein at least some of said optically refracting elements include contaminants imbedded in said body means to achieve the desired focal powers.

5. The invention of claim 4 wherein the discrete refractive elements of the first focal power means occupy every odd zone, and the discreet refractive elements of the second focal power means occupy every even zone.

6. The invention of claim 1 further including a third focal power means within at least some of the annular zones.

7. The invention of claim 1 wherein the body means is designed to act as an ophthalmic bifocal spectacle lens.

8. The invention of claim 1 wherein the body means is designed to act as an ophthalmic bifocal contact lens.

9. The invention of claim 1 wherein the said body means comprises an optically reflecting material.

10. A multiple power optical device, using the principle of interleaving annular Fresnel zones corresponding to different optical powers, wherein the radius r_n, bounding the nth Fresnel zone, is set to substantially approximate the formula r_n ≃

√

nK, where K is an arbitrary but constant length and n=1,2,3, . . . , and wherein for each specific power, all of the corresponding Fresnel zones are bounded on the outside by radii r_n, with n being either odd for all of the zones or even for all of the zones.

11. A multiple focal length optical lens, according to claim 10, wherein the Fresnel zones are refracting annular rings bounded by radii r_n, and for each n, the radius r_n is set to substantially approximate the formula r_n ≃

√

nK, where K is an arbitrary but constant length and n=1,2,3, . . . , and wherein for each specific focal length, all of the corresponding Fresnel zones are bounded by an outer radius r_n, with n being either odd for all of the zones or even for all of the zones.

12. A multiple focal length optical lens, according to claim 11, wherein only two focal lengths are used, and their corresponding Fresnel zones are presented alternately, so that every zone corresponding to one of the focal lengths is bounded on the outside by a radius r_n with n being odd, and every zone corresponding to the other focal length is bounded on the outside by a radius r_n with n being even.

13. A multiple focal length optical lens, according to claim 12, wherein it is designed to act as an ophthalmic bifocal spectacle lens.

14. A multiple focal length optical lens, according to claim 12, wherein it is designed to act as an ophthalmic bifocal contact lens.

15. A multiple power optical mirror, according to claim 10, wherein the Fresnel zones are reflecting annular rings bounded by radii r_n, and for each n, the radius r_n is set to substantially approximate the formula r_n ≃

√

nK, where K is an arbitrary but constant length and n=1,2,3, . . . , and wherein for each specific focal length, all of the corresponding Fresnel zones are bounded by an outer radius r_n, with n being either odd for all of the zones or even for all of the zones.