Dispersion-compensated fresnel lens

• US 5,161,057 A
• Filed: 06/13/1990
• Issued: 11/03/1992
• Est. Priority Date: 09/12/1988
• Status: Expired due to Fees

• Current Assignee: Kenneth C. Johnson
• Original Assignee: Kenneth C. Johnson
• Inventors: Johnson, Kenneth C.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): SHAFER, RICKY D
• Application Number:
  US07/537,230
• Time in Patent Office: 874 Days
• Field of Search: 350/162.16, 350/162.17, 350/162.2, 350/162.21, 350/162.22, 350/452, 350/128, 350/129, 350/167, 350/168, 126/438, 126/440, 359/565, 359/566, 359/569, 359/571, 359/572, 359/742
• US Class Current: 359/566
• CPC Class Codes: F24S 23/31 having discontinuous faces, e.g. Fresnel lenses
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration
• CPC Class Codes: G02B 27/0037 with diffracting elements G02B27/0056 takes precedence; holographic optical elements G02B5/32; zone systems G02B5/1876
• CPC Class Codes: G02B 27/4211 correcting chromatic aberrations G02B27/0056, G02B27/4222, G02B27/4227 take precedence
• CPC Class Codes: G02B 3/08 with discontinuous faces, e.g. Fresnel lens diffractive Fresnel lenses G02B5/1876
• CPC Class Codes: G02B 5/18 Diffraction gratings holographic optical elements G02B5/32, G03H; integrally combined with optical fibres G02B6/02057; for coupling light guides G02B6/34; integrally combined with optical integrated light guides G02B6/12; grating systems G02B27/44
• 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

Abstract

A transmission grating is used to reduce chromatic aberration in a Fresnel lens, wherein the lens chromatic dispersion is offset and substantially canceled by the grating'"'"'s diffraction-induced dispersion. The grating comprises a Fresnel-type pattern of microscopic facets molded directly into the lens surface. The facets would typically have a profile height of around 4·10^-5 inch and a profile width of at least 10^-3 inch. In its primary intended application, the invention would function to improve the optical performance of a Fresnel lens used to concentrate direct sunlight.

Claims

1. A dispersion-compensated Fresnel lens which accepts a polychromatic, dispersionless input beam having a specific wavefront form and transforms it into a polychromatic output beam substantially of a specific desired wavefront form with minimal dispersion, wherein:

at least one side of the lens comprises large-scale Fresnel lens facets which affect the form of the output beam through the effects of refraction;

at least a portion of one side of the lens comprises a plurality of dispersion-compensating gratings that function to mitigate the lens'"'"'s chromatic dispersion;

each of said gratings is formed as a surface relief pattern comprising small-scale grating facets superimposed on a respective one of said large-scale lens facets, wherein the grating surface affects the form of the output beam through the combined effects of refraction and diffraction;

each of said gratings has a substrate shape and facet zone structure configured so that the lens exhibits significantly less dispersion than it would without the gratings; and

each of said gratings has a Fresnel-type blazed facet structure which optimizes its first-order diffraction efficiency over a desired spectrum.

2. The dispersion compensated Fresnel lens of claim 1 wherein said plurality of dispersion-compensating gratings is confined to a peripheral portion of the lens.