Optical element employing aspherical and binary grating optical surfaces

• US 5,044,706 A
• Filed: 02/06/1990
• Issued: 09/03/1991
• Est. Priority Date: 02/06/1990
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Chen, Chungte W.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): Lerner, Martin
• Application Number:
  US07/475,526
• Time in Patent Office: 574 Days
• Field of Search: 350/162.16, 350/452, 350/443, 350/1.2, 350/1.3, 350/1.4, 350/162.22, 350/469
• US Class Current: 359/357
• CPC Class Codes: G02B 13/14 for use with infrared or ultraviolet radiation G02B13/008, G02B13/16 take precedence
• CPC Class Codes: G02B 13/18 with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration G02B13/002 takes precedence
• 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 27/4216 correcting geometrical aberrations
• 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

An optical element (12) has aspherical (14) and binary grating (16) optical surfaces. In the preferred embodiment, the optical element (12) is a positive meniscus optical element made of germanium having a useful spectral bandpass in the infrared wavelength region. A telescope (100) includes a first positive meniscus optical element (102), having a convex aspherical surface (104) and a concave binary grating surface (106). A first negative meniscus optical element (107) having a concave binary grating surface (108) and a concave aspherical surface (110) is employed. Next is a positive power lens (112), followed by a second negative meniscus lens (118). In the preferred embodiment, the first negative meniscus optical element (107) and the positive power lens (112) are affixed to a common housing (124), which is removable from the telescope system. Removal of the housing (124) converts the telescope (100) system from a wide-field-of-view telescope (100) to a narrow-field-of-view telescope (40).

Claims

1. An optical element for reducing aberration in an optical system, said optical element having first and second surfaces, said first surface being an aspherical surface and said second surface being a diffractive surface and, wherein said second surface is a binary grating surface including a plurality of concentric rings, each ring having a series of phase level steps for approximating a Kinoform profile.

2. The optical element of claim 1, wherein said first surface is convex and said second surface is concave.

3. The optical element of claim 1, wherein said first and second surfaces are concave.

4. The optical element of claim 1 made of germanium.

5. The optical element of claim 1, being capable of correcting primary chromatic aberration, spherical and spherochromatic aberration of all orders, and third order coma and reducing lateral chromatic aberration for focal ratios as low as F/0.5.

6. The optical element of claim 1, having a useful spectral bandpass for energy in the infrared wavelength region.

7. An optical element for reducing aberration in an optical system, said optical element having first and second surfaces, said first surface being an aspherical surface and said second surface being a binary grating surface, said optical element being made of germanium and having a useful spectral bandpass for energy in the infrared wavelength region.

8. The optical element of claim 7 wherein said binary grating surface comprises:

a plurality of concentric rings, each ring having a series of phase level steps for approximating a Kinoform profile.

9. The optical element of claim 7, being capable of correcting primary chromatic aberration, spherical and spherochromatic aberration of all orders, and third order coma, and reducing lateral chromatic aberration, for focal ratios as low as F/0.5.

10. A telescope system having an optical axis comprising:

(a) a first positive meniscus optical element on said optical axis, having a first convex surface and a second concave surface, said first surface being an aspherical surface and said second surface being a binary grating surface;

(b) a first negative meniscus optical element, on said optical axis behind said first positive meniscus optical element and having first and second concave surfaces, said first surface being a binary grating surface and said second surface being an aspherical surface;

said binary grating surfaces comprising a plurality of concentric rings, each ring having a series of phase level steps for approximating a Kinoform profile;

(c) a positive power optical element, on said common optical axis behind said first negative meniscus optical element, having surfaces which are substantially spherical; and

(d) a second negative meniscus optical element, on said optical axis behind said positive power optical element.

11. The telescope of claim 10, wherein said first positive meniscus optical element, said first negative meniscus optical element, said positive power optical element, and said second negative meniscus optical element are made of germanium and have a useful spectral bandpass within the infrared wavelength region.

12. The telescope of claim 10, wherein said first positive meniscus optical element and said first negative meniscus optical element are capable of correcting primary chromatic aberration, spherical and spherochromatic aberration of all orders, and third order coma, and reducing lateral chromatic aberration for focal ratios as low as F/0.5.

13. The telescope system of claim 10, wherein the four optical elements comprise the optical elements A, B, C, and D, and are shown in FIG. 5 of the drawings as 102, 107, 112, and 118, and wherein said optical elements are fabricated and mounted in accordance with the following prescription Table 2 wherein "Radius" refers to radius of curvature of the optical element surface indicated by the corresponding number, the "Thickness" refers to the distance along the optical axis 0 from the indicated surface to the surface of next highest number, and the materials are as specified, all of the surfaces being spherical except for the first positive meniscus optical element whose first surface is aspherical and whose curvature constants c, k, d, e, f, and g are given in the Table 2, and the first negative meniscus optical element whose second surface is aspherical and whose curvature constants c, k, d, e, f, and g are given in the Table 2, and wherein the second surface of the first positive meniscus optical element and the first surface of the first negative meniscus optical element are binary grating surfaces whose phase profiles φ

are determined by the constants Q, c_n, k_n, d_n, e_n, f_n, and g_n at the bottom of Table 2, the measured quantities being stated in inches as follows;

space="preserve" listing-type="tabular"> TABLE 2 __________________________________________________________________________Lens/ Surface Radius Thickness Material __________________________________________________________________________ 1* 7.99881 0.498000 Ge 2 10.94223 1.66544 Air B 3 -55.5654 0.250000 Ge 4* 20.7530 3.60448 Air C 5 5.10270 0.235813 Ge 6 17.5633 0.126526 Air D 7 -7.03619 0.120000 Ge 8 9.21997 1.00000 Air __________________________________________________________________________*Surface k d e f g __________________________________________________________________________1 0 -0.48613(10.sup.-5) -0.75689(10.sup.-7) -0.11982(10.sup.-8) -0.65944(10.sup.-10) 4 0 0.17374(10.sup.-4) 0.81055(10.sup.-4) 0.73735(10.sup.-4) -0.34511(10.sup.-4).sup. ##STR5## __________________________________________________________________________Surface 2 Surface 3 __________________________________________________________________________Q = 2.6051282(10.sup.6) Q = 2.6051282(10.sup.6) c.sub.1 = 9.147206(10.sup.-2) c.sub.1 = 1.799807(10.sup.-2) c.sub.2 = 9.138846(10.sup.-2) c.sub.2 = 1.799681(10.sup.-2) d.sub.1 = 6.2893(10.sup.-10) d.sub.1 = 6.2893(10.sup.-10) e.sub.1 = -8.1445(10.sup.-12) e.sub.1 = -8.1445(10.sup.-12) f.sub.1 = 2.5868(10.sup.-14) f.sub.1 = 2.5868(10.sup.-14) g.sub.1 = 4.7146(10.sup.-16) g.sub.1 = 4.7146(10.sup.-16) k.sub.1 = k.sub.2 = d.sub.2 = e.sub.2 = f.sub.2 = g.sub.2 k.sub.1 = k.sub.2 =d.sub.2 = e.sub.2 = f.sub.2 = g.sub.2 = 0 φ

= 2π

Q(z.sub.2 - z.sub.1 ) ##STR6## __________________________________________________________________________

14. The telescope system of claim 10, wherein said first negative meniscus optical element and said positive power optical element are affixed to a common housing, said housing being removable from said telescope system, the remaining first positive meniscus optical element and second negative meniscus optical element forming a telescope having a narrower field of view.

15. A telescope system comprising:

(a) a positive meniscus optical element, having a first convex surface and a second concave surface, said first surface being an aspherical surface and said second surface being a binary grating surface, said binary grating surface comprising a plurality of concentric rings, each ring having a series of phase level steps for approximating a Kinoform profile.

(b) a negative meniscus optical element, aligned on a common optical axis behind said positive meniscus optical element.

16. The telescope system of claim 15, wherein said positive meniscus optical element and said negative meniscus optical element are made of germanium, having a useful spectral bandpass for energy in the infrared wavelength region.

17. The telescope system of claim 15, wherein the two optical elements comprise the optical elements A and B, and are shown in FIG. 2 of the drawings as 12 and 56, and wherein said optical elements are fabricated and mounted in accordance with the following prescription Table 1 wherein "Radius" refers to radius of curvature of the optical element surface indicated by the corresponding number, the "Thickness" refers to the distance along the optical axis 0 from the indicated surface to the surface of next highest number, and the materials are as specified, all of the surfaces being spherical except for the positive meniscus optical element whose first surface is aspherical and whose curvature constants c, k, d, e, f, and g are given in the Table 1, and wherein the second surface of the positive meniscus optical element is a binary grating surface whose phase profile φ

is determined by the constants Q, c_n, k_n, d_n, c_n, f_n, and g_n at the bottom of Table 1, the measured quantities being stated in inches as follows;

space="preserve" listing-type="tabular"> TABLE 1 __________________________________________________________________________Lens/ Surface Radius Thickness Material __________________________________________________________________________ 1* 7.99881 0.498000 Ge 2 10.9423 7.02099 Air B 3 -7.03619 0.120000 Ge 4 9.21997 1.00000 Air __________________________________________________________________________*Surface k d e f g __________________________________________________________________________1 0 -0.48613(10.sup.-5) -0.75689(10.sup.-7) -0.11902(10.sup.-8) -0.65944(10.sup.-10) ##STR7## __________________________________________________________________________Surface 2 __________________________________________________________________________Q = 2.6051282(10.sup.6) c.sub.1 = 9.147206(10.sup.-2) c.sub.2 = 9.138846(10.sup.-2) k.sub.1 = 0 k.sub.2 = 0 d.sub.1 = 6.2893(10.sup.-10) d.sub.2 = 0 e.sub.1 = -8.1445(10.sup.-12) e.sub.2 = 0 f.sub.1 = 2.5868(10.sup.-14) f.sub.2 = 0 g.sub.1 = 4.7146(10.sup.-16) g.sub.2 = 0 φ

= 2π

Q(z.sub.2 - z.sub.1) ##STR8## __________________________________________________________________________