Optical systems employing stepped diffractive surfaces
AssigneeKSM Associates, Inc.
InventorYakov G. Soskind
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Abstract
Stepped diffractive surfaces (13) are used to reduce variations in the optical properties of an optical system as a result of a change in the temperature of all or a portion of the system. Such surfaces have optothermal coefficients which differ from the optothermal coefficients of both kinoforms and refractive elements. Accordingly, stepped diffractive surfaces can be combined with such elements to achieve overall thermal control of optical systems employing such elements.
Claims25
A method for at least partially controlling a change in an optical property of an optical system resulting from a change in the temperature of at least a portion of the system, said system having an optical axis and comprising at least one lens element having an index of refraction, a shape, and a location within the optical system, said method comprising:
- (A) including at least one stepped diffractive surface in the system, said at least one stepped diffractive surface comprising N concentric planar zones which:
- (i) are orthogonal to the system's optical axis,
- (ii) are displaced from one another along the optical axis, the displacement between zone i and zone i+1 being di, and
- (iii) define a base curve, said stepped diffractive surface having a clear aperture and a sag which changes monotonically from the optical axis to the clear aperture;
- and
- (B) selecting the base curve and the di at least in part to compensate for a change in the index of refraction, shape, and/or location of said at least one lens element as a result of said change in temperature to at least partially control the change in the optical property.
A method for at least in part controlling a change in an optical property of an optical system resulting from a change in the temperature of at least a portion of the system, said system having an optical axis and a nominal operating wavelength λ0, and comprising at least one lens element having an index of refraction, a shape, and a location within the optical system, said method comprising:
- (A) including at least one stepped diffractive surface in the system, said at least one stepped diffractive surface:
- (i) separating a first medium having an index of refraction n1 from a second medium having an index of refraction n2;
- (ii) having a working diffractive order “j” which may be constant or variable;
- and
- (iii) comprising N concentric planar zones orthogonal to the system's optical axis which define a base curve, said zones satisfying the relationship:
- |di≡jλ0/|(n2−n1)|, for i=1 to N−1,
- where di is the displacement along the optical axis between zone i and zone i+1;
- and
- (B) selecting the base curve and the di at least in part to compensate for a change in the index of refraction, shape, and/or location of said at least one lens element as a result of said change in temperature to at least partially control the change in the optical property.
An optical system which has an optical axis and an operating temperature within a range of temperatures, said system comprising:
- (a) at least one stepped diffractive surface which comprises N concentric planar zones which:
- (i) are orthogonal to the system's optical axis,
- (ii) are displaced from one another along the optical axis, the displacement between zone i and zone i+1 being di, and
- (iii) define a base curve, said stepped diffractive surface having a clear aperture and a sag which changes monotonically from the optical axis to the clear aperture;
- (b) at least one optical surface which (i) is not a stepped diffractive surface and (ii) has a non-zero optical power;
- and
- (c) a housing which supports the at least one stepped diffractive surface and the at least one optical surface;
- wherein the at least one stepped diffractive surface compensates for changes in the at least one optical surface and/or the housing as a result of changes in the system's operating temperature.
An optical system which (i) has an optical axis, (ii) has a nominal operating wavelength λ0, and (iii) has an operating temperature within a range of temperatures, said system comprising:
- (a) at least one stepped diffractive surface which:
- (i) separates a first medium having an index of refraction n1 from a second medium having an index of refraction n2;
- (ii) has a working diffractive order “j” which may be constant or variable;
- and
- (iii) comprises N concentric planar zones orthogonal to the system's optical axis which define a base curve, said zones satisfying the relationship:
- |di|≡jλ0/|(n2−n1)|, for i=1 to N−1,
- where di is the displacement along the optical axis between zone i and zone i+1;
- (b) at least one optical surface which (i) is not a stepped diffractive surface and (ii) has a non-zero optical power;
- and
- (c) a housing which supports the at least one stepped diffractive surface and the at least one optical surface;
- wherein the at least one stepped diffractive surface compensates for changes in the at least one optical surface and/or the housing as a result of changes in the system's operating temperature.
An optical element comprising two optical surfaces wherein:
- (a) one of the optical surfaces comprises a stepped diffractive surface formed in a substrate, said stepped diffractive surface having an optothermal coefficient which depends on dn/dT, where n is the index of refraction of the substrate and T is temperature;
- (b) the other of the optical surfaces (i) is not a stepped diffractive surface and (ii) has a non-zero optical power;
- (c) the stepped diffractive surface compensates for changes in the other optical surface as a result of changes in the element's temperature;
- and
- (d) at a nominal wavelength λ0, the stepped diffractive surface has zero paraxial power.
Dependencies are inferred from the claim text.