Athermalized diffractive optical elements
First Claim
1. A method of manufacturing an optical element from a light transmissive body of material, subject to changes in dimension with temperature, which method comprises the steps ofdetermining the nominal location of a plurality of lines on a surface of said body to define the nominal widths of successive zones of a diffractive optical element (DOE);
- specifying an actual spacing between adjacent ones of said lines which define the zones of said DOE, said actual spacing being a function of the dimensional changes of said material with temperature such that at least some of the zones of said DOE approach their nominal widths in response to temperature changes in an amount sufficient to athermalize said DOE across a range of temperature; and
forming zones on a surface of said body in accordance with said actual spacing, whereinsaid nominal zone widths are determined at a certain temperature between the lower, colder temperature and the upper, hot temperature ends of said range; and
said actual spacings define at least some zones of increased width and some zones of decreased width, with respect to said nominal zone widths at said certain temperature.
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Abstract
A diffractive optical element, ("DOE"), and particularly a diffractive lens having annular zones about an optical axis and known as a Fresnel zone plate or kinoform lens, is athermalized so that its effective focal length ("EFL") does not shift substantially with temperature over a temperature range by, respectively, increasing and decreasing the zone widths with respect to widths which are optimized to focus at the EFL at room temperature. Half of the zones (alternate, adjacent zones) provide the correct EFL for the expanded condition of the lens at the hot end of the temperature range; the other half of the zones provide correct EFL for the contracted condition of the lens at the cold end of the temperature range. The exact spacings and zone widths are obtained, in the same manner as a diffractive lens is corrected for spherical and chromatic aberration, from the coefficients of the equation governing the phase shift through the lens as a function of radial distance from the optical axis, by averaging the aberration properties at the hot and cold ends of the range, the net effect of which is to dictate the spacing of alternate, successive zones which are slightly greater and less than the zone spacings optimized at room temperature, respectively.
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Citations
30 Claims
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1. A method of manufacturing an optical element from a light transmissive body of material, subject to changes in dimension with temperature, which method comprises the steps of
determining the nominal location of a plurality of lines on a surface of said body to define the nominal widths of successive zones of a diffractive optical element (DOE); -
specifying an actual spacing between adjacent ones of said lines which define the zones of said DOE, said actual spacing being a function of the dimensional changes of said material with temperature such that at least some of the zones of said DOE approach their nominal widths in response to temperature changes in an amount sufficient to athermalize said DOE across a range of temperature; and forming zones on a surface of said body in accordance with said actual spacing, wherein said nominal zone widths are determined at a certain temperature between the lower, colder temperature and the upper, hot temperature ends of said range; and said actual spacings define at least some zones of increased width and some zones of decreased width, with respect to said nominal zone widths at said certain temperature. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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- 17. A diffractive optical element (DOE) which comprises a light transmissive body of material subject to changes in dimension with temperature, a plurality of lines on a surface of said body which define a grating having a plurality of zones, successive ones of which zones are adjacent each other, and the spacings between said lines which define the widths zones differing from each other in an amount sufficient to athermalize said DOE across a range of temperature, wherein at least some of the zones have a width greater than their nominal zone widths at a certain temperature, and at least some of the zones have a width less than their nominal zone widths at said certain temperature, said certain temperature being between the lower, cold temperature and the upper, hot temperature ends of said range.
Specification