Diffractive optical element and optical system incorporating the same
First Claim
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1. A diffractive optical element, comprising:
- a substrate; and
a diffraction grating formed on the substrate, the pitch of said diffraction grating varying such that it progressively decreases outward over one region extending outward from a center towards a predetermined position and is then, in another region extending outward from the predetermined position towards the extremity of said diffraction grating, kept substantially constant, wherein the pitch of said diffraction grating varies according to a spline function as the phase distribution function of said diffractive optical element.
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Abstract
A diffractive optical element, as well as an optical system incorporating the same, has a comparatively large minimum grating pitch and, hence, is easy to produce. The diffractive optical element has a diffraction grating surface and an aspherical surface formed on an identical substrate or on separate substrates. The pitch of the diffractive grating varies such that it progressively decreases radially outward from the center of the substrate and then kept constant towards the radially outer extremity of the substrate.
28 Citations
13 Claims
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1. A diffractive optical element, comprising:
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a substrate; and
a diffraction grating formed on the substrate, the pitch of said diffraction grating varying such that it progressively decreases outward over one region extending outward from a center towards a predetermined position and is then, in another region extending outward from the predetermined position towards the extremity of said diffraction grating, kept substantially constant, wherein the pitch of said diffraction grating varies according to a spline function as the phase distribution function of said diffractive optical element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
a diffractive optical element according to claim 1.
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7. An exposure apparatus comprising:
an optical system according to claim 1, wherein a device pattern is transferred on a wafer by the light through said optical system.
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8. A process for producing a device, comprising the steps of:
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transferring a device pattern onto a resist on the wafer through the exposure apparatus of claim 7; and
developing the wafer.
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9. An optical system comprising:
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a first substrate having a diffraction grating, the pitch of said diffraction grating varying such that it progressively decreases outward over one region extending outward from a center towards a predetermined position and is then, in another region extending outward from the predetermined position towards the extremity of said diffraction grating, kept substantially constant; and
a second substrate having a surface which comprises an aspherical surface formed in a region corresponding to said another region and a spherical or flat surface formed in a region corresponding to said one region, wherein the pitch of said diffraction grating varies according to a spline function as the phase distribution function of said diffractive optical element. - View Dependent Claims (10, 11, 12, 13)
an optical system according to claim 9, wherein a device pattern is transferred on a wafer by the light through said optical system.
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13. A process for producing a device, comprising the steps of:
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transferring a device pattern onto a resist on the wafer through the exposure apparatus of claim 12; and
developing the wafer.
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Specification