Small aperture multifocal

Claim 2

An optical device possessing the Cohen lens design utilizing a phase zone plate that accommodates a small pupil size.

Claim 3

The optical device of claim 1 wherein the device includes an optical element containing a phase zone plate containing annular concentric zones possessing blazed facets which splits light to at least two distinct focal points utilizing a minimum number of alternating stepped repetitive patterns in accordance with √k spacing.

Claim 4

The optical device of claim 2 wherein the element encompasses a diffractive bifocal optical element comprising a phase zone plate containing annular concentric zones in which the zones are spaced substantially propor­tional to √k, the odd zones possessing blazed facets with an optical path length (depth) one-half the optical path length (depth) of the even facets and discon­tinuous jumps in the profile only at the odd radii.

Claim 5

The optical device of claim 3 wherein the element splits the light into two focal points even when restricted by an aperture stop of about one full-period zone.

Claim 6

The optical device of claim 4 wherein the element contains a multiple focal point profiled phase zone plate which provides two or more distinct focal points even when used with aperture stops as small as one full-period zone, the phase zone plate has blazed facets comprising a plurality of annular concentric zones spaced according to the formula r k =√ constant x k , where k is a zone and is equal to 1, 2, 3, etc., as the zones progress from the central axis of the phase zone plate to the periphery of the phase zone plate, in accordance with the Cohen lens design, r k is the half-period zone radii, with the zones and zone radii being odd or even in accordance with the value of k as k alternates progressively odd and even from the central axis to the periphery of the phase zone plates, the depth of the odd half-period zones is about one-half the depth of the even half-period zones and each interface between an odd and even half-period zone at the even zone radli r k , in which case k is an even number, exhibits a continuous profile with no discontinuous step.

Claim 7

The optical device of any one of claims 1 to 5 containing a repetitive profile in the phase zone plate wherein the repetitive profile is given by d = D₀ · {1/2 + 1/2 · cos (π · r²/b²)} where D₀ = 0.405 · λ/(η-1).

Claim 8

The optical device of any one of claims 1 to 5 containing a parabolic repetitive profile in the phase zone plate.

Claim 9

The optical device of any one of claims 1 to 7 in the form of either an intraocular or contact lens.