Abstract: In a secure imaging system for securing documents or encrypting images, an image comprises an array of printed positions formed using a group of inks each having a predetermined spectrum. The positions are selected to form a predetermined image, either real or virtual, when the image is viewed through an optical processor. An image formed using inks having the same colors as experienced by the human eye, but not sharing exactly the same spectra, will fail to form the correct predetermined image.

Abstract: A simultaneous multifocal contact lens for correcting vision acuity of an individual is disclosed.

Abstract: A progressive multifocal lens for eyeglasses formed along a principle meridian curve, with a farsighted vision zone (1) having an optical power corresponding to that required for viewing distant objects, a nearsighted vision zone (3) having an optical power corresponding to that required for viewing near objects, and an intermediate vision zone (2) between and progressively connecting the farsighted vision zone and the nearsighted vision zone, includes a transparent, non-rotationally-symmetrical, microrelief structure in one or more of these vision zones.

Abstract: A tri-focal diffractive lens defining three foci, for viewing a band of light having a representative wavelength of .lambda., including a diffractive surface having a number of optical heights, h.sub.o, wherein the difference between the highest and the lowest optical heights is, modulo .lambda., substantially different from .lambda./2, wherein each of the foci receives at least 20% of light incident on the lens.

Abstract: An infrared detector including a sensor which provides an output signal responsive to infrared radiation incident on a face thereof, and a diffractive optical element which directs a substantial portion of incident visible radiation away from the sensor and which has substantially no diffractive effect on incident infrared radiation.

Abstract: A diffractive optical element and a method to produce same is disclosed. The optical element comprises a base and at least first and second phase zones wherein the first phase zone comprises a first multiplicity of steps and the second phase zone comprises a second multiplicity of steps and wherein the first multiplicity and the second multiplicity of steps are different. The method to produce the diffractive optical element of the present invention includes the step of defining a collection of masks for creating stepped phase zones wherein at least one of the collection of masks partially masks out at least one phase zone such that the at least one phase zone will be partially etched.

Abstract: There is disclosed a diffractive optical element and a method to produce same wherein the element comprises a base and at least one phase zone comprising an arbitrary multiplicity M of steps of generally identical step height, wherein M is not a power of 2. The method includes the steps of defining a basic depth unit equivalent to a zone height divided by M, defining a depth sequence of N depths wherein N is the smallest integer greater than log.sub.2 M such that each of the M steps can be produced by at least one linear combination of the N depths, defining N masks herein each mask enables the optical element to be processed to one of the N depths and wherein for each mask, the steps to be processed are those which have the one of the N depths in its linear combination and serially utilizing each of the N masks for processing of the optical element.