A method is proposed to compute and synthesize a microrelief to produce a new nano-optical element for forming 3D images with full parallax at the zero order of diffraction. The synthesis of ...nano-optical elements requires the use of multilevel structures. A method is developed for the first time to compute the phase function of such nano-optical elements. Optical security elements that produce the new security feature are synthesized using electron-beam technology. The accuracy of microrelief formation is 10 nm in terms of depth. A sample optical security element is manufactured, which when illuminated by white light, forms a 3D image at the zero order of diffraction. Photos and video of the new 3D visual effect exhibited by real optical elements are presented. The optical elements developed can be replicated using standard equipment employed for manufacturing security holograms. The new optical security feature is easy to control visually, safely protected against counterfeiting, and designed to protect banknotes, documents, ID cards, etc.
This paper focuses on the development of flat diffractive optical elements (DOEs) for protecting banknotes, documents, plastic cards, and securities against counterfeiting. A DOE is a flat ...diffractive element whose microrelief, when illuminated by white light, forms a visual image consisting of several symbols (digits or letters), which move across the optical element when tilted. The images formed by these elements are asymmetric with respect to the zero order. To form these images, the microrelief of a DOE must itself be asymmetric. The microrelief has a depth of ~ 0.3 microns and is shaped with an accuracy of ~ 10-15 nm using electron-beam lithography. The DOEs developed in this work are securely protected against counterfeiting and can be replicated hundreds of millions of times using standard equipment meant for the mass production of relief holograms.
Abstract
An optical security element forming different 2D images when it is turned by 180 degrees is developed and manufactured for the first time. A synthesis technology is developed that ...incorporates the computation of the beam pattern in elementary hogels with sizes smaller than 100 microns, computation of the phase function of the diffractive optical element (DOE), and formation of the microrelief of the DOE using electron-beam technology. The DOE employed is a multilevel kinoform with an asymmetrical microrelief shaped with a precision of 10 nm. The resulting security feature is easy to control visually, and the DOE is securely protected against counterfeiting. These DOEs are easy to replicate using standard technologies in the manufacturing of embossed holograms and can be used to protect bank notes, securities, and documents against counterfeiting.
A method for computing and synthesizing a diffractive optical element (DOE) on a cylindrical surface is proposed. The computer-generated hologram is a phase reflecting DOE, which, when illuminated ...with white light, displays a 3D image with a 360° viewing angle. The optical element consists of hogels with the size of about 50 microns, which are partly filled with diffraction gratings of various periods and orientations. The DOE is synthesized using electron-beam technology with a resolution of 0.1 micron. Flat optical elements can be replicated using standard equipment employed to produce rainbow relief holograms. When placed on a cylindrical surface, optical elements made on a flexible base display a 3D image observed at 360° viewing angles. The DOE developed can be used to protect objects against counterfeit.
A new method is proposed for computing the microrelief of phase diffractive optical elements (DOEs) forming 2D images with kinematic effects of motion. The DOE is subdivided into elementary areas ...with a size of approximately 50 microns. The synthesis of optical security elements includes the computation of the beam pattern in each elementary area. The beam pattern in each elementary area uniquely defines the phase function of the optical element. The computation of the phase function involves solving a nonlinear operator equation. Efficient methods are developed for computing the microrelief of DOEs forming 2D images with kinematic effects of motion. Sample optical elements are made using electron-beam technology. The microrelief is shaped with a precision of ∼10 nm, and the resolution is equal to ∼0.1 micron. The synthesis method developed is universal in nature. Given different sets of frames, one can achieve different behaviours of the motion of image fragments. The new optical elements can be used to protect banknotes, passports, IDs, and brands against counterfeiting.
A method is proposed to compute and synthesize the microrelief of a diffractive optical element to produce a new visual security feature - the vertical 3D/3D switch effect. The security feature ...consists in the alternation of two 3D color images when the diffractive element is tilted up/down. Optical security elements that produce the new security feature are synthesized using electron-beam technology. Sample optical security elements are manufactured that produce 3D to 3D visual switch effect when illuminated by white light. Photos and video records of the vertical 3D/3D switch effect of real optical elements are presented. The optical elements developed can be replicated using standard equipment employed for manufacturing security holograms. The new optical security feature is easy to control visually, safely protected against counterfeit, and designed to protect banknotes, documents, ID cards, etc.
We demonstrate a new security feature for visual control of the authenticity of optical security features - the change of the images when the optical element is turned by 180 degrees ("switch-180°"). ...The diffractive optical element has an asymmetric microrelief structure resulting from the asymmetry of the scattering pattern. The phase function of the diffractive optical element is computed in terms of Fresnel's scalar wave model. We developed efficient algorithms for computing the structure of flat optical elements to produce the switch effect. A sample of flat optical element for the "switch-180" effect has been developed using electron-beam lithography. The effectiveness of the development is illustrated by the photos and the video captured from a real sample. The visual "switch-180°" effect is easy to control allowing secure anti-counterfeit protection of the optical security feature developed. The new security feature is already used to protect IDs and excise stamps.
A method is proposed to compute and synthesize a nano-optical element to produce a new visual effect: a 3D image formed in the vicinity of zero diffraction order. Usual relief rainbow holograms or ...OVDs can form 3D effect, but at +1 or − 1 diffraction order only and they provide 3D parallax in left/right direction only, and after rotation/inclination of an element, a 3D image changes its color and further disappears completely. The new visual effect provides with full 3D parallax. Moreover, a 3D zero-order image is well visible when an optical element is rotated through 360 degrees; the color of 3D image does not depend on the viewing angle. A synthesis technology is developed incorporating the computation of scattering patterns in elementary areas, computation of the phase function of the entire optical element, and the formation of its microrelief by using e-beam lithography. The microrelief consists of multilevel kinoforms with an accuracy of 10 nm in terms of depth. It was demonstrated by experimental results that the new visual effect is easy for visual perception under white light illumination. A sample of nano-optical element is manufactured, which when illuminated by white light, forms a 3D image in the vicinity of zero-order of diffraction (video available at: https://bit.ly/3QtzxbI).
PDF
