Rotation Invariant Parallel Signal Processing Using a Diffractive Phase Element for Image Compression

We propose a new rotation invariant correlator using dimensionality reduction. A diffractive phase element is used to focus image data into a line which serves as input for a conventional correlator. The diffractive element sums information over each radius of the scene image and projects the result onto one point of a line located at a certain distance behind the image. The method is flexible, to a large extent, and might include parallel pattern recognition and classification as well as further geometrical invariance. Although the new technique is inspired from circular harmonic decomposition, it does not suffer from energy loss. A theoretical analysis, as well as examples, are given.

Simple and Efficient Realization of Transverse Linear Dark Beams by Azimuthal Phase-Shifted Square Zone Plate

Herein, we are about to introduce a novel, reliable and straightforward method to create controllable dark lines employing an azimuthal square zone plate. As a matter of fact, this diffractive element is a square zone plate whose zones are phase-shifted azimuthally. As we illustrate, one way to construct it is combining a square zone plate and radial grating having period m. Considering its focusing behavior, we came to the result that a dark line surrounded by linear bright zones is generated for odd m, as well as a cross-like dark zone is produced when m is even. Furthermore, we illustrate that the length of the dark lines depends on the grating period. Finally, the simulation predictions are verified by experimental results.

Nanooptical elements for visual verification

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.

Design of a hybrid refractive-diffractive telescope for observations in UV

Telescopes are one of the common types of satellite payloads. They are used both for Earth and astronomical observations. By using space telescopes it is possible to eliminate the negative effect of the atmosphere on image quality. Additionally, observations in some spectral ranges can be performed only from space due to absorption of certain wavelengths in the atmosphere. One such range is UV below 300 nm, which is of particular interest when it comes to the investigation of hot objects. Reflective telescopes are commonly used in this spectral range, although many classical designs are limited in their useful field of view to values below 1°. In this paper a hybrid refractive-diffractive telescope design working in a 200 nm – 300 nm spectral range with a field of view 10°×10° is proposed. Its performance is compared to purely refractive and reflective systems and significant improvement in the imaging quality of the system and decrease of its size is shown. The choice of the diffractive element type is explained. Parameters of the systems are based on the requirements for a proposed Polish mission UVSat which aims to enable long-term observations of a large number of stars exhibiting UV variance.

Metasurface-generated complex 3-dimensional optical fields for interference lithography

Fast, large-scale, and robust 3-dimensional (3D) fabrication techniques for patterning a variety of structures with submicrometer resolution are important in many areas of science and technology such as photonics, electronics, and mechanics with a wide range of applications from tissue engineering to nanoarchitected materials. From several promising 3D manufacturing techniques for realizing different classes of structures suitable for various applications, interference lithography with diffractive masks stands out for its potential to fabricate complex structures at fast speeds. However, the interference lithography masks demonstrated generally suffer from limitations in terms of the patterns that can be generated. To overcome some of these limitations, here we propose the metasurface-mask–assisted 3D nanofabrication which provides great freedom in patterning various periodic structures. To showcase the versatility of this platform, we design metasurface masks that generate exotic periodic lattices like gyroid, rotated cubic, and diamond structures. As a proof of concept, we experimentally demonstrate a diffractive element that can generate the diamond lattice.

Thermal lens effect and fluorescence of motor oil investigated by holographic method

This paper presents studies of the thermal lens effect in the volume of motor oil by holographic methods using excitation of 447[Formula: see text]nm laser wavelength. The possibility of using a hologram of initial object, as a diffractive element, for obtaining the spectral dependence of the fluorescence of the oil product was shown.

Computer synthesis of diffractive optical elements for forming 3D images

Предложен метод расчета и синтеза микрорельефа дифракционного оптического элемента, формирующего новый визуальный защитный признак - эффект смены одного 3D-изображения на другое 3D-изображение при повороте дифракционного оптического элемента на 90 градусов. Разработаны эффективные алгоритмы расчета микрорельефа дифракционного оптического элемента. Методами математического моделирования определены оптимальные параметры дифракционного оптического элемента. С помощью электронно-лучевой технологии изготовлены образцы оптических защитных элементов, формирующих визуальный эффект смены 3D-изображений при освещении оптического элемента белым светом. Разработанные оптические элементы могут тиражироваться с помощью стандартного оборудования, используемого для изготовления защитных голограмм. Новый защитный признак легко контролируется визуально, надежно защищен от подделки и предназначен для защиты банкнот, документов, идентификационных карт и др. A method is proposed to compute and synthesize the microrelief of a diffractive optical element to produce a new visual security feature: alternation of two 3D color images when the diffractive element is rotated by 90 degrees. Effective algorithms for computing the micro-relief of an optical element are developed. Optimal parameters of the diffractive optical element are determined using methods of mathematical modeling. Sample optical security elements that produce 3D to 3D visual switch effect when illuminated by white light were manufactured using the electron-beam lithography. The optical elements developed can be replicated using a 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.