Fresnel zone

About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.

Angular spectrum simulation of X-ray focusing by Fresnel zone plates

Abstract: A computing simulation routine to model any type of circularly symmetric diffractive X-ray element has been implemented. The wavefield transmitted beyond the diffractive structures is numerically computed by the angular spectrum propagation method to an arbitrary propagation distance. Cylindrical symmetry is exploited to reduce the computation and memory requirements while preserving the accuracy of the numerical calculation through a quasi-discrete Hankel transform algorithm, an approach described by Guizar-Sicairos & Gutierrez-Vega [J. Opt. Soc. Am. A, (2004), 21, 53–58]. In particular, the code has been used to investigate the requirements for the stacking of two high-resolution Fresnel zone plates with an outermost zone width of 20 nm.

Proton-exchanged Fresnel lenses in Ti:LiNbO 3 waveguides

Abstract: Fresnel lenses were fabricated by the patterned proton-exchange technique in titanium-diffused lithium niobate waveguides. The large change in refractive index available with the proton exchange allows fabrication of a high-efficiency thin Fresnel lens. Lens characteristics of nearly diffraction-limited focus spot size and efficiency up to 70% were obtained. The use of the lens to construct an integrated-optic rf spectrum analyzer of 1-GHz bandwidth and 2-MHz resolution is also demonstrated.

Analysis of the Relation Between Fresnel Zone and Path Loss Exponent Based on Two-Ray Model

Abstract: In this letter, the underlying factor that leads to the change of path loss exponent n is investigated, using a reasonable and reliable indirect demonstration that is based on the simple two-ray model and a developed multiray model. It is found that the first Fresnel zone is the underlying factor that affects n. n will change only if the situation of the obstacles in the first Fresnel zone changes. The conclusion helps to understand the essences of the propagation.

Dynamic holographic interconnects with analog weights in photorefractive crystals

Abstract: A photorefractive interconnect system with coherently erasable synapses (PISCES) is described. Comparing holographic erasure by intensity and phase modulation of the writing beams, we find that the timeaverage technique is most amenable to system implementation. Calculations derived from a simple model of diffraction show that it is possible to find configurations that maximize the interconnection capacity. The PISCES includes Fresnel zone plates for spot array generation, amplitude and phase spatial light modulators based on liquid crystal technology, and detector arrays, in addition to the photorefractive crystal. Alternatives for each of these elements are described.

Multilayer gratings efficiency: numerical and physical experiments

Abstract: Recently the possibility of focusing, imaging and spectroscopy with Fresnel zones etched on a flat multilayer substrate instead of a curved substrate has been shown. This is now known as Bragg-Fresnel Multilayer lenses (BFML). Lamellar gratings etched in a multilayer (LMG) are the basic type of Bragg-Fresnel optics. In this paper we describe important points in the fabrication, computer simulation, and testing of the LMs. They can be very interesting as a spectroscopic device with a relatively high dispersion and efficiency. We develop a rigorous theory of diffraction combined with the layer-by-layer differential integration numerical method. The agreement with experimentals results obtained for a lamellar grating with several period and various etched depths in a W/Si multilayer is very good. The main result is an increase of the effective extinction depth ( t ext ) in short-period gratings which gives a possibility to increase the absolute diffraction efficiency of the LGM practically from 30% to 60% in the first order with a totally suppressed zero order.