The self-focusing Fresnel-Dammann grating and the Fresnel binary CGH for compact 2-D light spot array generation

The authors have described the design and demonstrated the performance of two types of lensless array generator. The Self-focusing Fresnel-Dammann grating (SFD), and the Fresnel hologram. The SFD is based on a conventional Dammann grating, but obviates the need for extraneous Fourier transform lenses, by combining the grating with a Fresnel zone plate, in an exclusive-OR fashion. No alignment is required and no bulky or dispersive refractive elements are used. The Fresnel hologram can be designed for high fanout, but the design must take into account the phases of the light spots in the image array. The authors have demonstrated this for an 8times8 fanout element, where a set of random phases in the output gave rise to a satisfactory performance, whilst another set of phases gave an undesired, although interesting, result. The authors have also demonstrated a 30deg slanted axis, random phase design, generating a two dimensional array of 8times8 beams, used in reflection, and operating in a multiple reflection, planar-optic configuratio

The non-coplanar baselines effect in radio interferometry: The W-Projection algorithm

We consider a troublesome form of non-isoplanatism in synthesis radio telescopes: non-coplanar baselines. We present a novel interpretation of the non-coplanar baselines effect as being due to differential Fresnel diffraction in the neighborhood of the array antennas. We have developed a new algorithm to deal with this effect. Our new algorithm, which we call "W-projection", has markedly superior performance compared to existing algorithms. At roughly equivalent levels of accuracy, W-projection can be up to an order of magnitude faster than the corresponding facet-based algorithms. Furthermore, the precision of result is not tightly coupled to computing time. W-projection has important consequences for the design and operation of the new generation of radio telescopes operating at centimeter and longer wavelengths.Comment: Accepted for publication in "IEEE Journal of Selected Topics in Signal Processing

Information Storage and Retrieval for Probe Storage using Optical Diffraction Patterns

A novel method for fast information retrieval from a probe storage device is considered. It is shown that information can be stored and retrieved using the optical diffraction patterns obtained by the illumination of a large array of cantilevers by a monochromatic light source. In thermo-mechanical probe storage, the information is stored as a sequence of indentations on the polymer medium. To retrieve the information, the array of probes is actuated by applying a bending force to the cantilevers. Probes positioned over indentations experience deflection by the depth of the indentation, probes over the flat media remain un-deflected. Thus the array of actuated probes can be viewed as an irregular optical grating, which creates a data-dependent diffraction pattern when illuminated by laser light. We develop a low complexity modulation scheme, which allows the extraction of information stored in the pattern of indentations on the media from Fourier coefficients of the intensity of the diffraction pattern. We then derive a low-complexity maximum likelihood sequence detection algorithm for retrieving the user information from the Fourier coefficients. The derivation of both the modulation and the detection schemes is based on the Fraunhofer formula for data-dependent diffraction patterns. We show that for as long as the Fresnel number F<0.1, the optimal channel detector derived from Fraunhofer diffraction theory does not suffer any significant performance degradation.Comment: 14 pages, 11 figures. Version 2: minor misprints corrected, experimental section expande

Lateral and axial resolution criteria in incoherent and coherent optics and holography, near- and far-field regimes

This work presents an overview of the spatial resolution criteria in classical optics, digital optics and holography. Although the classical Abbe and Rayleigh resolution criteria have been thoroughly discussed in the literature, there are still several issues which still need to be addressed, for example the axial resolution criterion for coherent and incoherent radiation, which is a crucial parameter of three-dimensional (3D) imaging, the resolution criteria in the Fresnel regime, and the lateral and axial resolution criteria in digital optics and holography. This work discusses these issues and provides a simple guide for which resolution criteria should be applied in each particular imaging scheme: coherent/incoherent, far- and near-field, lateral and axial resolution. Different resolution criteria such as two-point resolution and the resolution obtained from the image spectrum (diffraction pattern) are compared and demonstrated with simulated examples. Resolution criteria for spatial lateral and axial resolution are derived, and their application in imaging with coherent and incoherent (noncoherent) waves is considered. It is shown that for coherent light, the classical Abbe and Rayleigh resolution criteria do not provide an accurate estimation of the lateral and axial resolution. Lateral and axial resolution criteria based on an evaluation of the spectrum of the diffracted wave provide a more precise estimation of the resolution for coherent and incoherent light. It is also shown that resolution criteria derived in approximation of the far-field imaging regime can be applied for the near-field (Fresnel) regime