Artur Sobczyk

3-D-Printed Flat Optics for THz Linear Scanners

THz beam shaping via a single diffractive optical element is used to convert a divergent beam into a focal line segment perpendicular to the optical axis. The novel structure was designed for narrowband applications as a kinoform element and we successfully applied it in active, high-speed, THz linear scanners. The theoretical approach and experimental results are presented.

Power Dissipation in Basic Global Clock Distribution Networks

In the paper power dissipation and maximal frequency of basic global clock distribution networks is analyzed. Basic topologies of trees and meshes were implemented and simulated in AMS CMOS 0.35 mum technology. Also, a circuit of basic ring oscillator was designed. The comparison of power dissipation and maximal working frequency between those structures was performed.

Controllable Local Clock Signal Generator for Deep Submicron GALS Architectures

In the paper a local clock signal generator is presented. The structure was designed in regard to use it in GALS (globally asynchronous locally synchronous) architectures. The circuit was implemented in UMC (United Microelectronics Corporation) 90 nm CMOS technology. Performed post-layout electrical simulations shown that generated frequency can be efficiently controlled in different working conditions with relative error not greater than 13%.

THz Beam Shaping Based on Paper Diffractive Optics

Fast and intensive development of terahertz (THz) technology requires designing dedicated optical elements. Here, we generated complicated THz field distribution thanks to simple binary diffractive optical elements (DOEs) made from paper. The paper fabricated structures are lightweight, inexpensive, feasible for fast-prototyping purposes and they have high transparency in the THz range. Structures were designed and simulated in nonparaxial approach which suppresses the influence of geometrical aberrations and enables large apertures in comparison with their focal lengths. Such DOEs can be used in THz tomography, scanners, radiation sources collimation, focusing and gathering the radiation on the detector.

Analysis of Basic Pausable Local Clock Signal Generator

In this paper local clock signal generator basing on three different ring oscillators is discussed. The structure was designed to verify possibility of local clock signal generation using basic delay stages. General simulations were performed to analyze power dissipation and stability of frequency in regard to temperature, transistor model and layout extraction parameters. All circuits were designed in standard CMOS 0.35 mum technology.

The Time Domain Spectroscopygoniometric setup characterization by the utilization of the plastic diffraction grating

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP