Krzysztof Perlicki

Impact of alien wavelength on wavelength division multiplexing transmission quality

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

Optoelectronic systems for automatic vehicle counting and classification in rest areas

The following paper depicts an architectural layout and operational insights towards an optoelectronic system dedicated for vehicle counting and classification, designed to monitor occupancy of rest areas. The system is based upon an image cue acquisition by video cameras and advanced signal processing mechanism. In order to satisfy the appropriate realization of measurement procedure (counting and classification), a specific measurement configuration scheme alongside optimized video stream capturing parameters were set up. Concerning signal processing methods, the most effective and appropriate for the purpose of vehicle counting and classification were selected. Moreover, the article presents the outcomes of the designed measurement campaign conducted on the S7 expressway within the agenda of the National Center for Research and Development RID project. The results obtained with use of the designed methodology were compared to the outcomes of the manual method.

Simple analysis of the distribution of birefringence in fiber optics links

In this paper, a simplified analytical method to evaluate an optical fiber birefringence was presented. It allows a significant simplification of the measurement of the spatial distribution of birefringence in optical fiber links; particularly for the small value of the birefringence. The birefringence distribution may be deduced from the calculation of the round-trip Mueller matrices derived from only two power evolution traces corresponding to the angles of the polarizer

Polarization tracking based on Stokes curve analysis

A method to recognize polarization sets is proposed. Presented method is based on analysis of torsion and curvature of three-dimensional curve. The space curve is defined by states of polarization on the Poincare sphere

Investigation of the distribution of the states of polarization on the poincare' sphere using the spherical radial distribution function

A new method for characterization of the distribution of the states of polarization on the Poincare sphere is described. Analysis of the state of polarization distribution is based on spherical radial distribution function

Analysis of clusters and uniformity of distribution of states of polarization on the Poincaré sphere

An analysis of the clusters and the uniformity of distribution of states of polarization on the surface of a Poincaré sphere generated by rotating wave plates is given. The analysis of clusters of the states of polarization is based on a spherical radial distribution function. For uniform analysis of the distribution, two methods are proposed. The first method is based on calculation of the correlation coefficient; the second method is based on calculation of the angles between pairs of the states of polarization on the Poincaré sphere. For polarization scramblers consisting of eight or more rotating wave plates, nonclustered and near-uniform distribution of states of polarization is obtained.

Stability evaluation of polarization pulling based on stimulated Raman scattering

Evaluation of polarization control stability by means of stimulated Raman scattering in optical fiber is presented. In order to find optimal hardware setup, proper simulations are performed to evaluate polarization stability depending on input signal and pump SOP, pump power, length and nonlinearity of the fiber. Results are useful for polarization attractor configuration choice, depending on what parameter is to be optimized.

Experimental verification of distributed temperature sensor model based on spontaneous Raman scattering

Mathematical model of distributed temperature sensor based on spontaneous Raman scattering is described in this paper. The concept uses Stokes and anti-Stokes scattered signals as reference and detection signals respectively. Model is completed by experimental results coming from setup of 200 m G.652 sensing fiber tested in temperatures 3°C, 15°C, 23 °C and 30°C and 2500 m reference fiber preserved in 22°C. Parameters of the scattered signal source in used setup configuration allow to achieve distributed temperature profile with spatial resolution up to 50 m.

Impact of transmission parameters on Nyquist WDM system

In this paper the analysis of the transmission quality in Nyquist WDM transport system is presented. Results are presented of a system simulation carried out for different modulation format, symbol rates, channel spacing and filter characteristics of the transmitter and receiver. This paper also contains the comparison between results obtained for the N-WDM (Nyquist Wavelength Division Multiplexing) and DWDM (Dense Wavelength Division Multiplexing) system. Two quality indicators are taken into consideration: interchannel crosstalk and symbol error rate for both different system configurations.

Polarization pulling based on stimulated Raman scattering for polarization division multiplexing system

Numerical modelling of the Raman polarization attraction and amplification process in the telecommunication band around 1550 nm is presented. Possibility of achieving both polarization pulling and amplification in Polarization Division Multiplexing transmission system by exploiting the polarization dependence of stimulated Raman scattering is investigated. Analysis is made both for co- and counter- propagation configuration with standard and highly nonlinear fiber. Different input pump polarization states are tested for best polarization pulling effectiveness.