K. M. Mohsin

Quantum realization of some quaternary circuits

We present the design of quaternary quantum version of reversible circuits such as Toffoli gate, modified Fredkin gate, mux, demux, encoder-decoder using linear ion realizable quaternary Muthukrishnan-Stroud gates. Our realization of quaternary Toffoli gate is more efficient than the previous realization and other quaternary circuits are realized for the time in literature.

A Highly Nonlinear Spiral Photonic Crystal Fiber for Tailoring Two Zero Dispersion Wavelengths in the Visible Region

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

Adaptive bilateral filtering for despeckling of medical ultrasound images

In this paper, an adaptive approach of bilateral filtering is introduced for the despeckling of medical ultrasound images. The range parameter is estimated from intensity homogeneity measurements. For each pixel, the measurements are carried out utilizing its local neighbors considering different directions. The range parameter is then estimated from the variance of the most homogeneous blocks and thus, automatically gets adapted according to the variations of the speckle noise. Experiments performed on synthetically-speckled images reveal that the proposed method outperforms several recently introduced despeckling techniques in terms of the signal-to-noise ratio and structural similarity index with a better preservation of image structures. It is shown that the proposed method improves the visual quality of ultrasound images by removing mostly noise while retaining the diagnostically important image details.

Dispersion and nonlinearity properties of a chalcogenide As 2 Se 3 suspended core fiber

A highly nonlinear suspended core fiber (SCF) has been proposed, where a geometrical design parameter called suspension factor (SF) has been used for dispersion tailoring in the infrared region (1.2 μm to 2.8 μm). We have investigated the effect of different suspended conditions of the SCF core on group velocity dispersion, fiber nonlinearity, and power distributions. Peak effective nonlinearity (∼500 W−1 m−1 at 1200 nm with eight air holes) can be varied significantly with SF. The effect of SF on tailoring the zero dispersion wavelengths has been observed. The SF can also be utilized to control mode overlap between core mode and air hole mode for different sensing applications.

Design of a spiral silica photonic crystal fiber for nonlinear applications in visible region

A silica spiral photonic crystal fiber is presented here for tailoring two zero dispersion wavelengths (ZDWs) in the visible region. The proposed fiber has two ZDWs (523.1 and 716.8 nm) along with a very high nonlinearity parameter (1060 W−1 km−1 at 500 nm) around the visible region. The proposed design shows improvement over the group dispersion control and air holes collapsibility of highly air filled hexagonal photonic crystal fiber (HPCF), and low damage threshold of the soft glass photonic crystal fiber. Besides, the low air filling fraction (≈43%) of the proposed design reduces the probability of sustaining higher order modes in the fiber and also ensures easy fabrication due to fewer air holes.

Bilateral filtering with adaptation to phase coherence and noise

In this paper, a bilateral filter with adaptive domain and range parameter is introduced for image denoising. Since the objective of denoising is to reduce noise as much as possible while preserving the perceptually important details, the parameters are adjusted in accordance with perceptual significance of pixels and noise level. The domain parameter is obtained by using the maximum and minimum moments of local phase coherence for being the representative of image details such as edges and corners of an image. The range parameter is estimated from the intensity-homogeneity measurements for their ability to represent the underlying noise. In addition, the filter is applied in an iterative manner to reduce the residual noise. Experiments are carried out using various standard images, and the results show that the proposed method is more effective in reducing additive white Gaussian noise as compared to several recently introduced denoising techniques in terms of the peak signal-to-noise ratio, structural similarity index and visual quality. In addition, experiments performed using real noisy images reveal the ability of the proposed filter to provide denoised images of better visual quality.

Adaptive bilateral filtering for image denoising

In this paper, an adaptive approach for bilateral filtering, based on estimation of the range filtering parameter using homogeneity measurements is introduced for image denoising. For each pixel, the homogeneity measurement is performed utilizing its local neighbors considering different directions, and the range parameter is estimated from the variance of the most homogeneous blocks. In order to reduce the residual noise, the filtering operation is carried out in an iterative manner. A stopping criterion using the structural similarity index is provided. Experiments are carried out using various standard images and the results show that the proposed method is more effective in reducing additive white Gaussian noise as compared to several recently introduced denoising techniques in terms of the peak signal-to-noise ratio and structural similarity index with a reduced computational requirement.

Optical characterization of a chalcogenide glass nanophotonic device

In this paper, we have proposed a nonlinear photonic device and characterized linear and nonlinear optical properties from 1.5 µm to 5 µm using full vector finite element method. A sub-wavelength photonic wire inside a silica glass photonic crystal structure with an average index contrast ≈ 1.4 is found to maintain tight optical confinement at the peak operating wavelength. We have obtained a highly anomalous dispersion region starting from 1.76 µm to a maximum of 4.6 µm. A method to tune the upper zero GVD wavelength has been explored. Again, high anomalous dispersion of pure silica at longer wavelengths has been investigated for the first time. A nonlinearity parameter within the order of 105 W−1 Km−1 also confirms low power mid-IR supercontinuum generation for a pumping wavelength in the short-wavelength infrared band.

Dispersion and birefringence properties of a novel As 2 Se 3 photonic crystal fiber nanowire

In this paper, we have characterized a mid-IR nonlinear photonic device consisting of a highly nonlinear As2Se3 nanowire and a novel photonic crystal structure on silica clad. The lowest optical confinement was found about 60% over the entire bandwidth for an optimum nanowire radius of 600 nm. The highest anomalous GVD obtained was about 1348 ps/nm. km with the lowest anomalous GVD bandwidth of around 2500 nm. The lowest nonlinearity obtained was on the order of 104 W−1 km−1, which ensures that the device is ideal for mid-IR super-continuum (SC) generation. It has been found that a birefringence about 30000 times higher than that of a circular nanowire may be obtained due to only 5% deformation of the nanowire. A relationship between the peak value of birefringence and nanowire ellipticity has been obtained for a certain design parameter. Finally, supercontinuum simulation has been conducted to realize the effects of high anomalous dispersion accompanied by ultra-high nonlinearity.

Design and characterization of a novel spiral photonic crystal fiber nanowire for visible range applications

In this paper, we have proposed a novel nanophotonic device for nonlinear applications in the visible range. The proposed device is a photonic crystal fiber nanowire composed of highly transparent silica with a germania doped silica as core material. Numerical analysis has confirmed that the proposed nonlinear device has a maximum Raman gain coefficient of 1324 W⁻¹km⁻¹ with a nonlinearity parameter of 1144 W⁻¹km⁻¹. Again, the ultra-flattened dispersion slope of −0.0038 ps/nm²-km obtained at wavelength ≈ 584 nm has also validated the efficiency of dispersion control mechanism of the newly proposed spiral photonic crystal fiber structure for nonlinear applications. Later, tunability of Raman effective area and Raman interaction length has been investigated for the proposed nanowire based device in the flat dispersion region.