Contributed papers
Local image processing is about performing a basic group of simple arithmetic and logic operations on a limited neighbourhood of every pixel in 2D-represented data. The parallel architecture of optoelectronic processors makes these machines especially well suited to perform such local operations. In this paper we present some possible architectures of such processors and a proof-of-principle demonstrator based on present-day technology. We discuss applications and highlight limitations.
The paper provides an overview of optical methods for 3D shape measurement. Then, the hybrid methodology based on integrated structured light/photogrametry system and spatio-temporal phase fringe pattern analysis is presented for static and variable in time true 3D-object measurement. The algorithms for clouds of point patching and their triangulation are described as well as the procedures for adding the texture (R, G, B) information. Finally, several applications including implementation of 3D data in CAD/CAM/rapid prototyping systems and computer graphics/animation software are presented.
We report on the design, the fabrication, the characterization
and the demonstration of scalable multi-channel free-space interconnection
components with the potential for Tb/s.cm2 aggregate bit rate capacity
over inter-chip interconnection distances. The demonstrator components
are fabricated in a high quality optical plastic, PMMA, using an ion-based
rapid prototyping technology that we call deep proton lithography.
With the presently achieved Gigabit/s data rates for each of the individual
16 channels with a BER smaller than 10-13 and with inter-channel cross-talk
lower than -22dB the module aims at optically interconnecting 2-D opto-electronic
VCSEL and receiver arrays, flip-chip mounted on CMOS circuitry.
Furthermore, using ray-tracing software and radiometric
simulation tools, we perform a sensitivity analysis for misalignment and
fabrication errors on these plastic micro-optical modules and we study
industrial fabrication and material issues related to the mass-replication
of these components through injection-molding techniques. Finally we provide
evidence that these components can be mass-fabricated in dedicated, highly-advanced
optical plastics at low cost and with the required precision.
We will discuss the recent developments in the field of guided-wave MOEMS. The goal will be to review the processes involved in the fabrication of silicon-based optical waveguides and will proceed to describe and analyse how this photonic technology may be integrated within the MEMS environment. Finally, some examples of optical functions that can benefit by the integration of optical waveguides with MEMS will be described, such as integrated optic switches, integrated optical modulators, micromachined optical sensors, and microprobes for optical near-field microscopy.
Touted as promising components for present and future data-communication and sources for photonic switching fabrics, vertical-cavity surface-emitting lasers (VCSELs) have been studied in detail during the past years, with a focus on their static light-current and dynamic intensity modulation characteristics. Their superior beam quality, low power consumption, Gigahertz modulation bandwidth and the possibility of manufacturing these devices in 2D arrays are often cited as substantial advantages compared to traditional edge-emitting semiconductor lasers or light emitting diodes. A disadvantage of VCSELs is that the polarisation of the emitted light is not defined a priori due to the VCSEL’s quasi-cylindrical symmetry and its direction of lasing perpendicular to the active region. However, real VCSELs do emit linearly polarised light and often polarisation switching from one state to the orthogonal one is observed as the current is changed. In this contribution we will discuss the experimental characteristics of this intriguing polarisation switching phenomenon. We will give an overview of various physical mechanism proposed to explain the polarisation behaviour of these devices and we will illustrate the use of this polarisation switching in the implementation of reconfigurable optical interconnects.
Optical fields generated in complex multilayered structures of modern semiconductor optoelectronic devices are described in the present paper using the vertical-cavity surface-emitting laser (VCSEL) as an example. Usually scalar theoretical approaches starting from the scalar wave equation ensures sufficient exactness of modeling of VCSEL optical fields. In the case of microresonator lasers as well as in more exact modeling of a VCSEL operation, however, the full vector approaches are necessary to be applied. Interactions between optical and other (i.e. mainly electrical, thermal and mechanical) physical phenomena inside VCSEL resonators are also described. Their role is particularly important in highly excited devices when physical phenomena taking place inside their volumes are strongly interrelated with one another.
The paper presents selected realisations of liquid crystal fibre optic systems utilising liquid crystal cells and liquid crystal waveguides with potential application in optical information processing. In particular, linear systems with polarisation modulation and also nonlinear phenomena in liquid crystal waveguides are analysed. The paper summarises original achievements of the Faculty of Physics, Warsaw University of Technology in applications of optical fibre waveguides and liquid crystal systems to obtain cross-talk free and highly parallel architectures of optical computing systems.
Beam reflection at a focusing nonlinear-linear interface near critical incidence of total internal reflection is analysed. Basics of the three-dimensional formulation of the problem are outlined. Numerical simulations of the beam reflection are presented. It is shown that owing to cross focusing and deformations of incident and reflected beams, a bistable switch is possible to achieve. Characteristic features of this switch are discussed.
We investigated the formation and interaction of bright spatial solitons in photorefractive nonlinear media. We demonstrate soliton formation, self-bending, coherent and incoherent collision resulting in energy exchange, soliton fusion, birth of new solitons and anomalous repulsion of solitons. The results on formation of multi-component incoherent solitons (vector solitons) are presented.
The aim of this work is presentation of principles of work and properties of multimode interference (MMI) structures and their basic applications in optoelectronic circuits. We discuss the principles of simple, mirrored and multiple images formation paying attention to imaging quality, tolerance, losses, and power division in output signals. On the base of it, MMI applications in integrated optic systems - in splitters and couplers N´M technology, modulators and switches in Mach-Zehnder configuration and multiplexers are considered. The possibility of MMI production in gradient-index waveguides made by ion exchange in glass is also presented.
The paper presents automatic recognition of images using the diffraction pattern sampling. This method, based on properties of Fourier transform, utilises special shapes of sampling element and gives the possibility to deal with data invariant with respect to typical transformation (shift, rotation and scaling) of the input images. Furthermore, if computer-generated hologram is used as feature extractor, instead of commercially available ring-wedge detector, then the process of feature extraction can be optimised with a method proposed by the authors. The method uses rough set theory for objective function definition and stochastic evolutionary algorithms for space search. The features obtained by optimised sampling of the diffraction pattern are the input data for the semantic classifier. Since noise present in images has got typically Gaussian distribution, therefore classification should be made in the model with statistical uncertainty. For this purpose artificial neural network is used. The presented method is illustrated with experiments of speckle pattern recognition performed with optimised and standard computer-generated holograms. The experiments confirmed good overall accuracy of the optimised system outperforming the results obtained for standard one by a factor of two to five.
We review basic techniques for generation of ultra-short light pulses. In particular, we discuss different methods of mode-locking, pulse amplification and frequency conversion methods based on the 2nd and 3rd order nonlinear processes. Basic methods for pulse characterisation are also discussed.
Evolutionary artificial neural networks have gradually evolved as a new field at the junction of artificial neural networks and evolutionary algorithms. Rapid growth of both fields could be observed in the last few years. However, limitations in neural networks techniques can diminish the potential of neural networks. Some of these limitations can be treated as optimisation problems. As a consequence, evolutionary algorithms can be used to overcome these deficiencies of traditional neural network methods. The primary objective of this paper is to highlight the most important features of evolutionary algorithms and the way they can be used to increase the efficiency of neural networks techniques. It is assumed that the reader is familiar with the basic concepts of neural networks.
In many works, the magneto-optical effects for optical frequencies are normally described by using an electric dipole approximation. Nevertheless, this approximation is problematic in far infrared region and for ultrathin films in the optical band. For this reason, dispersion relations have been derived for guided modes in a monolayer system at transverse geometry with bi-gyrotropic anisotropy on the base of matrix elements. The permeability tensor effect on waveguiding is analysed in detail. Experimental possibilities of the dark mode spectroscopy for permeability tensor study in mentioned structures are briefly discussed.
The paper presents fabrication technology of planar gradient tapered waveguide structures using the ion exchange technique in glass. Theoretical predictions of model properties have been compared with experimental results. Application possibilities of these waveguides in sensor related techniques have been pointed too.
The performance of P-on-n double-layer heterojunction (DLHJ) HgCdTe photodiodes at temperature of 77 K is presented. The effect of inherent and excess current mechanisms on quantum efficiency and R0A product is analysed. The diodes with good R0A operability, high quantum efficiency, and low 1/f noise have been demonstrated at cutoff wavelengths up to 14 mm. The experimental results show that proper surface passivation and low series/contact resistance are major issues relating to fabrication of HgCdTe detectors with high performance.
Application of degenerate self-imaging filters, instead of exact self-imaging filters, to generate a complete basis of a function space for propagated light fields, has been tested. Correlation of original images and those reconstructed in such a space has showed satisfying results for a basis consisting of merely four degenerate self-imaging orthogonal eigenfunctions.
The present article is an attempt to answer the question whether it is possible to use optical correlation for analysis of a composite input scene. There are two possible approaches to traditional optical correlation setups with a thin hologram used for recognising objects in the input scene. In the first case, one input scene object out of several others is recognised. In the second case, only one object is searched for among numerous other objects in an input scene. This paper presents a suggestion on how to increase the range of traditional optical correlation systems with a thin hologram for analysis of a composite input scene.
Preliminary research on structural quality of bismuth germanium oxide (BGO) and bismuth silicon oxide (BSO) is reported. X-ray rocking curves, high resolution diffraction mapping, and plane wave reflection topography is used in order to relate performance of the planned photonic device to crystalline characteristics of the samples.
In the paper the methodology of three-dimensional measurement of refractive index distribution in optical phase microelements is presented. Tomographic interferometry, known from macro-scale measurements, has been conformed to fulfil micro-scale requirements. The results of experimental studies have been presented, with special emphasis focused on the system design, especially on the problem of well-aligned rotation of microelement. The proposed solution reduces effective radial run-out to submicron values. For demonstration of system performance, reconstruction of three-dimensional refractive index distribution in a fused, optical fibre joint has been performed. The discussion of reliability and limitations of the method is given. Results have proven the system as powerful measurement tool for 3D refractive index distribution in optical fibres and MOEMS.
Some aspects of using the A2BX4 crystals in digital recording are discussed. Special attention is paid to the temperature dependence of birefringence and absorption coefficient.
In the paper we presented numerical studies of gradient index optical splitters made in a multimode interference technology by K+«Na+ ion exchange process. The influence of geometrical parameters of multimode interference structure and technological process parameters is examined in numerical simulations and gradient index optical waveguide splitters are proposed for photonic applications.