C. Tyszkiewicz

Impressing technology of optical Bragg's gratings on planar optical sol-gel waveguides

The aim of the presented investigations was to develop a technique of producing Bragg’s grating couplers on planar waveguides. Waveguides are obtained by means of the sol-gel technology. The introduction of a light beam into the structure of the waveguide is in the case of planar or strip optical systems always an essential technical problem, requiring simple and reproducible solutions without extending excessively the waveguide structure. The paper presents a technology of producing grating couplers by impressing the pattern of the network while forming the planar waveguide structure applying the sol-gel method. Some remarks concerning the sol-gel technology are also presented. The results of investigations on grating couplers obtained in such a way have been discussed, too.Attention has been drawn to the possibility of using such structures in optoelectronic sensors, particularly gas sensors, including sensors of water vapour as well as toxic gases.

Optical fiber sensors of magnetic field applying Faraday's effect

This work presents a system for magnetic field intensity measurements. The idea of measurements is based on an influence of external magnetic field on the polarization state of singlemode light propagating along optical fibers. In the paper some experimental results of testing investigations of the system for measurements magnetic field of high intensity are presented. The final aim of the investigation outlined below is to work out magnetic field intensity sensors which, together with optical fiber temperature sensors and electric field intensity sensors, will make possible, in the future, to monitor fully operation of electromagnetic power units such as, for example, high voltage power transformers.

Planar waveguide sensor of ammonia

The paper presents the concept of forming ammonia sensor based on a planar waveguide structure. It is an amplitude sensor produced on the basis of the multimode waveguide. The technological base for this kind of structure is the ion exchange method and the sol-gel method. The planar multimode waveguide of channel type is produced in glass substrate (soda-lime glass of Menzel-Glaser company) by the selective Ag+↔Na+ ion exchange. On the surface of the glass substrate a porous (~40%) silica layer is produced by the sol-gel method. This layer is sensitized to the presence of ammonia in the surrounding atmosphere by impregnation with Bromocresol Purple (BCP) dye. Therefore it constitutes a sensor layer. Spectrophotometric tests carried out showed about 50% reduction of cross-transmission changes of such sensor layer for a wave λ=593 nm caused by the presence of 25% ammonia water vapor in its ambience. The radiation source used in this type of sensor structure is a light emitting diode LED. The gradient channel waveguide is designed for frontal connection (optical glue) with a standard multimode telecommunications waveguide 62.5/125μm.

Sensor properties of the input grating couplers

This work presents results of the theoretical analysis as well as the results of experimental study on sensing structures with grating couplers. Grating couplers with a groove density of 1250g/mm were produced by us using the method of master grating embossing in a sol film. The waveguide films SiO2:TiO2 of high refractive index have been produced using the sol-gel method

Rib waveguides based on the sol-gel derived SiO2 :TiO2 films

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

Straight and bended high refractive index rib waveguides – theoretical analysis

This paper raises two questions concerning guiding properties of silica-titania rib waveguides. The first one is a relationship between silica-titania rib waveguides morphological parameters and their single mode operation regime. A set of these parameters includes rib height t, width w and a thickness h of a parent slab waveguide. It was shown that if a parent slab waveguide thickness is equal or higher to the value which maximizes homogeneous sensitivity of a fundamental TM mode then, depending on a value of rib width, there can be single or double range of rib height values for which the rib waveguide is single modal for quasi-TM modes. The second issue concerns an analysis of a magnitude of bend losses. It was shown that a magnitude of bend losses in silica-titania rib waveguides can be small enough allowing their application in designing of planar integrated optical circuits. The magnitude of bend losses is significantly decreased when slab waveguides adjacent the rib are cut-off.

Theoretical analysis of slab waveguides supporting SPP modes toward their sensitivity characteristics

This work is devoted to studying the dielectric/metal multilayer planar waveguide structure that is composed of a highrefractive index, single mode, silica-titania film deposited on a BK7 glass substrate. The waveguide film is loaded with a thin gold film, through a thin silica film. It is assumed that a semi-infinitive cover have the same refractive index as the water. There are presented and analyzed spectral characteristics of effective indexes of TM-polarized: dielectric and surface plasmon polariton (SPP) modes. Analysis of these characteristics is aimed at finding conditions for exciting the dielectric TM0 mode and two SPP modes: antisymmetric and symmetric. Assuming that excitation is done with a field distribution of the unloaded TM0 mode carried in this structure if the gold film is not present. The analysis is carried for the gold film having thicknesses dm=50 nm. It is shown, that conditions for matching effective indexes of the unloaded TM0 mode and SPP modes are met in a broad range of silica film thickness. The presence of the silica film is indispensable for reduction of a refractive index difference between loaded and unloaded TM0 modes. It is shown that a sensitivity of this structure toward a small change of the cover refractive index is inconsiderably dependent on silica film thickness for the antisymmetric SPP mode. On the contrary, a sensitivity of the symmetric SPP mode, whose refractive index undergoes a discontinuous change with respect to wavelength changes its sign in function of the buffer film thickness.

Design and characterization of composite planar polarimetric interferometer

This paper presents the design and theoretical characterization of a composite uniform-gradient planar waveguide polarimetric interferometer. Presented structure is composed of an Ag+↔Na+ ion-exchange based waveguide formed in Borosilicate 33 glass substrate and a uniform, sol-gel based, silica-titania film. Characteristics of homogeneous sensitivity difference for TE0-TM0, TE0-TE1 and TM0-TM1 modes in function of the uniform film refractive index and the gradient waveguide refractive index profile are given. Because thermal annealing is an inseparable part of the sol-gel process, the gradient index waveguide is subjected to a rediffusion process. The original refractive index profile is flattened. It was shown that a presence of the gradient waveguide increases sensitivity differences over values which can be obtained for single layer uniform silica-titania waveguides. Moreover, it was shown that a range of uniform film thickness values, for which sensitivity difference of the composite structure is maximized, is downshifted to a range which can be much easier obtained with a sol-gel process.

The waveguide structures of the inverted-rib type

This paper presents an analysis of the possibilities of producing waveguide structures of the inverted-rib type. Such structures can be produced on the basis of planar gradient strip waveguides (channel waveguides) produced in a glass substrate by the ion exchange method. The glass surface is then covered with a thin uniform optical layer with a high refractive index. The thickness of this layer is less than the cut off thickness for the used wavelength. The wave propagation is therefore possible in the gradient area only. The homogeneous sensitivity of such waveguides is much greater than in case of single-mode waveguides without a uniform layer. The paper presents the calculations of homogeneous sensitivity for single-mode waveguides of the rib type, the inverted rib waveguides and the gradient waveguides. The use of single-mode inverted rib waveguides in the design of the planar interferometer in the Young configuration was proposed.

Sensitive films based on porous sol-gel silica

The paper is devoted to the sensitive films for application in chemical sensors. These films, made of the sol-gel derived porous silica, were fabricated via a sol-gel dip-coating method. We have obtained silica layers of the minimum refractive index of ~ 1.22 and porosity ~47%. These layers were sensitized with a pH indocator - bromocresole purple. The indicator was introduced into porous silica layers by means of impregnation. Methods and results of characterization of porous silica films, before and after sensitization are presented in this paper. It was shown that films are very sensitive toward ammonia.