Anna Pakula

In Situ Interferometric Monitoring of Fiber Insertion in Fiber Connector Components

We present an interferometric setup for in situ monitoring of fiber tip positions when inserting optical fibers for fixation in fiber connector components. It ensures an accurate fiber tip position at the fiber connectors front facet and across the fiber array in cases where postinsertion polishing is not possible. We demonstrate our technique by populating a plastic fiber connector for optical interconnect applications, and compare the fiber tip position measured in situ using our setup with the position measured off-line using a commercial white light interferometer, showing a deviation smaller than 5%.

Low-coherence interferometry with polynomial interpolation on Compute Unified Device Architecture-enabled graphics processing units

Abstract. An algorithm for interpolation of central fringe position in low-coherence interferometry measurements is presented. The algorithm is based on a polynomial curve fitting. Fast calculation of interpolation is possible due to the use of an NVIDIA Compute Unified Device Architecture (CUDA) technology, which allows independent analysis of different points of a high-resolution detector matrix on separate cores of a graphics processing unit (GPU). The dependency of the method’s accuracy on the spectral width of the light source is checked. The computation times on a GPU are compared with those achieved with a multicore central processing unit, showing nearly 30 times faster calculations when using CUDA technology. The algorithm accuracy is tested by measuring a flat glass surface with two different cameras—an ordinary CCD camera and a cooled EMCCD camera. Finally, the algorithm is applied to measurements of a populated optical fiber connector array prototyped using deep proton writing technology.

Measurements of characteristic parameters of extremely small cogged wheels with low module by means of low-coherence interferometry

This paper presents novel application of Low Coherence Interferometry (LCI) in measurements of characteristic parameters as circular pitch, foot diameter, heads diameter, in extremely small cogged wheels (cogged wheel diameter lower than θ=3 mm and module m = 0.15) produced from metal and ceramics. The most interesting issue concerning small diameter cogged wheels occurs during their production. The characteristic parameters of the wheel depend strongly on the manufacturing process and while inspecting small diameter wheels the shrinkage during the cast varies with the slight change of fabrication process. In the paper the LCI interferometric Twyman - Green setup with pigtailed high power light emitting diode, for cogged wheels measurement, is described. Due to its relatively big field of view the whole wheel can be examined in one measurement, without the necessity of numerical stitching. For purposes of small cogged wheels characteristic parameters measurement the special binarization algorithm was developed and successfully applied. At the end the results of measurement of heads and foot diameters of two cogged wheels obtained by proposed LCI setup are presented and compared with the results obtained by the commercial optical profiler. The results of examination of injection moulds used for fabrication of measured cogged wheels are also presented. Additionally, the value of cogged wheels shrinkage is calculated as a conclusion for obtained results. Proposed method is suitable for complex measurements of small diameter cogged wheels with low module especially when there are no measurements standards for such objects.

Source spectrum shaping method for low-coherence interferometry.

Low-coherence interferometry (LCI) suffers mainly from low signal-to-noise (S/N) ratio. By using the source spectrum shaping method (SSSM), the authors can enhance the visibility of the zero-order fringe (V) and S/N ratio in LCI. The presented approach was analyzed numerically for a set of theoretical Gaussian light sources, with different central wavelengths and different spectrum widths. The results have shown a significant improvement of the visibility V. Additionally, a set of commercially available light emitting diodes was analyzed to find the best possible setup. Results of numerical calculations were verified experimentally in an SSSM low coherence Twyman-Green interferometric setup equipped with three light sources.

Multi-wavelength interferometer for high accuracy measurement of long gauge blocks

In the paper the multiwavelength interferometer with automatic data analysis based on phase fraction method is described. It is used to extend measurement range without losing sensitivity, especially to calibrate long gauge blocks. Numerical simulations and experimental work results have been shown to confirm proper functioning of this method. However, stabilization of environmental conditions and light sources has significant influence on correctness of measurement results. To match those requirements measurement system, which will be built for Polish Central Office of Measures, has been designed. This design is based on Twyman-Green interferometer and assumes usage of two highly stabilized laser sources. Optical and mechanical design of this system has been shown. Moreover, system for monitoring and stabilization of environmental conditions is required.

VIS-NIR Full-Field Low Coherence Interferometer for Surface Layers Non-destructive Testing and Defects Detection

Low coherence interferometry (LCI) is a well known measurement technique that allows shape measurements with a nanometer resolution. The range of LCI is theoretically unlimited but in practice it is determined by the length of a scanning motion along the measurement axis. The resolution of the measurement is determined by the scanning resolution, the spectral characteristics of the light source and the fringe analysis algorithm.

Simultaneous shape measurement and layers detection by means of low coherence interferometry and optical coherence tomography

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

Interferometric method for in-situ monitoring of fiber insertion in 2D fiber connectors fabricated through Deep Proton Writing

Deep Proton Writing (DPW) is a rapid prototyping technology allowing for the fabrication of micro-optical and micro-mechanical components in PMMA, which are compatible with low-cost replication technologies. Using DPW, a high-precision 2D fiber connector featuring conically-shaped micro-holes for easy fiber insertion, was realized. When populating these fiber connectors by fiber insertion and fixation, a critical issue is the accurate control of the fiber protrusion. The use of laser interferometry to measure the fibers facet position with respect to the connector surface to within a few micrometers, is inconvenient in view of the measurement range as compared to the fiber dimensions. In this paper, we propose an interferometric method for in-situ monitoring of the fiber insertion depth, based on the phenomenon of low temporal coherence light interference in a Twyman - Green setup. In addition, achieving a few micrometers measurement range with low coherence light requires vertical scanning of the sample under test. The design of the experimental setup and the achieved measurement results are shown and discussed.

Combined optical coherence tomography and spectral technique for detection of changes in eggshells caused by Mycoplasma synoviae

Mycoplasma synoviae (MS) infection in poultry is a serious global epidemiological and economic problem. Usually, MS pathogen is responsible for respiratory disease, infectious synovitis and the eggshell apex abnormalities (EAA). The EAA may lead to an increase in the incidence of cracks and breaks of eggshells which often are reason of microbial infections and higher water vapor loss during the entire incubation process. All these problems can cause higher embryonic mortality and lead to significant economic losses. Most of eggs with EEA posses characteristic deformation of an eggshell, however, a number of those eggs infected by MS may be omitted during visual inspection. To prevent such situation a combined Full-Field OCT (FF OCT) and spectral technique for detection of MS infected pieces is proposed. After a numerical processing from a recorded transmittance spectra of a eggshell a few parameters are calculated. Those parameters describe the shape of the transmittance spectrum understood for example as the directional coefficient of a line matched to a graph, or maximum amplitudes of changes in a specified range of wavelengths. Analyses of those parameters allow shells assignment into one of two groups – eggs coming from healthy and MS infected poultry. Data obtained from FF OCT allow more precise evaluation of MS influence on the eggshell, for example changes in the micropores, which are responsible for proper embryo – environment gas exchange [1]. Authors present a new approach to food quality testing which in near future may be applied to reduce the egg production losses caused by MS in the commercial poultry industry.

Simple optical method for recognizing physical parameters of graphene nanoplatelets materials

Graphene nanoplatelets exhibit high potential for current engineering applications, particularly in context of conductive inks for organic and flexible electronic. Electrodes for organic displays are expected to be transparent in the visible part of electromagnetic spectrum. Thus this study aimed at full-field transmission measurements in the visible wavelength range. The paper presents transmission characteristics of different graphene samples. Samples, prepared using spray coating methods contained 3 types of deposited inks. Each of them was based on different concentration and size of graphene nanoplatelets. Moreover, they had various numbers of layers. Such materials were characterized by different parameters, like distribution of deposited carbon nanoparticles which is influencing layers homogeneity, resulting in different optical properties. Further, this research tries to establish a robust indicators characterizing examined samples. Authors built in Institute novel scanning optical system with fiber-based, compact spectrometer instead of other expensive techniques used for material characteristic in nanosciences i.e. high-resolution scanning electron microscopy. An optical scheme, design of system and technical parameters are described. Performed examinations show, that number of parameters derived from our measurements, strongly correlate with physical properties of deposited inks. Authors estimated surface roughness, homogeneity and distribution of nanoparticles agglomerates within the deposited layers. Presented results suggest, that this novel cost-effective, simple optical method of materials characterization especially in production of graphene nanoplates coatings can be promising in concern of repeatability assessment and optical properties.