Karl Henrik Haugholt

Non-contact transflectance near infrared imaging for representative on-line sampling of dried salted coalfish (bacalao)

This paper describes a multi-spectral imaging near infrared (NIR) transflectance system developed for on-line determination of crude chemical composition of highly heterogeneous foods and other bio-materials. The system was evaluated for moisture determination in 70 dried salted coalfish (bacalao), an extremely heterogeneous product. A spectral image cube was obtained for each fish and different sub-sampling approaches for spectral extraction and partial least squares calibration were evaluated. The best prediction models obtained correlation R2 values around 0.92 and root mean square error of cross-validation of 0.70%, which is much more accurate than todays traditional manual grading. The combination of non-contact NIR transflectance measurements with spectral imaging allows rather deep penetrating optical sampling as well as large flexibility in spatial sampling patterns and calibration approaches. The technique works well for moisture determination in heterogeneous foods and should, in principle, work for other NIR absorbing compounds such as fat and protein. A part of this study compares the principles of reflectance, contact transflectance and non-contact transflectance with regard to water determination in a set of 20 well-defined dried salted cod samples. Transflectance and non-contact transflectance performed equally well and were superior to reflectance measurements, since the measured light penetrated deeper into the sample.

Optical, mechanical and electro-optical design of an interferometric test station for massive parallel inspection of MEMS and MOEMS

The paper presents the optical, mechanical, and electro-optical design of an interferometric inspection system for massive parallel inspection of MicroElectroMechanicalSystems (MEMS) and MicroOptoElectroMechanicalSystems (MOEMS). The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under test. The probing wafer is exchangeable and contains a micro-optical interferometer array. A low coherent and a laser interferometer array are developed. Two preliminary interferometer designs are presented; a low coherent interferometer array based on a Mirau configuration and a laser interferometer array based on a Twyman-Green configuration. The optical design focuses on the illumination and imaging concept for the interferometer array. The mechanical design concentrates on the scanning system and the integration in a standard test station for micro-fabrication. Models of single channel low coherence and laser interferometers and preliminary measurement results are presented. The smart-pixel approach for massive parallel electro-optical detection and data reduction is discussed.

Design of a micro-optical low coherent interferometer array for the characterisation of MEMS and MOEMS

The EU-project SMARTIEHS (SMART InspEction system for High Speed and multi-functional testing of MEMS and MOEMS) develops a new inspection concept for MEMS and MOEMS (M(O)EMS) testing at the wafer level [1]. The inspection systems on the market today are based on a serial approach inspecting one M(O)EMS structure at the time. In SMARTIEHS a parallel wafer-to-wafer inspection concept is adopted from the electronic probing cards in the micro electronics industry. A microoptical probing wafer is aligned with the M(O)EMS wafer under test. The 4-inch probing wafer contains a 5x5 array of micro-optical low coherent interferometers, inspecting shape and deformations of 25 M(O)EMS structures within one measurement cycle. The measurement time can thus be reduced by a factor of 25, scaling with the no. of interferometers on the probing wafer. A 5x5 channel smart pixel camera array detects and demodulates the interference signals [2]. The design of the micro-optical low coherent interferometer array is presented. The configuration of the array elements is based on a Mirau interferometer. The main challenge is to use standard micro-fabrication processes to produce the micro optical interferometer array.

Parallel approach to MEMS and micro-optics interferometric testing

The paper presents the novel approach to an interferometric, quantitative, massive parallel inspection of MicroElectroMechanicalSystems (MEMS), MicroOptoElectroMechanical Systems (MOEMS) and microoptics arrays. The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under test. The probing wafer is exchangeable and contains one of the micro-optical interferometer arrays based on: (1) a low coherent interferometer array based on a Mirau configuration or (2) a laser interferometer array based on a Twyman-Green configuration. The optical, mechanical, and electro-optical design of the system and data analysis concept based on this approach is presented. The interferometer arrays are developed and integrated at a standard test station for micro-fabrication together with the illumination and imaging modules and special mechanics which includes scanning and electrostatic excitation systems. The smart-pixel approach is applied for massive parallel electro-optical detection and data reduction. The first results of functional tests of the system are presented. The concept is discussed in reference to the future M(O)EMS and microoptics manufacturers needs and requirements.

An interferometric test station for massive parallel inspection of MEMS and MOEMS

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

UTOFIA: an underwater time-of-flight image acquisition system

In this article the development of a newly designed Time-of-Flight (ToF) image sensor for underwater applications is described. The sensor is developed as part of the project UTOFIA (underwater time-of-flight image acquisition) funded by the EU within the Horizon 2020 framework. This project aims to develop a camera based on range gating that extends the visible range compared to conventional cameras by a factor of 2 to 3 and delivers real-time range information by means of a 3D video stream. The principle of underwater range gating as well as the concept of the image sensor are presented. Based on measurements on a test image sensor a pixel structure that suits best to the requirements has been selected. Within an extensive characterization underwater the capability of distance measurements in turbid environments is demonstrated.

Low cost “laserless” FTIR spectrometer on the farm for real-time nitrous oxide soil emission measurements

A low-cost Fourier transform infrared (FTIR) instrument was developed where the traditional He-Ne reference laser was replaced by a low-cost linear encoder. An RMS sampling error of less than 20 nm was achieved by oversampling both the interferogram and the encoder signal and then resampling the interferogram using a correction table for the encoder. A gas calibration model was developed for the system, which was chosen to have a stroke length of 21 mm and, thereby, a resolution of 0.4 cm(-1) after apodization. The instrument was mounted on a vehicle and employed in an agricultural field test for measuring soil emissions, in particular nitrous oxide (N(2)O). The concentration of N(2)O was measured with a root mean squared error of 6 ppb. The results compared well with lab-based gas chromatography measurements.

Low Cost “Laserless” FTIR Spectrometer with Resolution Better Than 0.5 cm-1

We have designed a FTIR instrument where the traditional He-Ne reference laser is replaced by a low-cost linear encoder. We achieve an RMS sampling error of less than 50nm by oversampling both the interferogram and the encoder signal and then resampling the interferogram using a correction table for the encoder.