Adam Waz

WDM optocommunication technology used for multipoint fibre vibrometry

The multichannel WDM (Wavelength Division Multiplexing) technique inspired the concept of vibration measurements for many points of a vibrating object. The N-independent WDM separated 15XX nm fibre coupled laser diodes (used for optical fibre telecommunication) form coherent system of sources for multipoint measurement of vibrations according to the rule one wavelength - one point. The scattered light from the object coupled into the fibre, filtered coherently, after special signal processing, allows analysing amplitudes and phases of many vibrating points in real time. Some experiments and results of such system will be demonstrated.

Laser-fiber vibrometry/velocimetry using telecommunication devices

We presented the next step of our research connected with development of the vibrometry/velocimetry based on fiber into free space radiation and heterodyne detection of scattered light. Some experimental configurations utilizing erbium doped fiber amplifier (EDFA) are presented. We propose two solutions of optical interface between the fiber system and an object.

Intracavity polarization control in mode-locked Er-doped fibre lasers using liquid crystals

In this paper we present a novel configuration of an NPR mode-locked Er-doped laser. This new optical setup uses voltage controlled LC cells to replace standard retarders (quarter-and half-waveplates) inside the laser cavity. Using this novel, mechanical-adjustment-free setup a mode-locking was obtained with sub-500 fs pulse duration and an average power exceeding 40 mW. Presented results show that using simple LC cells, an optical layout of an NPR mode-locked laser can be greatly simplified.

Recent development of WDM fiber vibrometry

For the last few years we were elaborating the laser-fiber vibrometer working at 1550 nm. Our main stress was directed towards different aspects of research: analysis of scattered light, efficient photodetection, optimisation of the fiber-free space interfaces and signal processing. As a consequence we proposed the idea of a multichannel fiber vibrometer based on well developed telecommunication technique – Wavelength Division Multiplexing (WDM). We present the results of a just finished project “Developing novel laser-fiber monitoring technologies to prevent environmental hazards from vibrating objects” where we have constructed a 4-channel WDM laser-fiber vibrometer.

Demodulator electronics for laser vibrometry

One of the most important parts of a fiber-laser vibrometer is demodulation electronic section. The distortion, nonlinearity, offset and added noise of measured signal come from electronic circuits and they have direct influence on finale measuring results. Two main parameters of an investigated vibrating object: velocity V(t) and displacement s(t), influence of detected beat signals. They are: the Doppler frequency deviation f(t) and phase shift φ(t), respectively. Because of wide range of deviations it is difficult to use just one demodulator. That is the reason why we use three different types of demodulators. The first one is the IQ demodulator, which is the most sensitive one and its output is proportional to the displacement. Each IQ channel is sampled simultaneously by an analog to digital converter (ADC) integrated in a digital signal processor (DSP). The output signals from the two FM demodulators are proportional to the frequency deviation of heterodyne signals. They are sensitive directly to th...

Multichannel WDM vibrometry at 1550 nm

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

Laser-induced color marking of stainless steel

This paper presents the analysis of the impact of selected process parameters on the resulting laser color marking. The study was conducted for AISI 304 multipurpose stainless steel using a commercially available industrial fiber laser. It was determined how various process parameters, such as laser power, scanning speed of the laser beam, temperature of the material, location of the sample relative to the focal plane, affect the repeatability of the colors obtained. For objective assessment of color changes, an optical spectrometer and the CIE color difference parameter ΔEab * were used.

Three-stage all-in-fiber MOPA source operating at 1550 nm with 20W output power

In this work we present a high-power laser source developed in Master Oscillator Power Amplifier (MOPA) configuration. Presented MOPA source consists of three amplifying stages: pre-amplifier based on erbium-doped fiber, medium-power stage based on double-clad Er/Yb co-doped fiber and the power stage, based on Er/Yb co-doped doubleclad LMA fiber. Whole system is set up in All-In-Fiber technique, without any bulk, free-space optical elements. It provides over 20W of output power in the eye-safe 1550 nm band.

WDM Network for Multipoint Analysis of Scattered Laser Radiation

The multichannel WDM technique was the inspiration of the concept to measure vibration parameters from many points of a vibrating object (cars, planes, household equipment). The N-independent WDM/ITU separated 15XX nm fibre coupled laser diodes form coherent source system for multipoint measurement of vibrations according to the rule one wavelength- one point. The scattered light from the object coupled into fibre, filtered coherently, after special signal processing, allows analysing amplitudes and phases of many vibrating points in real time. Some primary experiments will be demonstrated

Application of a new four-channel vibrometer for determination of atherosclerosis: Further advances towards a handheld device

Cardiovascular diseases (CD) are the leading cause of death worldwide and their prevalence is expected to rise. Important in the etiology of CD is the stiffening of the large arteries (arteriosclerosis) and plaque formation (atherosclerosis) in the common carotid artery (CCA). Increasing evidence shows that both arteriosclerosis and atherosclerosis can be detected by assessing pulse wave velocity (PWV) in the CCA, and several techniques focus on the detection of PWV in this structure. In previous studies, laser Doppler vibrometry (LDV) was proposed as an approach to detect arterial stiffness. In the present work, a compact four-channel LDV system is introduced for PWV detection. Four phantom arteries were assessed mimicking real life cardiovascular pathologies. Due to the high sensitivity and the increased spatial and temporal resolution of the LDV system, PWV could be assessed, and even local changes in phantom architecture could be detected. The system could potentially be used to detect arteriosclerosis and arterial plaque during cardiovascular screening.