An appropriate setting of the OTDR can help to improve the calibration reducing the uncertainty of measurements. We present some criterions for setting the Optical Time Domain Reflectometer (OTDR) for its distance scale calibration by means of a Recirculting Delay Line (RDL). The evaluation of some parameters such as location of the event, span of measurements, distance range and pulse width were carry out experimentally using a RDL calibrating system.
The principle purpose of this work is to providing some general analysis and interpretation in both theory and techniques concerning high accuracy of the thin metallic wire diameter measurement. The closest estimation of the magnitude requires understanding and analyzing the interaction between light and matter (wire). The wires diameter we re concern is between 30 to 500μm. The work is focus on both science and metrology. To reach this goal the simplicity and accuracy is required especially for an industrial automatic implementation control.
The article is organized as follow: the section one consist of analyzing and understanding of theoretical interpretation for laser diffraction by thin metallic wire. The second section contains analysis of the experimental set-ups used for calibration and measurement. The followed section is data analysis to estimate the angular location of the minima. With some conclusions we close to achieve the work.
The accuracy and precision of the thin wires still requiring special attention. Both theoretical and experimental studies together may give closest approximation to the "real" value. Concerning the optical technique of measurement, perhaps one may analyze more in detail the interaction between light and matter (wire) which can lead to a simple mathematical approach. Besides this, a calibrating system and robust technique of measurement is required both in the industrial sector and laboratories. Measuring the wires depends especially on how much accuracy and precision we want to achieve, we have static or dynamic measurement, which kind of wire we need to measure...etc. This report shows some work about the diffraction models and some measurement of the thin wire (30-500 μm). Statistical technique of measurement is provided as well.
The purpose of this paper is to improve the metallic wire diameter measurement. The size of some thin wires and slits has been achieved using the spectrogoniometer which represents good alternative system of detection. The fact that, the technique of measurement may be regarded as bringing more calibrated diameter. Since it provides wide range of detection, possibility to control the output signal readjusting a minimum of points per fringe and few image error to deal with comparing to other measurement techniques. The target-arm of detection rotated and drifted by a stepping motor of high resolution. As we know the diffraction of the thin wires using Fraunhofer technique is very suitable for an automatic control in the process of fabrication. Whereas, the more precise diameter we want the more deeper study is required (both theory and experiment). Concerning the physical approach of the phenomena, we fit our data to a polynomial of the third order. The error of each coefficient is given. The odd term presented in the polynomial function may be due to the deviations from the ideal properties of the components. Once the measurements are made, a special care of the experimental data is required in order to deduce the right diameter confining us only to the minima of the diffraction pattern. The wire diameter accuracy depends not only how good is our signal but as well how good our analysis of data.
The laser diffraction is a robust and precise technique to monitor wire diameters in-line. However, classical Fraunhofer diffraction formulas are not appropriate for 3-dimensional object size determination. The Babinet's principle allow to use such formulas only for angles of diffraction that tend to zero. A real diffraction measurement necessarily takes a finite angular range (approximately 10 degrees) and therefore, an error will be introduced if using classical formulas. The exact electromagnetic formulation is not appropriate to deal with 3-D objects, basically because it does not provide explicit formulas to determine the wire diameter. We have worked a pseudo-empirical approach out to reach simple accurate and reliable diffraction formulas that use exclusively the fringe pattern. To validate the diffraction formulas we need a calibration of the wire diameter. To accomplish this, we have introduced a hybrid set-up which allows interferometric and diffraction measurements over the same area of the wire. Using a He-Ne laser and a plus or minus 10 degree measurement range we observe, typically, a diameter overestimation of approximately 0.5 microns for different metallic wires (approximately 30 - 300 micrometer). From this work, we can also extract a practical physical insight to diffraction phenomena in terms of the Geometrical Theory of Diffraction (GTD). Many optical techniques for metrology of high resolution must take into account diffracted light.
The laser diffraction is a robust and precise technique to monitor wire diameters in-line. However, classical Fraunhofer diffraction formulas are not appropriate for 3D object size determination. The Babinet's principle allow to use such formulas only for angles of diffraction that tend to zero. A real diffraction measurement necessarily takes a finite angular range (approximately 10 degree(s)) and therefore, an error will be introduced if using classical formulas. The exact electromagnetic formulation is not appropriate to deal with 3D objects in a simple way. On the other hand we observed a systematic overestimation of the diameter, even very small angle of observation, in other words, a small misfit with the Babinet's principle.
KEYWORDS: Diffraction, Geometrical optics, Data modeling, Statistical modeling, Statistical analysis, Systems modeling, Error analysis, Optical engineering, Instrument modeling, Control systems
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.