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Optical Profilometry and Vibration Amplitude Measurement with Multicore Fibers

Optical Profilometry and Vibration Amplitude Measurement with Multicore Fibers. M. Naci Inci. Physics Department , Bogazici University. Layout. Fourier Transform Profilometry (FTP) Vibration Amplitude Study with FT Analysis. Optical Profilometry.

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Optical Profilometry and Vibration Amplitude Measurement with Multicore Fibers

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  1. Optical Profilometry and Vibration Amplitude Measurement with Multicore Fibers M. Naci Inci Physics Department,Bogazici University

  2. Layout • Fourier Transform Profilometry (FTP) • Vibration Amplitude Study with FT Analysis

  3. Optical Profilometry • It employes the wave nature of light to determine shape and dimensions of objects. It uses structured light patterns that are generated through optical interference.

  4. A structured light pattern based on a two-beam optical interference

  5. Advantageous of the Optical Profilometry • Applicable in real-time • Non-invasive • Applicable to large areas • Hight resolution and high sensitivity • Computer compatibility

  6. Applications • Industrial otomation • Robotic vison • Quality control • Biomedical applications • CAD/CAM modelling

  7. Optical Profilometry: It is a measurement method based on the wave nature of light, which uses optical interference fringes of the laser beam

  8. Beam I Beam II  (A double-slit Young experiment) How do we obtain a structured light pattern?

  9. fiber fiber screen

  10. Why Fourier Transform Profilometry (FTP)? • FTP’s main advantage is that it uses only a single image to extract profile of an object. In other techniques, 3 or 4 images are required.

  11. Aim:To obtain a direct relationship between the object’s surface topography (z(x,y)) and the phase () of the structured light pattern Methodology:

  12. Two-beam interference fringe pattern analysis • Light intensity distributionover the surface in concern is • For the Fourier fringe analysis, Eq.1 can be written as • The FT of I(x,y) at the CCD camera is (1) (2) (3)

  13. A C C* u0

  14. A C* C u0 Fringe analysis • C (or C*) is isolated and then translated to the origin by u0 amount. • A(u, v)andC*(u+u0, v)are eliminated by bandpassfiltres • Inverse of FT is applied to determine the complex fn.c(x,y) • Phase of the structured light pattern is determined as • Phase-unwrapping is applied to correct 2π phase jumps • Surface topography and phase of the fringes are related as

  15. n1 n2 > Optical fiber n2 n1 Claddig Core

  16. Interference with two fibers

  17. Interference with four fibers

  18. Mutual coherence is required between fibre ams to obtain interference pattern Single source with a 2x2 fiber coupler Fibre arms are difficuilt to aline properly. Vibration, temperature, polarization, etc. result in a poor fringe visibility

  19. Alignment is even more difficuilt with 4 fibers

  20. Interferece with a two-core optical fibre 125 m

  21. Interferece with a four-core optical fibre

  22. Four-core fiber Manufactured by Hesfibel, Kayseri, Turkey (www.hesfibel.com)

  23. FT of I(x,y)

  24. FFT of the light pattern

  25. Phase Surface and phase are related as

  26. Experimental Setup

  27. (a) Triangular shape object; (b) projected fringepattern; (c) reconstructed surface of the object

  28. (a)Sculptured head object and the outlined area shows the analysed surface; (b) projected fringe pattern; (c)reconstructed surface of the object

  29. (a) An object made from sand and the outlined area shows the analysed surface; (b) projected fringe pattern; (c)reconstructed surface of the object

  30. (a)Projected fringe pattern of a flat plate with a 2 mm step. The area in the upper right-hand corner is 2mm higher than the rest of the plate; (b) 2D Fourier spectra of the analyzed pattern (c) Reconstructed surface K Bulut, MN Inci, Optics & Laser Technology (in press)

  31. A board marker K Bulut, MN Inci, Optics & Laser Technology (in press)

  32. Comparison between a cross section of the reconstructed surface with a circle of radius 14.4 mm. The RMS error is 0.4 mm.

  33. Vibration Amplitude Measurements

  34. If the object vibrates sinusoidal with an angular frequency , then the out-of-plane displacement of the object surface at (x, y) is given by A V(x, y): local amplitude of vibration B

  35. Since the frame rate of the CCD camera is much lower than the vibration angular frequency ω, the light pattern captured is proportional to the time average of I(x, y ,t) over one period:

  36. C and D are processed to obtain Vibration amplitude is obtained from

  37. 4 different vibration amplitudes studied ST Yilmaz, U Ozugurel, K Bulut, MN Inci, Optics Communications (to be published)

  38. Conclusion Multicore fiber based optical profilometry and vibration amplitude measuremets are promising. However, a larger fiber core seperation will improve the resolution of the optical method Acknowledgement Karahan Bulut, Tunç Yılmaz, Umut Özuğurel

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