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Proceedings Paper

Absolutely referenced distance measurement by combination of time-of-flight and digital holographic methods
Author(s): Markus Fratz; Claudius Weimann; Harald Wölfelschneider; Christian Koos; Heinrich Höfler
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Paper Abstract

We present a novel optical system for distance measurement based on the combination of optical time-of-flight metrology and digital holography. In addition absolute calibration of the measurement results is performed by a sideband modulation technique. For the time-of-flight technique a diode laser (1470 nm) is modulated sinusoidally (128 MHz). The light reflected and scattered by an object is detected by an avalanche-photo-diode. The phase difference between the sent and detected modulation is a measure for the distance between the sensor and the object. This allows for distance measurements up to 1.17 m with resolutions of ~2 mm. The interferometric setup uses 4 whispering-gallery-mode lasers to perform multiwavelengths-holographic distance measurements. The four wavelengths span the range from 1547 nm to 1554 nm. The unambiguous measurement measurement-range of the interferometric setup is approx. 7 mm while resolutions of 0.6 μm are observed. Both setups are integrated into one setup and perform measurements synchronously. Exact knowledge of the frequency differences of hundreds of GHz between the four lasers is crucial for the interferometric fine scale measurement. For this aim the light of the lasers is phase-modulated with frequencies of 36 GHz and 40 GHz to produce optical sidebands of higher order, thus generating beat signals in the hundreds-of-MHz regime, which can be measured electronically. The setup shows a way to measure distances in the meter range with sub-micron resolution.

Paper Details

Date Published: 4 April 2014
PDF: 10 pages
Proc. SPIE 8992, Photonic Instrumentation Engineering, 89920O (4 April 2014); doi: 10.1117/12.2039426
Show Author Affiliations
Markus Fratz, Fraunhofer-Institut für Physikalische Messtechnik (Germany)
Claudius Weimann, Karlsruher Institut für Technologie (Germany)
Harald Wölfelschneider, Fraunhofer-Institut für Physikalische Messtechnik (Germany)
Christian Koos, Karlsruher Institut für Technologie (Germany)
Heinrich Höfler, Fraunhofer-Institut für Physikalische Messtechnik (Germany)


Published in SPIE Proceedings Vol. 8992:
Photonic Instrumentation Engineering
Yakov G. Soskind; Craig Olson, Editor(s)

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