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Proceedings Paper

Speckle noise reduction of a dual-frequency laser Doppler velocimeter based on an optically injected semiconductor laser
Author(s): Chih-Hao Cheng; Jia-Wei Lee; Tze-Wei Lin; Fan-Yi Lin
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Paper Abstract

We develop and investigate a dual-frequency Laser Doppler Velocimeter (DF-LDV) based on an optically injected semiconductor laser. By operating the laser in a period-one oscillation (P1) state, the laser can emit light with two coherent frequency components separated by about 11.25 GHz. Through optical heterodyning, the velocity of the target can be determined from the Doppler shift of the beat signal of the dual-frequency light. While the DF-LDV has the same advantages of good directionality and high intensity as in the conventional singlefrequency LDV (SF-LDV), having an effective wavelength in the range of microwave in the beat signal greatly reduces the speckle noise caused by the random phase modulation from the rough surface of the moving target. To demonstrate the speckle noise reduction, the Doppler shifted signals from a moving target covered by the plain paper are measured both from the SF-LDV and the DF-LDV. The target is rotated to provide a transverse velocity, where the speckle noise increases as the transverse velocity increases. The bandwidth of the Doppler signal obtained from the SF-LDV is increased from 4.7 kHz to 9.4 kHz as the transverse velocity increases from 0 m/s to 5 m/s. In contrast, the bandwidth obtained from the DF-LDV maintains at 0.09 Hz with or without the rotation limited by the linewidth of the P1 state used. By phase-locking the laser with a RF current modulation, the linewidth of the P1 state can be much reduced to further improve the velocity resolution and extend the detection range.

Paper Details

Date Published: 28 February 2012
PDF: 6 pages
Proc. SPIE 8255, Physics and Simulation of Optoelectronic Devices XX, 82551P (28 February 2012); doi: 10.1117/12.907359
Show Author Affiliations
Chih-Hao Cheng, National Tsing Hua Univ. (Taiwan)
Jia-Wei Lee, National Tsing Hua Univ. (Taiwan)
Tze-Wei Lin, National Tsing Hua Univ. (Taiwan)
Fan-Yi Lin, National Tsing Hua Univ. (Taiwan)

Published in SPIE Proceedings Vol. 8255:
Physics and Simulation of Optoelectronic Devices XX
Bernd Witzigmann; Marek Osinski; Fritz Henneberger; Yasuhiko Arakawa, Editor(s)

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