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    National Tsing Hua University Institutional Repository > 電機資訊學院 > 電機工程學系 > 會議論文  >  Speckle noise reduction of a dual-frequency laser Doppler velocimeter based on an optically injected semiconductor laser


    Please use this identifier to cite or link to this item: http://nthur.lib.nthu.edu.tw/dspace/handle/987654321/83978


    Title: Speckle noise reduction of a dual-frequency laser Doppler velocimeter based on an optically injected semiconductor laser
    Authors: C. H. Cheng;J. W. Lee;T. W. Lin;F. Y. Lin
    教師: 林凡異
    Date: 2012
    Publisher: International Society for Optical Engineering
    Relation: SPIE Photonic West, San Francisco, USA, 24 - 26-January 2012
    Keywords: laser
    velocimeter
    semiconductor
    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.
    Relation Link: http://spie.org/
    URI: http://nthur.lib.nthu.edu.tw/dspace/handle/987654321/83978
    Appears in Collections:[電機工程學系] 會議論文
    [光電工程研究所] 會議論文

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