Coherence dependence of fiber-optic laser Doppler velocimeter output using self-mixing laser diode

A new laser Doppler velocimeter (LDV) employing a self-mixing laser diode (SM-LD), which has a long optical fiber of 10 m to 1 km, as a light guide. This new LDV can measure a Doppler best signal with high signal to noise ratio in the range of 20-40 dB. The reason why the Doppler beat signal is obtained from a photodiode accommodated in the SM-LD having such a long fiber is attributed to the coherence length enhancement of the SM-LD, which extends to 400 m or more.<
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