We report on the influence of intrinsic noise on the self-mixing signal associated with a vibrating target. The signal intensity of a semiconductor laser is investigated using a numerical simulation based on the rate equations incorporating Langevin noise forces. The photon density (signal intensity) as a function of the target displacement was calculated for the spontaneous emission factor β = 10{sup}-6 ～ 10{sup}-4. The reconstructed displacement waveform was obtained from the sawtooth signal caused by the self-mixing effect between the backscattered light from the target and the light in the laser diode. The influence of the noise on the displacement waveform of the vibrating target as a function of the feedback amplitude reflectivity r{sub}(ext) and the spontaneous emission factor β was shown. While the Langevin noise is greatly affect by β and the photon density was found to be more stable when β is less than 10{sup}-6, we found that the amplitudes of the reconstructed waveform with different β values are close to the true value of the target displacement amplitude (7.8 μm peak to peak) when r{sub}(ext) = 0.5% ～ 1.2%. The variation coefficient in the case of r{sub}(ext) = 0.5% ～ 1.2% remained below 7%. These results are potentially useful for precise displacement measurement.
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