A distance meter has been developed using a pulse train emitted from a laser diode. The frequency spectrum of the pulse train consists of the fundamental frequency and its harmonics of the modulation current supplied to the laser diode. The interference effect between the detected signal and the field leakage, induced by the modulation current, was removed through the heterodyne detection of the second harmonic, and the systematic error caused from this interference effect was decreased in phase measurements. The precision of the distance measurement was improved, especially when the detected light signal was very weak.
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Seta et al. (1987) studied this question.
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