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Proceedings Paper

Distance Measurements using a Laser Diode and by Heterodyne Detection with an Avalanche Photodiode
Author(s): Katuo Seta; Tadanao Oh'ishi
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Paper Abstract

A high resolution distance meter was built using a laser diode(LD) and an avalanche photodiode(APD). The laser diode LD was modulated directly by an RF current whose frequency f1 is 300 - 500 MHz, in order to obtain high resolution. The modulated light beam emitted from LD was sent to the target, returned, and detected by APD. The heterodyne detection was done in APD without any mixer in the RF region to measure the phase shift in the low frequency region. In APD, another RF current whose frequency f2 is f1 + δf was supplied together with an ordinary DC bias. The beat signal δf of these two RF signals was generated by modulating the amplification of APD. The phase shift between this beat signal and the reference signal of frequency Of was measured. The distance between the apparatus and the target was calculated from the phase shift, the modulation frequency of LD and the time delay in the apparatus. Although the phase shift was measured in the low frequency region, that is, the beat frequency region, a high resolution of about 0.1 mm was obtained easily, because of the short modulated wave-length in the RF region. The heterodyne detection in APD brings us the following merit. First, the apparatus is simplified, since the output signal of APD can be handled without any particular consideration made for high frequency region, for example, the impeadance matching and so on. Second, a high sensitivity is obtained without any high performance mixer. It is possible to measure a distance even when the intensity of the reflected light is below 1 nW. It means that a distance up to about 10 - 20 m can be measured without any reflector, with high resolution.

Paper Details

Date Published: 20 April 1987
PDF: 6 pages
Proc. SPIE 0740, Laser Diode Optics, (20 April 1987); doi: 10.1117/12.939736
Show Author Affiliations
Katuo Seta, National Research Laboratory of Metrology (Japan)
Tadanao Oh'ishi, National Research Laboratory of Metrology (Japan)

Published in SPIE Proceedings Vol. 0740:
Laser Diode Optics
David W. Kuntz, Editor(s)

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