Abstract
A heterodyne photodetection method is proposed in order to improve the signal to noise ratio of a frequency-modulated-continuous-wave- (FMCW-) like laser range finder. For this purpose, the non-linearity of the current–voltage characteristic of an avalanche photodiode (APD) is used. The photoelectric current is mixed with a local oscillator (LO) signal inside the APD working as an optoelectronic mixer. The signal from the LO can be injected inside the APD by an optical or an electrical channel, both techniques being compared in this paper. A model of the APD taking into account the thermal effects is then proposed. It is demonstrated that the conversion efficiency of the optoelectronic mixer reaches 0.5 in quasi-darkness conditions. Experimental results are in agreement with the theoretical analysis. The feasibility of an FMCW laser range finder using an APD as an optoelectronic mixer is then shown.
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