Systematic distortions in electro-optical mixers

Electro-optical mixers (EOM) have tremendous potential for application in optical intensity-modulated time-of-flight distance measurement systems. Two different devices, Photonic Mixing Devices (PMD) and Metal-Semiconductor-Metal (MSM) are applied to distance measurement in this paper. The experimental results obtained show the presence of systematic distortions in the output signal of the device, resulting in measurement errors of up to a few centimeters. Careful analysis of the effects leads to the conclusion that illumination dependant non-linear effects take place inside local spots of the semiconductor. Consequently the introduction of a small diffusing plate for beam homogenization in front of the semiconductor drastically reduces the amount of systematic distortions. The distance measurement accuracy is doubled for PMDs, and even tripled for MSMs. Additionally the experimental data provides ties between charge injection mechanisms and the observed spurious signals.