Design and experimental verification of a microscope-based circular-polarization interferometer developed for measuring the vibration of miniature specimens is detailed. This interferometer, which comes in either a two-detector or a four-detector configuration, demonstrates that the optimum operating point of a circular-polarization interferometer depends strongly on the signal detection and processing algorithms adopted. The influence of the specimen surface optical properties on the desired operating conditions is also examined. The optimum operating point of the two-detector configuration demands that the two returning light beams emitting from the specimen possess equal intensity, which matches the understanding of traditional interferometers, where two equal interference arms achieves the best interference efficiency. Surprisingly, it appears that the optimum intensity ratio for the four-detector configuration occurs if the two interference arms possess equal intensity before it hits the specimen. That is, under the constraint of a constant light source, it appears that the optimum operating point of a four-photodetector circular-polarization interferometer is independent of the surface optical properties. Both theoretical and experimental results that verify the interaction between the optoelectronic configuration and the signal-processing algorithms implemented are presented.