Real-Time Self-Mixing Interferometer for Long Distances

This paper describes a novel instrument based on a self-mixing optical interferometer, able to reconstruct the target speed and direction, without heterodyne detection. The real-time elaboration employs the signal nonlinearity to recover the speed sign in the frequency domain. The target speed is measured by the signal frequency, while the speed sign is evaluated by the phase of the harmonics in the frequency domain. The high-sensitivity of the elaboration allows the measurement over diffusive target with distances up to 10 m. The measurements results have been successfully compared with a very-high resolution commercial calibrated instrument.