Here he carried out researches on nuclear electronics and detectors, and on the nascent photonic instrumentation, notably telemeters, interferometers, and speckle pattern vibration sensors.
In 1971 he was appointed a lecturer at University of Pavia for the just started curriculum in Electronic Engineering, and there he set up and equipped the Laboratorio Circuiti for the circuit design teaching aided by hands-on experiments of assembling and testing, the first of the genre in Italy.
The modulations are both AM and FM, and these two signals carry the usual sinφ and cosφ of the conventional interferometers, φ= 2(2πL/λ) being the optical pathlength to the target at distance L and back.
In a seminal paper Donati demonstrated how to detect both AM and FM signals with a Zeeman-split HeNe laser, and from them how to measure the displacements either by counting λ/8 increments or by an analogue reconstruction of the L=L(t) waveform, with sub-λ accuracy.
In 1994, Donati and his Group proposed the moderate-feedback regime, by which the waveform cosφ is distorted by switching that carries the sign of the displacement, an idea patented in 1994 and since then used in all the applications that followed.
The activity of Donati continued in the years 2002-2015 with the application of the self-mixing interferometer (SMI) to a variety of measurement tasks, including vibrometry for sub-nm amplitude signals by means of a closed loop analysis - a new configuration opening the way to several applications, notably non-contact mechanical spectral analysis, mechanical hysteresis cycle measurement, and MEMS diagnostics.
As a result, a chaos-cryptography InP chip incorporating laser diode, modulator and attenuator, and serving as a transmitter and receiver of chaos-coded information, has been finally developed.