# Silvano Donati

Silvano Donati is a scientist in photonics. He is an emeritus professor at the University of Pavia where he has been Full Professor for 30 years and created the Electro-Optical Engineering Group.

## Career

Donati started his career at CISE (a Research Center of the Electrical Generating Board) in 1966, initially with a 1-year CNR Scholarship, and from 1967 to 1975 hired full-time by CISE. There he carried out research on nuclear electronics and detectors, and on the nascent photonic instrumentation, notably telemeters, interferometers, and speckle pattern vibration sensors. Meanwhile, from 1967 to 1971 he was a teacher of the course in "Electronics" at ISTIM, the Master on mechanical engineering.
In 1971 he was appointed a lecturer at the University of Pavia for the recently-created 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.
In 1975 he become "Professore Stabilizzato", or tenured, moved full-time to the University of Pavia and started teaching his newly activated courses of "Electronic Materials and Technologies" and "Electro-Optical Systems", this last being the first course in Photonics of Italian Universities. In 1981 he was appointed Full Professor at the University of Pavia, a position he held until 2010.
During the years, he gradually improved the lecture notes of courses he delivered to students up to the point of publishing two textbooks: "Photodetectors" 448 pages, first published by Prentice Hall 2000, with a 2nd ed. in 2021, and "ElectroOptical Instrumentation", 442 pages, first published 2004 by Prentice Hall, translated in Chinese (Guang Dien Yi Chi) in 2006 with a 2nd ed. in 2023. From 2010 to 2014 he continued to give courses as a Lecturer, and in 2015 he was awarded of the Emeritus Professorship.
He also developed activity and taught courses in several universities of Taiwan as a visiting professor: NTU (Taipei) in 2005, NSYSU (Kaohsiung) in 2007 to 2010, NCKU (Tainan) in 2012, NCHU (Taichung) in 2013–14, NTUT (Taipei) in 2015–17, again NTU (Taipei) 2018–20, and 2021–2022 NCHU (Taichung), and 2023- 2024 NTUST (Taipei).
He has been Distinguished Lecturer for the IEEE Photonics Society, and Travelling Lecturer for Optica and SPIE, totalizing 120 location lectures in the period 2010 -2020.

## Research work

Donati's main field of research has been Photonic Engineering. In the period 1975 to 1990 he worked on components and sensors, with innovative contributions to the development of fiber couplers (ending in a spin-off, Tel.Es company, active for 7 years and with a 24-people workforce, selling for a period the best 0.05-dB insertion loss fused couplers) and optical isolators (both free-space and all-fiber). For fiber sensors, in 1985 he developed in Pavia the first prototype of fiber gyroscope (sponsored by Elsag Genova and later taken over by GEM) and the fiber current sensor.
In 1978, on his first research carried out at University of Pavia, he proposed a new configuration of interferometry, he called "induced modulation", characterized by the absence of any optical component external to the source and based on the modulation of the cavity field produced by optical signal returning from the remote target. 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. Also, he employed as an optical stethoscope to measure heart beat and respiratory sounds. However, progress was slow because of the bulky HeNe source, until single-mode diode lasers, reliable and low cost, became finally available in the '90s. Then, a lot of researchers internationally started to develop the new interferometer, at that time dubbed "self-mixing" because of the in-cavity interaction. The big problems with the laser diode was that only a single channel is availabile (the AM), so that the measurement is affected by ambiguity. 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. Also, he and his Group developed novel methods of absolute distance measurement, angle measurement, echo detectors, and measurement of laser parameters, like linewidth and α−factor. In 2013 one of his collaborators has started a successful spin-off on SMI, the Julight company. Major papers on Self-Mixing Interferometry published by Donati and co-workers totals 60 and have collected 4,500+ citations.
Another achievement of Donati, also belonging to the class of coupling phenomena in laser sources and their applications, is chaos cryptography. In 1996, after a paper on the coupled-laser diode dynamics at high level showing the already known bifurcation, multiperiodicity and chaos, he and his colleague V.Annovazzi-Lodi developed chaos synchronization and proposed to make cryptography by chaos shift keying[9], a progress respect to the plain chaos masking of signals. A lot of work followed these seminal papers, fostering two rounds of EEC FET projects which involved seven international Groups headed by C.Mirasso of IMEDEA. 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.
A recent contribution of Donati to the improvement of those imaging device that include substantial circuits for the pixel by pixel processing, also known as smart pixels – like 3D telemeters – has been the idea of trading solid angle of acceptance for area increase, taking advantage of the invariance of radiance. So, SPAD arrays with low fill factor (e.g. FF=0.05) thanks to an array of micro-lenses can recover almost fully the FF loss. Microlens arrays are used nowadays extensively.

## Award and honors

* 1999 he received the Guglielmo Marconi Prize, awarded by AEI 1999.
* 2002 he received the elevation to "Fellow Member" from IEEE
* 2003 he received the elevation to Optica Fellow
* 2009 he received the "Distinguished Lecturer Award" from the IEEE Photonics Society
* 2009 he received the elevation to "Life Fellow Member" from IEEE
* 2011 he received the "Distinguished Service" Award of the IEEE Photonics Society
* 2015 he received the "IEEE PhoS "Aaron Kressel Award" for research in semiconductor lasers
* SPIE (permanent position)