Invention of the Self-Mixing Interferometry

Professor Donati first devised the scheme of self-mixing interferometry in 1977 (paper [17d]) with the demonstration of the fringe-counting interferometer based on a He-Ne laser source. A seminal paper [37d] followed in 1995 with the adaptation of the self-mixing scheme to the laser diode. To do that, he devised a new scheme capable of circumventing the sign (or direction) ambiguity of the interferometer, using just a single (amplitude) channel. Paper [37d] reporting theory and experiment has become in the years a must reading for all those starting in the field and has collected 150+ citations. Other 4-5 papers refining the subject followed in years 1997-2000 [47d, 60d, 63d, 66d], collecting additional 250 citations.

Nowadays, self-mixing scheme is recognized as a viable scientific tool in a variety of applications, ranging from detection of remote echoes [2a] to measurement of displacement, velocity, vibrations, and several physical quantities (return loss, optical insulation, coupling factor, attenuation, line-width, alpha factor, etc.).

About applications to consumer goods, Philips (NL) has used a self-mixing device as the scroll-down sensor of cellular phones and playstations. Our Lab at University of Pavia has developed and sold several preproduction units of: a Selmix Vibrometer and a Displacement Interferometer operating on a normal diffusing surface by means of BST (Bright Speckle Tracking) technique [63d], that is, without the need of a corner cube retroreflector.

Invention of Optical CSK (chaotic-shift-keying)

Another application of coupled oscillators actively pursued by Professor Donati has been the optical chaos generated by mutual and cross coupling. He started with the study of weak-coupling modulation [22d] and then extended the theory to the treatment of strong mutual coupling and self-coupling [36d]. The first discovery [36d] was that a state of final synchronization follows the chaos regime, the second and most important was the conception of CSK (chaotic-shift-keying) scheme first proposed in 1997 [49d] and nowadays widely used in chaotic-coded communication systems. Last, paper [55d] provided new insight on the regimes of injection and locking, another work widely referenced. In total, the seminal papers on the chaotic regime and applications have totalled 300+ citations.

Two EC FET programs (Occul, Picasso) have been triggered by this research, pooling seven partners from I, F, D, E, UK, GR. The cooperation resulted recently in a Letter to “Nature“ reporting the first experimental results.

Worth to mention, “Coupling Phenomena and applications to Selfmix and Chao” have been the subject of a Distinguished Lecturer award by the IEEE LEOS Society to prof.Donati, for the year 2007/08 and 2008/09, when he visited 20 LEOS Chapters around the globe.

New Theory of Optical Amplifier Noise

This theory shines new light on the origin of noise in optical amplifiers. A totally new approach was introduced in [48d], demonstrating that the noise at the output of any optical amplifier is just the amplified vacuum fluctuation, originating from the pumping input port (left open to the vacuum). The new model has been used to predict cascaded noise of optically regenerated fiber trunks [57d].

The main theory, including analytical development and figures are reprinted in Agrawal’s book “Applications of Nonlinear Fiber Optics”, and excerpted in detail by Desurvire’s book “Optical Amplifiers – 2^nd edition”

Major Contributions to ElectroOptical Instrumentation

These contributions range widely, from telemeters [10d, 11e] and LLLTV and vision through turbid media [4d, 5d, 12d, 13d] to optical gyroscopes [32e, 50d, 56d, 67d, 2c] to magneto-optical sensors [26d, 27d, 35d, 14e, 36e], as well as conventional and self-mixing interferometers, also in presence of speckle pattern [20d].

They are summarized by the book “Electro Optical Instrumentation”, published by Prentice Hall in 2004 and later translated in Chinese by Shanghai University Press (2006), made of an India edition (2006) and also available as e-book (2008).

Major Contributions to Photodetector Noise Theory

The main achievement are: the theory of photomultiplier gain and noise, established in 1970 [1-3d, 1c] and still today unsurpassed, the theory of the avalanche photodiode [3d], the analysis and experiments about the measurements of correlation [9d] and of squeezed-state radiation [33d, 20b]. Most recently, the new model of the noise in photodetection [2a] has been developed, which is accurate at the level of the second quantization of the electromagnetic field. All the original results have been incorporated in the book “Photodetectors”, published with Prentice Hall in 1999.

Major Contributions to All-Fiber Components and Sensors

In this field, the Author has given innovative contributions to: magneto-optical components (isolators and circulators) [25d, 13b, 41d, 39d] piezo-actuators on silica [54d], fiber-tip components [51d, 42d] and last but not least, fiberoptic couplers [36d, 31d, 73e].

The exceptionally good performances achieved with fused couplers (notably a 0.01 dB loss versus the 0.5 commonly offered by vendors as the best) has prompted a spin-off pursued by a young graduate of our University, who was able to set-up a 24-people spin-off Company (TELES, Milano) producing a 7 M$ year sales in the period 1995-2002.

Publications of the ElectroOptic Group leaded by prof. Donati, grouped by topic are: INTERFEROMETRY - NOISE in DEVICES and SYSTEMS – OPTICAL and FIBEROPTIC SENSORS - SEMICONDUCTOR LASERS - OPTICAL CHAOS - OPTICAL AMPLIFIERS – FIBEROPTIC COMPONENTS

The list witnesses the growth of the Optoelectronic Group, in scientific strength and breath of reach, a constant concern for professor Donati’s mentorship of his Group.

Most papers can be downloaded at the Author’s website http://www-3.unipv.it/dona

and the graduate students

ti