An Historical Survey on Light Technologies

Following the celebration of the International Year of Light and Light-based Technologies in 2015, this paper presents a survey of the exploitation of light throughout our history. Human beings started using light far into the Stone Age, in order to meet immediate needs, and widened its used when ancient civilizations developed. Other practical uses were conceived during the Middle Ages, some of which had a deep impact on social life. Nevertheless, it was after the Scientific Revolution and, to a wider extent, with the Industrial Revolution, that more devices were developed. The advancement of chemistry and electricity provided the ground and the tools for inventing a number of light-related devices, from photography to chemical and electrical lighting technologies. The deeper and broader scientific advancements of the twentieth century, throughout wave and quanta paradigms and the research on the interactions with matter at the sub-atomic level, have provided the knowledge for a much broader exploitation of light in several different fields, leading to the present technological domains of optoelectronics and photoelectronics, including cinema, image processing, lasers, photovoltaic cells, and optical discs. The recent success of fiber optics, white LEDs, and holography, evidence how vastly and deeply the interaction between light and man is still growing

Negative Feedback, Amplifiers, Governors, and More

The invention of the negative feedback amplifier by Harold S. Black (1898\u20131983) in 1928 is considered one of the great achievements in electronics and in fact it stands among the IEEE milestone, being credited to the Bell Labs. Black had been hired by Western Electric in 1921 and assigned to work on the Type C system, a newly introduced three-channel telephone network, whose push-pull vacuum-tube repeater amplifiers tended to produce a too large harmonic distortion when connected in tandem [1]. At that time, telephone network where in a great spread and the Bell Labs arose quickly as the major research company of the sector. The extension of lines over long distances required counteracting signal attenuation, which occurred, though at a reduced level, also in lines provided with Pupin\u2019s loading coils to match the Heaviside condition for distortion-free transmission

Seventy Years of Getting Transistorized

Vacuum tubes appeared at the break of the twentieth century giving birth to electronics. By the 1930s, they had become established as a mature technology, spreading into areas such as radio communications, long distance radiotelegraphy, radio broadcasting, telephone communication and switching, sound recording and playing, television, radar, and air navigation. During World War II, vacuum tubes were used in the first electronic computers, which were built in the United Kingdom and the United States. Although vacuum tubes had been a successful technology, they were also bulky, fragile and expensive, had a short life, and consumed a lot of power to heat the thermo-emitters. These drawbacks promoted the search for completely new devices. Alternative solutions had long been considered, but without significant developments

A Question of Coherence

open1noElectromagnetic waves were first postulated by James Clerk Maxwell (1831-1879) in 1865. To demonstrate their existence 22 years later, Heinrich Hertz (1857-1894) had to design new instrumentation that he used to carry out an experiment than had never been performed before. To detect the waves produced by his oscillating electric circuit, he used a very crude receiver, subsequently known as the Hertz resonator.openGuarnieri, MassimoGuarnieri, Massim

Trailblazers in Electromechanical Computing

Over the last six decades, electronic computing has spread so deeply in science and technology to became a fundamental tool for studying, researching and designing. Passing through vacuum tubes, transistors, integrated circuits and microprocessors, electronics has allows an amazing growth in computing power [1] and the recent commissioning in 2016 of the all-Chinese Sunway TaihuLight with a computing power 93 PFLOPS (1015 floating point operations per second), two and a half times larger than the previous world top supercomputer, the Chinese Tianhe-2 of 2013 powered with Intel processors, suggests that the evolution is still far from saturation. It is quite intriguing to wonder what was automatic computing before electronics started such a boost in computing power. Indeed, the search for mechanical tools aimed at relieving from the burden of computing goes far back into the past, at least to the ancient times when the abacus was built. However, it was with electricity that this possibility made a major step ahead

Solidifying Power Electronics [Historical]

More than one century ago, in 1902, American engineer Peter Cooper Hewitt (1861\u20131921) derived the mercury arc-rectifier, enclosed in a glass bulb, from his mercury-vapor lamp of the previous year. He devised its use for feeding dc motors from alternating currents. As the first rectifier for power uses (two years before Fleming\u2019s diode and four before De Forest\u2019s audion [1]), the mercury arc-rectifier marked the birth of power electronics

Brans-Dicke theory in the local potential approximation

We study the Brans-Dicke theory with arbitrary potential within a functional renormalization group framework. Motivated by the asymptotic safety scenario of quantum gravity and by the well-known relation between f(R) gravity and Brans-Dicke theory at the classical level, we concentrate our analysis on the fixed-point equation for the potential in four dimensions and with Brans-Dicke parameter omega equal to zero. For two different choices of gauge, we study the resulting equations by examining both local and global properties of the solutions, by means of analytical and numerical methods. As a result of our analysis we do not find any nontrivial fixed point in one gauge, but we find a continuum of fixed points in the other one. We interpret such inconsistency as a result of the restriction to omega equal to zero, and thus we suggest that it indicates a failure of the equivalence between f(R) gravity and Brans-Dicke theory at the quantum level.Comment: 34 pages, 8 figures; v2: corrected some misprints, added a new figure, four new references and some clarifying comment

One-loop renormalization in a toy model of Horava-Lifshitz gravity

We present a one loop calculation in the context of Horava-Lifshitz gravity. Due to the complexity of the calculation in the full theory we focus here on the study of a toy model, namely the conformal reduction of the z=2 projectable theory in 2+1 dimensions. For this value of the dimension there are no gravitons, hence the conformal mode is the only physical degree of freedom, and thus we expect our toy model to lead to qualitatively correct answers regarding the perturbative renormalization of the full theory. We find that Newton's constant (dimensionless in Horava-Lifshitz gravity) is asymptotically free. However, the DeWitt supermetric approaches its Weyl invariant form with the same speed and the effective interaction coupling remains constant along the flow. In other words, the would-be asymptotic freedom associated to the running Newton's constant is exactly balanced by the strong coupling of the scalar mode as the Weyl invariant limit is approached. We conclude that in such model the UV limit is singular at one loop order, and we argue that a similar phenomenon can be expected in the full theory, even in higher dimensions.Comment: 18 pages. v2: corrected some misprints, added 3 references, some clarifying comments and a new appendi

Single-Photon Observables and Preparation Uncertainty Relations

We propose a procedure for defining all single-photon observables in terms of Positive-Operator Valued Measures (POVMs), in particular spin and position. We identify the suppression of $0$-helicity photon states as a projection from an extended Hilbert space onto the photon Hilbert space. We show that all single-photon observables are in general described by POVMs, obtained by applying this projection to opportune Projection-Valued Measures (PVMs), defined on the extended Hilbert space. The POVMs associated to momentum and helicity reduce to PVMs, unlike those associated to position and spin, this fact reflecting the intrinsic unsharpness of these observables. We finally extensively study the preparation uncertainty relations for position and momentum and the probability distribution of spin, exploring single photon Gaussian states for several choices of spin and polarization.Comment: 25 pages (7 Figures); revised and extended version; in submissio