HISTORY OF FIBER OPTICS

This week’s History of Fiber Optics comes from George Gilder…Einstein asserted a radically new model for eltromagnetic radiation, he said, “Light consists of discrete photons.” Far from being in any sense continuous, radiation was emitted at high temperatures only in small bands separated by enormous gaps. In 1909 Einstein further summed up his argument in a speech by making a point that is crucial to communications technology when he used quantum theory to explain that light propagations could be reversed. Einstein cited experiments with Cathode rays and X-rays that demonstrated such “essentially inverse processes” as he put it.

These inverse processes are now crucial to lasers, photo-detectors, light-emitting diodes, and other devices that make fiber optics and photonics technology possible. Sitting in Einstein’s audience, Max Planck rose to object. “I am almost astonished,” he said, “that there did not arise more opposition and objection to this theory.” Planck pointed out that for quanta to show demonstrable interference effects that constitute the very definition of Einstein’s waves in space, they “would have to have a spatial extension of hundreds of thousands of wavelengths.” Planck was understandably rejecting the now familiar quantum paradox of particles manifesting wavelike interference patterns or waves emerging in particle concentrations.

The same Einstein, who almost failed at college, was some twenty years ahead of his audience. Rather than discard Maxwell’s equations, Einstein proposed to integrate classical wave theory with quantum theory as it is today, he noted that a photon behaved in some ways like an electron, in some ways not. “The field as produced by atomistic electric particles is not essentially distinguished” from the field associated with a particle of light. Einstein was predicting the next twenty years of quantum electrodynamics-the work of Louis Broglie, Paul Dirac, Werner Heisenberg, and Erwin Schroedinger-which would describe all quantum entities in terms of wave and particle duality.

By that time, Einstein himself would be refining his theories of relativity, which in their assumptions of continuity were ironically incompatible with his quantum theory. For the purposes of creation of the specific devices of telecommunications, however, Einstein’s pinnacle came in 1917. In calculations of that year, he offered what was perhaps his most fertile telecommunications idea: the simulated emission of radiation. Now embodied in the laser, Einstein’s concept relied on Niels Bohr’s atomic model. Bohr’s model hypothesizes that the electrons in an atom occupy a limited set of discrete energy levels or orbits. When an electron moves up or down, from one energy level to another, it emits or absorbs photons and of a definite frequency; when an electron increases its energy level it absorbs photons and when it decreases, it emits photons. These reciprocal processes manifest themselves in a fluorescent light, which is a glass tube filled with neon, mercury, or sodium gas which lights up when suffused by an electrical current or stream of electrons that excite the atoms in the gas to a higher energy state. They excite the atoms in the gas to a higher energy state and then as the gas atoms tumble back down to a lower energy level, they emit ultraviolet photons that excite the phosphorescent chemical coating of the lamp. Einstein’s vision of stimulated light clearly differentiates it from all other light we see, because Einstein’s enhanced light emissions have the property of coherence: its waves are all the same length, lined up in the same phases of crests and troughs; this light constitutes a beam of powerful intensity because it contains the amplitude of the original photons multiplied exponentially.

The Waynedale News Staff
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