For nearly 40 years, optical fiber companies have been making single-mode silica fiber waveguide, with the best loss about 0.16 db/kilometer. This allowed a maximum distance between amplifiers of 125 kilometers, which is fairly good. But it did not get appreciably better. You wanted more, although you didn't know how it could be done. Which is strange, because from about 1970 to the early 1980's fiber went from about 100 db/kilometer to 0.16 db/kilometer in a tour-de-force of purification, a factor of about 600 in loss. So, why didn't the industry continue to improve, going from 0.16 db/km to 0.016 db/km, to 0.0016db/km, and even to 0.00016db/km, another factor of 1000 reduction in loss?

If fiber had a loss of 0.016 db/km, signals could travel 1250 kilometers without an amplifier, nearly 1/4 of the way across America. If fiber had a loss of 0.0016 db/kilometer, signals could travel 12,500 kilometers, and that's about 1/3 of the way around the world. If fiber had a loss of 0.00016 db/kilometer, signals could travel 125,000 kilometers, about three times around the Earth, needing no amplification.

But that's impossible, right? 40 years ago, before many people in your industry were even born, scientists got the materials put into fibers so pure and refined, and for some odd reason, they never got losses substantially smaller than 0.16 db/kilometer. They brought iron and other transition metal contamination down to parts-per-billion levels, and might have tried parts per trillion, and for some odd reason, the loss simply hovered at 0.16 db/km. They developed a process to chlorinate the silica soot, dramatically reducing the hydroxyl content. And it worked, mostly. Eventually, they even soaked the fiber in deuterium, to substitute the hydroxyls with deuteroxyls, and developed low-water-peak fiber. As if by magic. But what should have frustrated the fiber optic scientists and engineers was fiber's persistent hold on that loss of 0.16 db/kilometer.

I believe I've solved that problem. I asked the question, "What remains in the fiber when you take out all the contaminants you know of?" The answer? You still have the contaminants you DON'T know of. And that sounds like a strange statement, because what remains in the fiber, and especially the core? If you think like a chemist, you realize there is silica and germania, and very little else. But that's not a complete answer. You also have to think like a physicist. Elements like silicon, germanium, and oxygen are an incomplete description. Silicon in nature consists of silicon-28, silicon-29, and silicon-30 isotopes. Germanium in nature consists of germanium-70, germanium-72, germanium-73, germanium-74, and germanium-76. Oxygen in nature consists of oxygen-16, oxygen-17, and oxygen-18. Learn more at WebElements Periodic Table » Germanium » isotope data

If you took chemistry in high school, or even college, you might have learned that the difference between isotopes of the same element are the number of neutrons present in the nucleus. Silicon-28 has 14 protons and 14 neutrons. Silicon-29 has 14 protons and 15 neutrons, And silicon-30 has 14 protons and 16 neutrons. But their weight isn't the only difference. If a nucleus has an odd (not evenly divisible by 2) number of neutrons, that nucleus has an unpaired neutron, which causes that nucleus to wobble a bit. And the rest of the nucleus (which is positively charged, from all the protons) wobbles around the center of mass, which amounts to a tiny loop of electric current that never ceases. So, that nucleus behaves as if it was a tiny magnetic dipole, which of course it is. Silicon-29 and Germanium-73 have an odd number of neutrons, so they both have a small magnetic field associated with the nucleus. And silicon-29 is about 4.44% atom/atom of natural-isotope silicon. And germanium-73 is about 7.8% of natural-isotope germanium.

Light consists of an electric field and a magnetic field, at right angles to each other, both at right angles to the direction of the motion of the light. Light

When optical fiber companies make their fibers, they almost always use the elements the way they get them from nature, including the isotopic distribution which is normally seen in nature. "Why shouldn't we?", you might hear they'll say if you asked the question. They didn't know there was a difference. But I believe that when they use that Si-29 isotope, and that Ge-73 isotope, the passing light torques, or kicks, the atoms that have magnetic fields associated with their nuclei. And this converts a very tiny amount of energy from light (infrared) to a mechanical vibration, called a 'phonon': A phonon is like a sound wave, but in this case it's at a far-higher frequency, the same frequency of the photon which caused it, about 200 terahertz for a photon of wavelength 1500 nanometers. And those phonons eventually show up as a tiny amount of heat in the fiber itself, but not enough so that anybody would notice. But what you DO notice is a small loss in signal, about 0.16 db/kilometer.

I think that the vast majority of that residual 0.16 db/km loss in natural-isotope silica optical waveguide is due to Si-29 and Ge-73 isotope atoms in the silica and germania making up the fiber. There may very well be almost no other sources of loss from any other component. So, I believe that reducing the proportion of Si-29 and Ge-73 in the chemicals making up the fiber will dramatically reduce the fiber's optical loss.

Fortunately, nearly-isotopically-pure silicon-28 already exists. It was made for the Silicon Kilogram Project. Kilogram: Silicon Spheres and the International Avogadro Project

Is your company interested? Because the other ones will be!!!

Jim Bell