With High Definition Television looming as a requirement, it looks as though we are going to be faced with moving enormous amounts of data at ever increasing speeds. With mega-bits increasing into the high giga-bits, the systems we have been using are not good enough. The same thing happened when colorcame to television. At the end of an amplified line we saw not only very pale colors, but the wrong colors. Our amplifier and line systems were inadequate. Whether you are involved with HDTV or not, fibre optics will be a part of your future.
    Karl Gauss and James Maxwell were among many who did extensive studies of Hertzian waves. Their conclusions were that light was just an extension of these waves, but at much higher frequencies. That is, the theories that applied to "radio waves" applied to the much higher frequencies of light and X-rays.
     Visible light extends from just below 700 millimicrons to just beyond 400 millimicrons, about an octave. Infrared, quite useful in fibre optics around the 1080 nm wavelength, and ultraviolet just above the visible in frequency, are part of this useful spectrum. These have their center around the 300
Terra-hertz frequency. But can we look at these frequencies as conforming to the "wave theory" that we have spent our careers manipulating? The answer is both yes and no.
     We apply the wave theory to our familiar "radiowaves", but when it comes to infared and above, strange things seemed to happen . . .and then came Max Planck and his quantum theory, and things of which we were so sure, seemed to go awry.
    When Phillip Lenerd explored the effect of ultraviolet light by producing a positive charge on zinc by knocking out an electron, it meant that the wave theory was in question. This phenomenon was taken under study by Albert Einstein.
     Leery of the quantum theory, Einstein produced a paper explaining the effect of a quanta packer of energy he called the proton. The photon’s energy level was related to frequency.  Somehow the quanta pack of infared did not seem to contain enough energy to dislodge an electron, but ultraviolet succeeded. The energy level was related to frequency. To make things even more confusing a single photon had to have enough energy level by itself. Two, or even twenty-two, could not gang up and knock out the electron producing what we know as the photo electric effect. It seemed that the photon theory had come to the fore.  These discoveries were very upsetting to the world of physics.  The wave theory, and the partical/photon theory seemed to be incompatible with each other.
     Proof of the wave theory had been enhanced by Thomas Young around 1900. By passing light through very small slits and combining them on the opposite side, he discovered that light and dark interference patterns of the waves combining were just as you would expect if you let two frequencies, slightly displaced, combine. If the light was a quanta of photons, they would splatter in specks on a screen, maybe?
     Something else added to the confusion. We know if we take a frequency and full wave rectify it, and with a little filtering, we will wind up with twice the frequency. In other words, we have doubled the frequency. Surely this cannot apply to light can it? Yes it can! If you take a beam of deep, red frequencylight, and pass it through a cut crystal of dihydrogen phosphate, it will come out the other side as a violet light, doubled in frequency from the input. You can easily see the great variety of tools we have at our hands when use light energy to carry out information.
     The Navy has used the flashing of a light to send signals for generations. Limited only to skill and mechanics of the operation, the speed of transmission was about 4 to 8 bits per second, based on the data compression of the codes used. A fiber optics system can "blink" many billions of times faster.
     A fiber optic system usually consists of a LED focused into a fiber of about 5 to 10 microns. Plastic fibers are less expensive, but have more attenuation than those of silica.  At the receiver end, the light is focused on a reversed biased pn diode in which electron-hole pairs are swept apart, with the result of a photocurrent occurring whether photon strikes the diode. Diodes are made of indium usually have longer lives than those made with aluminum. Modulation and demodulation is done with conventional circuits. The simplest and least expensive link uses a plastic fiber and operates with visible light have a peak wavelink of about 665 nanometers, about 450 Terrahertz. By relying on the wave theory, two things must always be in your mind:

**The numerous references required to produce this article  are available from SBE Chapter 105, or: R. Claude Burrows.