Faster! Less money! Unfortunately this trend is true for computers and not for sports cars. An ever-growing demand for faster, yet economical communications exists. However, trying to process reams information in a supercomputer is like trying to get thousands of commuters to work on time. The faster we get the drivers to work, the quicker the work gets done.

Electrons inside a computer chip are not like race cars merrily zipping around Daytona Speedway. They're more a kin to traffic on the Los Angeles freeway--backed up, bunched up, and bogged down. While a large number of cars do make it through the maze during rush hour traffic, the individual driver takes a considerable amount of time getting to work. Continuing this analogy, an electronic transistor shortens a driver's commute by using a form of mass transit. When a bit of information is shoved into one end of a wire, the original electrons carrying this information are not the same ones that deliver it at the other end. Rather, the electrons smack into each other, one after the other, until some of them get shoved out the other end. However, even at today's clock speeds this "bus trip" distorts a signal trying to make it to the other end of a mother board, drowning it in traffic noise.

Unfortunately, using transistors in a computer chip can also be likened to putting stop lights on a freeway. They direct the moving streams of electrons from one intersection to another, but because of inductance, capacitance, and resistance, traffic gets all bunched up behind the red lights. On green electrons have to wait their turn to accelerate up to speed, only to pile into one another at the next red light.

As a result, chip designers are forced to slow down the traffic flow to maintain some semblance of order within the whole process. The composite electronic device plods along having to wait for the slowest parts to catch up with the rest. This bumper-car action between silicon stop lights, makes each electron less like an automobile, and more like a horse cart full of lead bricks. It will get the driver to work, but not in any real hurry.

Chip designers are doing everything they can to get the lead out. First they put in lots of traffic lanes, then they put the stop lights closer together. Switching times decreased, current flow and heat dissipation were reduced, information processing got a little quicker. So every few years they come out with a new and improved silicon road maze for electron bumper-cars.

The bumper-car effect prevents traffic lanes from being put very close together. As the stop lights get closer, fewer electrons make it through. Soon traffic at one light is slopping back into the light before it. Thus, the inherent construction of electrons makes them less than ideal information carriers.

The ideal information carrier would have to be free from inductance, capacitance, and resistance. It must move rapidly and directly from source to destination. Lanes must be able to crisscross each other simultaneously in the same 3-D space without any degradation in signal quality or cross talk between channels. It must be able to sort, select, switch, and direct the traffic flow instantly. Every channel must be an express lane. Everything must move at the same speed, top speed, all the time. No slow downs, no pileups.

Squashed into gas fumed grid lock, each driver sees the stop light change long before the cars get moving. If all drivers could get to work at the speed of light, "rush hour" would become "rush second"! Replacing electrons with photons means that MegaFLOPS would become TeraFLOPS and beyond. Thus, light is superior to electricity; it is the ideal information carrier.

But, how do these qualities figure into real photonic computers? The best electronic gates can switch a little better than 10 times in a nanosecond. If they are really tiny and placed extremely close together the switched signal (but not the exact electrons themselves) may have made it a hair's width through the semiconductor. However, in that same nanosecond, photons carrying that exact same bit of information will have traveled nearly a foot. photonic transistors can be made about as small as electronic ones, so same that same bit of information could have been through millions of operations in that same nanosecond. Why? Because the light pulse doesn't bog down at each gate. It can be sent through millions of photonic transistors in the same time as electrons take to wade through only a hand full. Thus, computers made with photonic transistors will be able to operate hundreds of thousands of times faster than their electronic counterparts...even in serial.

MASSIVE PARALLEL ARCHITECTURES

Broken down into individual little pieces, or pixels, that single image becomes millions of individual information-carrying beams of light. In a photonic computer each beam of light can undergo millions of calculations in a short amount of time and space. That single image represents not just millions of individual pixel beams, but millions of operations preformed on millions of beams simultaneously. Because these composite images are continually being modified as computation proceeds within the photonic transistors, they are called "Dynamic Images." Electronic circuits are simply left in the dust when trying to match that kind of "massive parallelism."

WHAT PHOTONIC TRANSISTORS ARE MADE OF

As you might expect, photonic transistors are not whittled out of silicon. Instead they are made out of photographs. Inexpensive photographs. While the many beams could be interconnected using conventional optics, the versatility of the hologram makes it an ideal medium for hooking photonic transistors together and interconnecting photonic-transistor-produced dynamic images. Holographic interconnection has been a part of the present technology for nearly 20 years. What's needed are functioning photonic transistors to complete the interconnection.

HOW PHOTONIC TRANSISTORS WORK

In order to be practical, photonic transistors must be simple. They must be easy to design, interconnect, and manufacture. They must be easy to understand. In order to be patented they must be so simple that people say, "Now, why didn't I think of that?" So, among all of these massively parallel light beams, carrying immense amounts of information at the speed of light, let me focus on one tiny little function of one tiny little photonic transistor and show you how it works.

Taken at their most basic level, electronic computers operate using only a small number of circuit types repeated many times over. The transistors used to make them are arranged to imitate Boolean algebra. These simple operations can be combined to from all of mathematics; thus, they can form all of computing. Some of these basic operations are OR, AND, NOT, and exclusive OR (abbreviated XOR.) Connected together they make up the familiar NOR and NAND gates worked with in electronics design every day.

According to Boolean math, only two are required to produce all of the others, and all of computing. For example, an AND tied into a NOT makes a NAND. If you wanted to, you could make an entire computer composed strictly of 74LS00 NAND gates, even if each pulse does waste 10 ns to travel from an input pin to its output pin.

While the NANDs and NORs are most common in electronic computers, two others are of special interest in photonics. They are the OR and the XOR. I'm sure examples of these two types of circuits are familiar to you.

As with the other boolean functions, combinations of these two types of circuits can create all of mathematics and every type of circuit that a computer needs, including memory. The photonic transistor preforms these two functions beautifully and swiftly, along with signal amplification, and a number of analog functions.

THE LIGHT AT THE END OF THE TUNNEL

Back in 1801 Thomas Young preformed an experiment that proved that light does has a wavelike nature. He did this by setting up an experiment whereby two beams of light from a common source were superimposed upon each other (see Figure 1). The light pattern produced was called interference, which can be measured in a manner similar to ocean waves. Later individual photons were also shown to possess this ability.

Today, we commonly use lasers and a Michelson Interferometer to demonstrate the effects of interference, even though the geometric configuration of the Young experiment differs from Michelson's. What is important here is that two beams of light from a coherent source are recombined by superimposing one beam on top of the other.

Figure 2--The three combinations of two input beams produce:(1) Both inputs off, no light output; (2) One beam on, even light distribution through the area; (3) Both beams on, light concentrated into the smaller areas of an interference fringe. By separating the fringe component regions into destructive interference (DI) areas and constructive interference (CI) areas, the photonic transistor is able to produce the Boolean OR and XOR functions, signal amplification, and analog signal processing.

Figure 2 is a close-up of the light pattern in figure 1. It has three sections, so first examine the lower one that shows the bands of light and dark. This figure illustrates what is called an interference fringe, which results from the recombination of two beams. The light portion is called constructive interference (CI) and the area of darkness called destructive interference (DI). (These terms are misnomers, for nothing is really constructed nor is anything destroyed.)

Photons affect one another differently when the two beams are traveling together than when only a single beam is present. When both beams are on, interference causes the photons to migrate toward each other. Photons that ordinarily would have been flying in the DI areas have been pulled to the side into the CI areas.

However, when only a single beam is on, no interference is present, and the entire area is illuminated as depicted in the center section of Figure 2. The photonic transistor exploits this natural effect in order to produce the two Boolean functions, OR and XOR.

Like all Boolean operators, the photonic transistor has two inputs; the two light beams of Figure 1. Switching these beams on and off can represent binary bits of information. Now take a look at the top section of Figure 2. It has no light at all, representing when both beams are off, a moot case. Thus Figure 2 depicts three states:

1. Both inputs are off, there is no light input.
2. If either one, or the other is on, the area is evenly lit although no interference fringe exists.
3. When both beams are on, the interference fringe forms.

A PHOTONIC OR

Place the paper so that the hole is lined up with the area "A" in Figure 2 labeled "A". In the moot case, both beams are off, so no light is output through the hole.

Now move the paper down to the center section to area "B". This point represents the exact same location as A, only now one of the beams has been activated. Note that either beam will turn on the output. Although there is no interference fringe, light is still output through the hole.

Now move your paper down to the lower section, to the area labeled "C". Again, this point represents the exact same position, only now both beams are on and the interference fringe has come into existence. Note that light is output through the hole. In fact, the light coming through the hole is 4 times brighter because of the CI than it is when only one beam is on at position B. That there is output through the hole in the paper mask when both input beams are on is what is important.

In your hand you hold a photonic transistor, albeit macro in size and crude in appearance. In this position relative to the fringe, it provides the OR function. Light coming from the paper, through the hole in the mask to your eye travels at the highest speed known. It didn't have to slow down or introduce any delays in providing this basic function.

A PHOTONIC XOR

Now move the mask so the hole is over position "F". What's different? Both beams are still on, but because of the DI, the photons have been shoved to the side, out of alignment with the line of sight through the hole. The input light is now reflected into another pathway, absorbed, or whatever by the mask. So the output through the hole is OFF. The device is a light-speed XOR.

Notice that without the mask, light from the two inputs would still exist in the output. Without the separation of these fringe component regions, the function is lost. The information manifested by the existence of the fringe disappears when beams of light from the separate regions is mingled back together again. Only with the mask in place does a separation of the information occur in the fringe component regions.

OTHER FUNCTIONS

An interesting thing happens, though, when a CI positioned mask is operated with one beam always on. When the second beam is off, the output is on because this constant "bias" beam is on. Now, when the second beam is turned on, interference relocates photons that used to be in the DI areas into the CI areas, and through the hole to become the output. The intensity is now four times greater than it was with only one switched-on beam. How can that be?

Say that in a certain time, 200 photons enter from one beam, and if the second beam is on, 200 photons from it. With only one constant bias beam on, the first 200 photons are spread over the entire surface of the mask. If the hole in the mask is over only the CI area, half of the light will go through the hole, and half of it will be stopped or diverted by the mask. So the output through the hole will be just 100 photons.

When the second beam comes on, the interference focuses all of the light into the CI areas. So that, along with the original 100 photons coming through the hole, the other 100 of the bias beam are shoved over into the CI area, and through the hole. At the same time, the second 200 from the other beam are also focused out through the hole, so the total output is 400 photons.

Because the constant bias beam carries no information, the modulated signal output is greater than it was in the beginning. By using additional photonic transistors or by phasing pulses to change the fringe position, combination photonic transistors can be constructed that, when both inputs are on, remove the constant 100 photon carrier from the output while not harming the 400.

Therefore, the photonic transistor is an amplifier like its electronic cousin. Granted, the gain is small. But that this gain exists even in these primitive examples is what is important. By using optical systems that change the shape of the fringes, and the proportion of DI area to Ci area, the actual gain may be tuned for optimum performance. Then, a number of photonic transistors can be cascaded together to produce appreciable gain.

Please note this is signal and is not light, the type that takes place in lasers. That is a different process, for a different purpose.

A CI device and a DI device can be made from the same mask simply by adjusting the position of the fringe. The fringe position can be shifted by a slight phase change in one of the beams. This adjustment also makes the photonic transistor into a demodulator for phase-modulated signals, because the resulting output is amplitude modulated.

Figure 3-- Photonic transistor demonstration using a Michelson Interferometer with a fring component separating mask placed between the beam combining optics and the viewing screen.

A SIMPLE DEMONSTRATION

The switching speed of a particular photonic transistor is the time it takes light to travel from the beam-combining optics to the mask. The closer they are together, the faster the transistor. Anything smaller than about an inch is faster than the fastest electronic transistor. So imagine what kind of speed is possible with microscopic components.

In production, photonic transistors can be made very small--near the size of the wavelength of light being used. The higher the frequency, the shorter the wavelength. The shorter the wavelength, the smaller and more closely they can be packed together, and the faster the computer.

DEVELOPMENT

Photonic transistors are so general in their nature that predicting which products will be developed first is difficult. As with electronic transistors, they are applicable to just about everything. The first products will be software for the production of photonic transistor photographs and interconnecting holograms, demonstration products, and individually connected photonic transistors. These are expected very soon, as we arrange R&D with the variety of interested groups both large and small. The next products are expected to be specialized devices, such as telephone fiberoptic switching systems, and add-on products for speeding up electronic processing. Then of course, fully photonic teraFLOPS computers as the photonic-transistor-producing software becomes operational.

Will there be problems in the coming photonic development? Certainly, there will always be challenges. However, those difficulties will not arise from any need to research and create specialized materials as with other optical methods or to figure out some unknown quirk of physics. Rather, they are merely the geometric problems of engineering the organizational and architectural arrangement of components, using optical laws that are well understood.

There is another important reason why photonic development will be much more rapid than was the development of its electronic counterpart. Although, the photonic transistor stands today where the electronic transistor stood 40 years ago, the great body of computer science was in its infancy. Modern-day manufacturing technology didn't exist. The pictures that were used to fabricate the first computer chips were drawn by hand. The entire ordeal was time consuming. Early electronic transistors had to be individually wired in by hand. Printed circuits didn't exist.

Today, the art of holography is well understood and is used to interconnect digital light beams. Like other photographs, holograms and the photographic masks that make up photonic computers, can be produced by computer, calculated into existence from the basic math they are derived from. The well-known laws of optics, existing equipment, hologram-producing programs already available, and the principles of the photonic transistor are the ingredients for the development time acceleration of photonic computers.

Today's tools are much faster than those of yesteryear. Computer aided design compresses years of development time into months or even hours. The great body of computer science is mature and well adapted for each new computer upgrade and is poised for the photonic conversion, which will just be the next, upgrade.

Remember what happened to the slide rule?

The End

John Hait is an electronics engineer with 35 years of experience in basic circuit design and troubleshooting electronic and data processing systems. He is best known by his books and articles on practical applications of thermodynamics and electrochemistry. He is the inventor of the photonic transistor, which is only one of 85 inventions that span the wide spectrum of practical physics.

Copyright Circuit Cellar INK, The Computer applications Journal Reprinted by permission.

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