Why compute with light?

In a nut shell, the photonic transistor products, which are expected to replace much of the electronics infrastructure during the 21st century, can be made smaller, faster, and cheaper. They are more reliable, generate less heat, and are not susceptible to interference from outside influences. In comparison to photonics, even the best electronics is slow, because photons are faster than electrons.

How fast?

Unlike electronic circuits, photonic circuits process information by manipulating light with light at the speed of light. The amount of information that can be processed in one second depends on how fast the components in the circuit are able to control information.

Until the invention of the photonic transistor, it was generally thought to be impossible to switch one beam of light on and off with another beam of light, which is necessary in order to manipulate information and perform computing functions completely in the light-speed optical domain. However, the photonic transistors now being developed by a local San Diego firm are currently switching light in 1.5 femtoseconds (fs). (One millionth of a billionth of a second.) The photonic transistor truly is the first method developed that switches light with light at the full speed of light.

To be precise, photonic transistors have been produced that react to photonic signals in the time of one cycle of one wavelength of the light being used. For red light that switching time is about 2.1 fs. Blue is about 1.5 fs, with the 1500 nm light used in fiberoptic communications switching in 5 fs.

Why are photonic transistors able to manipulate information nearly 100,000 times faster than electronic transistors?

Simple! Photons of light are comprised of octagonal electric and magnetic fields that propagate at 186,000 miles/sec (300,000 kps) in a straight line. Electrons are also made of fields of flowing energy that propagate at light speed. However, the propagation paths of the energy in an electron circulate around following the physical shape of the electron itself. Consequently, in order for an electron to physically move from point A to point B, the energy must circulate around the electron along a curved path, while the whole circulating field structure migrates its way over to B. Because all energy moves at the same speed, the energy in the electron takes longer to get to B simply because it must cover a longer circulating distance than the energy in a photon, which makes a straight shot of it.

This circulating energy pattern within the electron is also the reason why it's able to stay in one place, while the photon is not. The same feature that makes electrons inherently slow.

Is the market ready for light speed?

In recent years the demand for bandwidth (information carrying ability) has increased so rapidly that the electronics industry has been forced to push the electron to its physical limits. But, the structure of the electron itself presents a physical barrier that cannot be surpassed by any circulating field system such as an electron, atom or molecule. So, the closer technology pushes the electron to its limits the more their costs go expotential.

That demand for ever faster computers, and communications equipment is expected to mushroom as more and more people come to expect broadband services. Since the industry is now pushing the electron to its limits, the only alternative is light.

Why is it that light is able to do so much more than electricity?

In addition to the photonic transistor's ability to switch in one cycle, the structure of light is quite different from the electron. At any given instant, all of the information on an electric conductor is a function of just one variable... the electric charge at that location. Each photon, on-the-other-hand, being quantum, provides an independent information-carrying variable for each independent photonic frequency or color.

So the capacity of light to carry information in serial surpasses electronics because of light's physical structure, but a multi-colored beam of light is like a parallel bunch of wires where each "wire" is a different color.

How many colors are there?

Visible light is a small part of the electromagnetic spectrum, like radio waves only having carrier frequencies in the terahertz (trillion cycles per second) range rather than the megahertz range. The photonic transistor has been shown to have a tuning and filtering resolution finer than that of an AM radio. So, if just the visible portion of the spectrum were to be divided into AM radio-wide-bands there would be over 35 billion separate channels. In a computer, that's like having a bus width of 35 billion rather than the paultry 64 or 128 bit buses that have so greatly increased the speed of today's computers.

How much information can a single beam of light carry?

Each color can, in theory, carry over 200 terabits of information per second. The entire Library of Congress has only about 30 terabits of information in it. Multiply that times the number of colors and it represents a gigantic amount of information carrying capacity. But not just for transmission through optical fibers and the like. Since the photonic transistor is able to manipulate those bits in the optical domain just as nimbly as electronic transistors manipulate the information in electronic circuits, nearly every information processing device can now be produced using light speed photonics.

Why use holograms to replace computer chips?

Holograms are just one method for making photonic transistors. They can be made with optical fibers, and a host of other optical methods. However, computer generated holograms have the ability to imitate nearly any ordinary optical setup. The complexities of optical integrated circuits can be calculated into a set of holograms that enable the light to manipulate the light in complex photonic circuits. The architecture is similar to that used in electronic computer chips. It's just faster and less expensive to manufacture.

How can photonic transistor products be made "smaller" than their slower electronic counterparts if they are limited by the size of the wavelength being used?

The tremendous bandwidth of light can be used in our patented Frequency Multiplexed Logic photonic transistors. By this method, a single physical device can substitute for a billion devices of a typical electronic architecture. Since so much can be done with so few physical devices, the total transistor count is much smaller. Consequently, the complete apparatus can be made much smaller than its electronic equivalent when comparing apples with apples, i.e., bandwidth for bandwidth.

Why can photonic transistor circuits be made cheaper than electronics?

High speed electronics... that is, the best that can be achieved, takes extremely pure materials and extremely precise manufacturing equipment that can control manufacturing down to the size of an atom. One atom out of place and the part fails. Photonic transistors can be made of glass, plastic, aluminum and other common materials. Manufacturing tolerances are well within the capability of a growing number of commercial optical manufacturing methods. And, some manufacturing methods can actually stamp out photonic transistor holograms.

What about noise?

Unlike electronic circuits, conventional optical amplifiers and many nonlinear optics, the light in photonic transistors does not interact with the material of which the transistor is made, in such a way that would add noise to the signals passing through. One reason for this is that the process of optical interference, that the transistors are based on, involves only the redistribution of energy rather than absorption or re-emission of energy that can produce heat, which in turn could introduce noise into the signals.

When can we expect to see photonic transistor devices on the market?

Logically, we have no reason to push the photon to its limits at this time. We only have to beat the slugish electron in order to beat the electronic or even the optoelectronic competition.

What about competing optical methods?

The search for specialized materials that would do what photonic transistors are already doing has been a well funded failure among many companies, large and small. Discovering a practical switching material has been so difficult that the Wall Street Journal (Jan. 30, 1990) labeled it "unobtainium." The picture hasn't improved much since. So far, the nonlinear optical materials being developed have only been able to switch in several thousands of femtoseconds. However, the greater continuing problem is that, as the pulse repetition rate exceeds 30 mhz or so, they incinerate themselves!

Their fundamental operation depends on altering the properties of these special crystals using powerful light beams. Whereas the interference-based photonic transistors can operate using only a couple of photons. Even if someone does discover an efficient, low power "unobtanium," it still must be manufactured into photonic microcircuits. Not to mention that no one has yet even suggested a method for doing frequency multiplexed logic with them to reduce component count and manufacturing costs. This is because the frequency range of nonlinear optical materials is restricted by the natural oscillations of the atoms which make them up.

What is the relationship between AON and the Rocky Mountain Research Center (RMRC)?

The photonic transistor was invented at RMRC and sold to Cyber Dyne Computer Corp., which is now All Optical Networks, Inc. So this information is presented in order to answer some of the most frequently asked questions about the photonic transistor, and to document RMRC's history of advanced science.

So, why compute with light?

1. Photons of light have the potential for manipulating information that far surpasses electronics, because photons can move faster than electrons... especially in semiconductors. Photons carry many orders of magnitude more information, produce substantially less heat, and are not subject to the restrictions caused by capacitance, inductance, resistance, and reluctance.

2. Computer generated holograms used to make holographic integrated circuits can be mass produced less expensively than microelectronics.

3. The demand for information services has forced the electronics industry to push the electron to its physical limits, so photons are the only option.

4. Why not? It's only logical.