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Photonic computing
Post: #1

Photonic Computing is digital computing in imitation of conventional electronic computing only using laser light instead of electricity, and holograms instead of silicon computer chips. "Photonic" comes from "photon" which is the smallest unit of light just as an electron is the smallest unit of electricity. "Photon" comes from "photo" as in "Kodak moment!" Uninhibited light travels thousands of times faster than electrons in computer chips; therefore it is capable of computing thousands of times faster than electronic computing. Therefore, light computers will compute thousand of times faster than any electronic computer can ever achieve due to the physical limitation differences between light and electricity.
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. 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.
1. What is Photonic Computing?
With todayâ„¢s growing dependence on computing technology, the need for high performance computers (HPC) has significantly increased. With the help of virtual product design and development, costs can be reduced; hence looking for improved computing capabilities is desirable. Optical computing includes the optical calculation of transforms and optical pattern matching. Emerging technologies also make the optical storage of data a reality.
The speed of computers was achieved by miniaturizing electronic components to a very small micron-size scale, but they are limited not only by the speed of electrons in matter (Einsteinâ„¢s principle that signals cannot propagate faster than the speed of light) but also by the increasing density of interconnections necessary to link the electronic gates on microchips. The optical computer comes as a solution of miniaturization problem. In an optical computer, electrons are replaced by photons, the subatomic bits of electromagnetic radiation that make up light.
Electronic computing uses electrons to perform the logic that makes computing work. Photonic computing uses photons of laser light to do the same job, only thousands of times faster. Electronic transistors are whittled into silicon wafers to make modern computer chips. Today's technology, however, is pushing the electron to its physical limits. As a result, the manufacturing processes are becoming increasingly expensive for producing even minor improvements. However, photons are manipulated using inexpensive computer-generated holograms made of plastic or glass. Photonic computers, therefore, will be far more valuable than their slower electronic counterparts, and far less expensive to manufacture.
Interestingly, most telephone companies have been investing heavily in the global conversion from copper wire to optical fiber because light does a better job of carrying information than does electricity. This is because photons (the basic unit of light) go faster, and have a higher bandwidth than do electrons. Bandwidth refers to the amount of information that can be transmitted simultaneously through a given device. Thus, photons are inherently more valuable than electrons. If we can just get them to accomplish the logic tasks that make computing work, they will become the next logical computing upgrade.
Over 65 major companies have invested heavily in the search for an inexpensive "nonlinear" crystal able to make one light beam turn another light beam on and off, which is a prerequisite for the production of a completely photonic (optical) computer.
Photonic logic, based on a different physical principle, is proving to be the key to the production of a completely optical computing system. Such a system would completely replace the start-and-stop surges of electrons with tiny light beams that simply blink on and off, in order to carry information and perform the logic of computing in light-speed photonic computers... without slowing down the photons in some crystal or enslaving them to some electro-optical process.
Post: #2

Electronic computing uses electrons to perform the logic that makes computing work. Photonic computing uses photons of laser light to do the same job, only thousands of times faster.
Electronic transistors are whittled into silicon wafers to make modern computer chips. Today's technology, however, is pushing the electron to its physical limits. As a result, the manufacturing processes are becoming increasingly expensive for producing even minor improvements. However, photons are manipulated using inexpensive computer-generated holograms made of plastic or glass. Photonic computers, therefore, will be far more valuable than their slower electronic counterparts, and far less expensive to manufacture.
Interestingly, most telephone companies have been investing heavily in the global conversion from copper wire to optical fiber because light does a better job of carrying information than does electricity. This is because photons (the basic unit of light) go faster, and have a higher bandwidth than do electrons. Thus, photons are inherently more valuable than electrons. If we can just get them to accomplish the logic tasks that make computing work, they will become the next logical computing upgrade.

However due to research in the field of Photonic Transistor, it is possible to generate logic gates by making one light beam turn another light beam on and off without the use of some electronic gizmo in the middle.
1.1 History of Electronic Computing
Computers have enhanced human life to a great extent. In recent years, personal computers have become increasingly important as machines to help us do all the work in an easy manner, any calculation that is done by a computer becomes computing.
The speed of conventional computers is achieved by miniaturizing electronic components to a very small micron-size scale so that those electrons need to travel only very short distances within a very short time. The goal of improving on computer speed has resulted in the development of the Very Large Scale Integration (VLSI) technology with smaller device dimensions and greater complexity. Last year, the smallest-to date dimensions of VLSI reached 0.08 mm by researchers at Lucent Technology. Whereas VLSI technology has revolutionized the electronics industry and established the 20th century as the computer age, increasing usage of the Internet demands better accommodation of a 10 to 15 percent per month growth rate. Additionally, our daily lives demand solutions to increasingly sophisticated and complex problems, which requires more speed and better performance of computers.
For these reasons, it is unfortunate that VLSI technology is approaching its fundamental limits in the sub-micron miniaturization process. It is now possible to fit up to 300 million transistors on a single silicon chip. It is also estimated that the number of transistor switches that can be put onto a chip doubles every 18 months. Further miniaturization of lithography introduces several problems such as dielectric breakdown, hot carriers, and short channel effects. All of these2factors combine to seriously degrade device reliability.
Even if developing technology succeeded in temporarily overcoming these physical problems, we will continue to face them as long as increasing demands for higher integration continues. Therefore, a dramatic solution to the problem is needed, and unless we gear our thoughts toward a totally different pathway, we will not be able to further improve our computer performance for the future. Optical interconnections and optical integrated circuits will provide a way out of these limitations to computational speed and complexity inherent in conventional electronics. Optical computers will use photons traveling on optical fibers or thin films instead of electrons to perform the appropriate functions.
1.2 What is Photonic Computing?
Today's computers use the movement of electrons in-and-out of transistors to do logic. Photonic computing is intended to use photons or light particles, produced by lasers, in place of electrons. Compared to electrons, photons are much faster “ light travels about 30 cm, or one foot, in a nanosecond “ and have a higher bandwidth.
Computers work with binary, on or off, states. A completely optical computer requires that one light beam can turn another on and off. This was first achieved with the photonic transistor, invented in 1989 at the Rocky Mountain Research Center. This demonstration eventually created a growing interest in making photonic logic componentry utilizing light interference.
Light interference is very frequency sensitive. This means that a narrow band of photon frequencies can be used to represent one bit in a binary number. Many of today's electronic computers use 64 or 128 bit-position logic. The visible light spectrum alone could enable 35 billion bit positions.
Recent research shows promise in temporarily trapping light in crystals. Trapping light is seen as a necessary element in replacing electron storage for computer logic.While photonic computing is still seen as impractical by many, research is being pushed along by strong market forces already implementing networking and, thus, creating opportunies. Recent years have seen the development of new conducting polymers which create transistor-like switches that are smaller, and 1,000 times faster, than silicon transistors.
Optical switches switch optical wavelengths. Optical switching, while not all-optical, has already become important in networking environments. 100 terabit-per-second data-handling is expected within the decade.
1.3 Photonics: a related term
Photonics is the science and technology of generating, controlling and detecting photons, particularly in the visible and near infra-red spectrum. Photonics as a science is closely related to quantum optics and optoelectronics with somewhat unclear boundaries. Quantum optics frequently implies fundamental research, while photonics often refers to more application-related research. The term optoelectronics, which by construction is a somewhat narrower field than photonics dealing only with active elements involving an electrical interaction, nonetheless frequently is used to include passive photonic elements as well. In addition, the overlap between all of these fields and "optics" is unclear, and different definitions are used in different parts of the world and in different industries.
The term photonics may, but doesn't always, imply a goal of establishing an electronics of photons instead of electrons.

Figure 1.1 “ Refraction of photons by a prism
The science of photonics includes the emission, transmission, amplification, detection, modulation, and switching of light. Photonic devices include optoelectronic devices such as lasers and photodetectors, as well as optical fiber, photonic crystals, planar waveguides and other passive optical elements.
Applications of photonics include:
¢ light detection
¢ telecommunications
¢ information processing
¢ illumination
¢ metrology
¢ spectroscopy
¢ holography
¢ medicine (surgery, vision correction, endoscopy, health monitoring)
¢ laser material processing
¢ visual art
¢ biophotonics
¢ agriculture
¢ robotics
¢ defense.
History of photonics:Photonics as a field really began in 1960, with the invention of the laser, followed in the 1970s by the development of optical fibers as a medium for transmitting information using light beams, and the Erbium-doped fiber amplifier. These inventions formed the basis for the telecommunications revolution of the late 20th Century, and provided the infrastructure for the Internet.
Photonics as a field was largely focused on communications. However, photonics covers a huge range of science and technology applications, including: laser manufacturing, biological and chemical sensing, medical diagnostics and therapy, display technology, and optical computing. Various non-telecom photonics applications exhibit a strong growth particularly since the dot-com crash, partly because many companies have been looking for new application areas quite successfully. A huge further growth of photonics can be expected for the case that the current development of silicon photonics will be successful.
1.4 Why Use Optics for Computing?
In the optical computer of the future, electronic circuits and wires will be replaced by a few optical fibers and films, making the systems more efficient with no interference, more cost effective, lighter and more compact. Optical components would not need to have insulators as those needed between electronic components because they do not experience cross talk. Indeed, multiple frequencies (or different colors) of light can travel through optical components without interfacing with each others, allowing photonic devices to process multiple streams of data simultaneously.
Optical interconnections and optical integrated circuits have several advantageous over their electronic counterparts. They are immune to electromagnetic interference, and free from electrical short circuits. They have low-loss transmission and provide large bandwidth; i.e. multiplexing capability, capable of communicating several channels in parallel without interference. They are capable of propagating signals within the same or adjacent fibers with essentially no interference or cross-talk. They are compact, lightweight, and inexpensive to manufacture, and more facile with stored information than magnetic materials.
Most of the components that are currently very much in demand are electro-optical (EO). Such hybrid components are limited by the speed of their electronic parts. All-optical components will have the advantage of speed over EO components. Unfortunately, there is an absence of known efficient nonlinear optical materials that can respond at low power levels. Most all optical components require a high level of laser power to function as required. A group of researchers from the University of Southern California, jointly with a team from the university of California Los Anglos, have developed an organic polymer with a switching frequency of 60 GHz. This is three times faster than the current industry standard, lithium niobate crystal-based devices. The California team has been working to incorporate their material into a working prototype. Development of such a device could revolutionize the information superhighway and speed data processing for optical computing.
A group of researchers at Brown University and the IBM Almaden Research Center (San Jose, CA) have used ultra fast laser pulses to build ultra fast data storage devices. This group was able to achieve ultra fast switching down to 100ps. Their results are almost ten times faster than currently available speed limits. Optoelectronic technologies for optical computers and communication hold promise for transmitting data as short as the space between computer chips or as long as the orbital distance between satellites. A European collaborative effort demonstrated a high-speed optical data input and output in free-space between IC chips in computers at a rate of more than 1 Tb/s. Astro Terra, in collaboration with Jet Propulsion Laboratory (Pasadena, CA) has built a 32-channel 1-Ggb/s earth to satellite link with a 2000 km range. Many more active devices in development and some are likely to become crucial components in future optical computer and networks.
Another advantage of optical methods over electronic ones for computing is that optical data
processing can be done much easier and less expensive in parallel than can be done in electronics. Parallelism is the capability of the system to execute more than one operation simultaneously. Electronic computer architecture is, in general, sequential, where the instructions are implemented in sequence. This implies that parallelism with electronics is difficult to construct. Parallelism first appeared in Cray super computers in the early 1980â„¢s. Two processors were used in conjunction with the computer memory to achieve parallelism and to enhance the speed to more than 10 Gb/ s. It was later realized that more processors were not necessary to increase computational speed, but could be in fact detrimental. This is because as more processors are used, there is more time lost in communication. On the other hand, using a simple optical design, an array of pixels can be transferred simultaneously in parallel from one point to another. Parallelism, therefore, when associated with fast switching speeds, would result in staggering computational speeds. Assume, for example, there are only 100 million gates on a chip, much less than what was mentioned earlier (optical integration is still in its infancy compared to electronics). Further, conservatively assume that each gate operates with a switching time of only 1 nanosecond (organic optical switches can switch at sub-picoseconds rates compared to maximum picoseconds switching times for electronic switching). Such a system could perform more than 1017 bit operations per second. Compare this to the gigabits (109) or terabits (1012) per second rates which electronics are either currently limited to, or hoping to achieve. In other words, a computation that might require one hundred thousand hours (more than 11 years) of a conventional computer could require less than one hour by an optical one.
Another advantage of light results because photons are uncharged and do not interact with one another as readily as electrons. Consequently, light beams may pass through one another in full duplex operation, for example without distorting the information carried. In the case of electronics, loops usually generate noise voltage spikes whenever the electromagnetic fields through the loop changes. Further, high frequency or fast switching pulses will cause interference in neighboring wires. Signals in adjacent fibers or in optical integrated channels do not affect one another nor do they pick up noise due to loops. Finally, optical materials possess superior storage density and accessibility over magnetic materials.
Obviously, the field of optical computing is progressing rapidly and shows many dramatic opportunities for overcoming the limitations described earlier for current electronic computers. The process is already underway whereby optical devices have been incorporated into many computing systems. Laser diodes as sources of coherent light have dropped rapidly in price due to mass production. Also, optical CD-ROM discs have been very common in home and office computers.
2.1 Silicon Photonics overview
Silicon photonics is the term which is the most recently used fro photonic computing as this deals with technology to make photonic devices which use the silicon as the source of the laser for the photon generation. Silicon is the principal material used in semiconductor manufacturing today because it has many desirable properties. For example, silicon is plentiful, inexpensive, easy to work with, and well understood by the semiconductor industry. Intel, in particular, has developed some of the most advanced silicon fabrication technology available today. Due to the company™s leadership in this area, it has long invested in research to siliconize other technologies, such as optical communications. This field”known as silicon photonics”aims to provide inexpensive silicon building blocks that can be integrated to produce optical products that solve real communication problems for consumers.
Silicon is an especially useful material for photonics components due to one key property: it is transparent at the infrared wavelengths at which optical communication operates. Therefore, while silicon is opaque to the human eye, it appears clear as glass to a laser operating at infrared wavelengths.
2.2 The silicon laser challenge
A key challenge facing the silicon photonics community is a fundamental physical limitation of silicon: namely, silicon cannot efficiently emit light. While it is capable of routing, modulating, and detecting light, silicon has needed an external light source to Pro vide the initial light.
These external light sources are generally discrete lasers and require careful alignment to the silicon waveguides. The problem is that accurate alignment is difficult and expensive to achieve.
Even submicron misalignment of the laser to the silicon waveguide can render the resulting photonic device useless.

A long-standing quest in silicon photonics has been the creation of a laser source that can be manufactured directly on the silicon photonic chip, in high volume, and whose emitted light is automatically aligned with the silicon waveguide.
To solve this problem, Intel has partnered with Professor John Bowers at UCSB, who has more than 25 yearsâ„¢ experience working with indium phosphide-based materials, lasers, and other compound semiconductor materials. During the past few years, he has developed a variety of novel photonic devices, including very high-speed lasers, modulators, and photo-detectors. Also, he has integrated them in advanced transmission systems at data rates as high as 160Gbps. In parallel, he has been developing waferbonding techniques to enhance the performance of these materials.
2.3 The photo transistor
In 1989 the Photonic Transistor was invented at the Rocky Mountain Research Center, and then tested in the laboratories of the University of Montana, and Montana State. In 1992, U.S. Patent 5,093,802 was issued to the Rocky Mountain Research Center. Since that time, the entire basis of interference-based photonic computing has been growing and growing. Even that crude first example was able to accomplish what the 'experts' said was impossible, making one light beam turn another light beam on and off without the use of some electronic gizmo in the middle.
Unlike the nonlinear optical materials that require a large supply of photons to bias them up to some switching level, Photonic Transistors need only signal levels of photons to work. Just as we can see certain things at night that emit only a handful of photons per second, so too, the Photonic Transistor must be able to operate using small amounts of energy.

The next desirable attribute is that they should always operate at the full speed of light. The fundamental physical control and manipulation processes used do not slow down the light. The only retardation occurs during the very short time that the energy must pass through a dense medium such as a thin hologram. The Photonic Transistor is vacuum compatible, meaning that they can be operated in air or even in a vacuum where there light moves at the universal speed limit.
In one second, electromagnetic energy can circle the earth seven and a half times in one second. In one nanosecond, (one billionth of a second,) light goes 30 cm, or about 11 3/4 inches. By measuring the dimensions of the smallest working model of our photonic transistor we can calculate the amount of time it takes light to pass through the device in order to accomplish the above photonic logic and amplifications functions. In a working photonic computer, these will be the switching times used to determine how fast we will be able to make a photonic supercomputer go.
First by way of comparison, so that we can realize the importance of what has been accomplished, the electronic transistors that perform logic in a $5,000,000 Cray III supercomputer are able to switch in about 0.25 nanoseconds using expensive gallium arsenide transistors. That translates into a 2 nanosecond clock cycle time which in more familiar terms is 500 MHz. So the new 200 MHz Pentium is getting up there. Of course it's tough to make $2000 Pentium machines out of materials that are needed to build a $5,000,000 Cray.
The test transistor was made using a piece of glass so that we could easily hold the image component separator still in relation to the beam combining optics. By calculating the distances through the glass, and the attached mask, the transit times were able to be calculated. Each one be built was progressively smaller until we reached the point there the transit time for 632.8 nm, red, laser light is 0.007 nanoseconds!
The Cray reportedly has transistors that switch in 0.25 ns. In that case it is roughly 35 times faster than the Cray.
2.4 Working of Logic gates
The basic element of a computer is the logic gate which performs the basic logical operations. And the first step to understand its working is to give it an input, information is carried on beams of light just as it is carried on a radio, television, or microwave signal. Here pulse coding is used both for carrying data and for opening and closing logical gates that direct photonic information around photonic circuits.
The organization of photonic logic stages imitates the organization of logic stages in an electronic computer because we want the photonic computer to do the same things that regular computers do...only faster. The basic switching functions of digital computers use Boolean logic. Invented by George Boole in the middle of the 19th century, Boolean logic functions are easily generated by machines. From a hand full of logic operators, entire computing systems are built by interconnecting millions of them in information-flow and control architectures. The result can be an IBM PC, a Pentium Pro or a hand calculator, but they all work the same.

Figure 2.1“ State1. Pulse at input
In this figure the small square at the top input is the data pulse, the two black rectangles are the holograms that are used to create the logic here it is OR and XOR.

Figure 2.2 “ State2. Pulse reaches the gate.

XOR output pulse. OR output pulse.
Figure 2.3 “ State3. Pulse reaches the gate.
Traveling at the speed of light, "on" pulses interact with the photonic transistor's hologram in different ways depending on the exact hologram, and the relationship of simultaneously-arriving pulses to each other.
In this first animated illustration, (state 1) an OR, and an XOR are shown. Each of these functions can be produced with the same hologram, the difference being the location from which the output energy is extracted. Thus, information about both functions is actually generated simultaneously, with the output energy from each one being directed as needed to subsequent logic stages.
As with any two-input binary device, there are four possible combinations of the input beams being instantaneously on or off: both off, the upper one on, the lower one on, and both beams on. These various input combinations are held steady during the entire pulse length so as to produce equivalently long outputs. The input pulse combinations produce four different images, or energy distributions that are projected onto the separator. The moot, or null output is produced when both beams are simultaneously off. Since there is no energy input, there is no energy output either through the hole or by reflection.
To the right of the figure 2 above, (state 2) the mask mirror is shown as seen from the hologram. in between pulses, no energy is available, and thus nothing goes through the exit hole. However, when the diffracted pulse reaches the mirror/mask the image component having the OR information exits the hole (state 3). The portion having the XOR information (the pulse heading downward away from the hologram,) is reflected by the mirror and on to the next logic stage, (state 3.).

3.1 Introduction to Silicon Laser
All the devices following the principle of silicon photonics need to have a source to generate photons of light by using laser (Light Amplification through Simulated Emission of Radiation.).
There are three laser setups famous in the silicon photonics technology. They are explained in the following few sections the Laser technique are:
¢ Hybrid Silicon Laser.
¢ External Cavity Laser.
¢ Continuous Silicon Laser.
Among all the lasers mentioned here the most advanced and the most appropriate is the hybrid silicon laser, yet the other two lasers have their own benefits which are discussed in the following few headings.

3.2 Hybrid Silicon Laser
The most recent researches in the world of silicon photonics have resulted to the answer of the question how to feed the silicon with photons.
3.2.1 Working of the laser
To understand the working of the Hybrid Silicon Laser which acts as the primary source of the photons for the working of the photonic computer let us first understand the detailed diagram of the Laser.

Figure 3.1 “ Cross-section schematic of a hybrid silicon laser.
Figure 3.1 is a cross-section of the hybrid silicon laser, showing the indium phosphide-based gain material (InP) that generates the laser light bonded on top of a silicon waveguide.
The silicon substrate, which is marked in gray at the bottom of Figure3.1, is the base upon which the other items are placed. On this substrate rests the silicon waveguide. Both the substrate and
the waveguide are manufactured using standard silicon fabrication processes.
Both the silicon wafer and the indium phosphide-based wafer are then exposed to oxygen plasma, which leaves a thin coating of oxide on each of the two surfaces that acts as a glue layer. The oxide layer is only 25 atoms thick, yet it is strong enough to bond
the two materials together into a single component.
The oxygen plasma that is used for this layer is similar in concept to the plasma used in fluorescent light bulbs and modern high definition plasma TV screens. Plasma is a gas that has been electrically charged. While fluorescent bulbs are based on plasma that derives from neon or argon gases, the hybrid laser relies on oxygen plasma to coat the components and make them bond. When the silicon and the indium phosphide-based material are heated and pressed together, the two oxide layers fuse them together.
Electrical contacts, (shown as +/- signs in Figure 1) are then patterned onto the device. As shown in Figure 3.2, when a voltage is applied to these contacts, electrons flow from the negative contacts toward the positive contact. When these electrons encounter holes in the semiconductor lattice, they emit a photon (a particle of light). The ability to generate light this way is a property of indium phosphide and other compounds (known as direct band gap semiconductors). Silicon is a poor light emitter because it generates heat, instead of light when electricity is applied”hence the need for the indium phosphide-based material.
As shown in Figure 3.2, the light generated in the indium phosphide based material passes directly through the glue layer into the silicon waveguide below, which acts like the laser cavity to create the hybrid silicon laser. The design of the individual silicon waveguides is critical to determining the performance of the hybrid silicon laser, and will allow future versions to be built that generate specific wavelengths.

Figure3.2 “ Generation of light.
3.2.2 Benefits of hybrid laser
The principal benefit of the hybrid silicon laser is that silicon photonics components no longer need to rely on aligning and attaching discrete lasers to generate light into a silicon photonic chip. In addition, dozens and maybe even hundreds of lasers can be created with a single bonding step. This has several advantages:
¢ The laser is compact so it allows many lasers to be integrated onto a single chip. This first demonstrated hybrid silicon laser is only about 800 microns long. Future generations will be significantly smaller.
¢ Each of these lasers can have a different output wavelength by simply modifying the silicon waveguide properties without having to modify the indium phosphide-based material.
¢ The materials are bonded with no alignment and are manufactured using high-volume, low-cost manufacturing processes.
¢ The laser is easy to integrate with other silicon photonic devices to produce highly integrated silicon photonic chips.
3.3 External Cavity Laser
The simplest type of semiconductor laser is called a Fabry-Perot laser, which generates a beam containing a broad set of wavelengths. To cause the laser to generate only one specific wavelength, the light can be filtered by a grating, which reflects a specific set of wavelengths in a different direction. This design is called an external cavity laser, or ECL. By use of an ECL, the specific wavelengths needed for communication can be individually selected and directed toward other photonic components. (See Figure.3.3)

Figure 3.3 “ A typical ECL setup.
Traditionally, this selection process has required mechanical devices to move the grating as well as the mirrors that direct the wavelengths. This mechanical aspect inherently limited the tuning rate and caused wear on parts. The primary option to avoid these problems was to employ more-expensive lasers that had better wavelength properties. These costly devices do not have moving parts and they create wavelengths with very little spread (that is, most of the light stays close to the fundamental wavelength).
ECL is Fabry-Perot laser with no moving parts. It consisted of an inexpensive laser with a tunable polycrystalline silicon grating embedded in the waveguides”that is, in the silicon channels along which the light waves travel. This filter measured a few microns wide by a couple of millimeters in length. By thermally changing the optical properties of the grating elements, the system could choose a specific wavelength and obtain nearly monochromatic light without reliance on moving parts. This device is important because it enables Intel to use inexpensive
lasers to generate the light and inexpensive silicon filters to improve the wavelength quality to the point that it is suitable for optical communication.
3.4 Continuous Silicon Laser
The generation of photons can be stimulated in many materials, but not silicon due to its material properties. However, an alternate process called the Raman effect can be used to amplify light in silicon and other materials, such as glass fiber. Intel has achieved a research breakthrough by creating an optical device based on the Raman Effect. These devices are built by directing a laser beam “ known as the pump beam “ into a fiber. As the light enters, the photons collide with vibrating atoms in the material and, through the Raman Effect, energy is transferred to photons of longer wavelengths. If a data beam is applied at the appropriate wavelength, it will pick up additional photons. After traveling several kilometers in the fiber, the beam acquires enough energy to cause a significant amplification of the data signal (Figure a). By reflecting light back and forth through the fiber, the repeated action of the Raman Effect can produce a pure laser beam (see sidebar on lasers). However, fiber-based devices using the Raman Effect are limited because they require kilometers of fiber to provide sufficient amplification.

Figure 3.4 “ A typical Continuous Silicon Laser
The Raman Effect is more than 10,000 times stronger in silicon than in glass optical fiber, making silicon an advantageous material. Instead of kilometers of fiber, only centimeters of silicon are required (Figure 1b). By using the Raman Effect and an optical pump beam, silicon can now be used to make useful amplifiers and lasers.

Figure 3.5 “ Differences of using photonics for data transfer.

4.1 Photonics in Processors Manufacturing
Electronic transistors are whittled into silicon wafers to make modern computer chips. However, photons are manipulated using inexpensive computer-generated holograms made of plastic or glass. Photonic computers, therefore, will be far more valuable than their slower electronic counterparts and far less expensive to manufacture.
The hologram technique is leading its way to far more devices on a single chip and this was what every processor and chip manufacturers are looking at. This is even the best suited for the multi core architecture, making it possible to have many processors to be in a single chip. As there is very little heating in these photonic circuits there is less or rather no need for cooling or a heat sink.
4.2 Photonics in Optical Modulators
The simplest method of performing modulation (the process of encoding data on to wavelength of light) is to turn the laser on and off at high speeds. This is direct modulation and has the disadvantage of constantly heating and cooling the laser. Now it is found that Complementary Metal Oxide Semiconductor (CMOS) can be used to modulate light at higher speeds. The transistor like structure can be embedded into a waveguide (the passway through which light travels in silicon).
Rather than turning the laser on and off this silicon modulator uses a technique called phase shifting to encode data by changing the brightness of lightwave. The modulator breaks the light beams into smaller beams. It then makes one of the beams out of phase with those of others and then merges them back. This unified lightwave bears the imprint of both beams and causes the whole beam to go off (Figure).

Figure 4.1 “ Combination of frequencies
This on and off activity is translated into 1â„¢s and 0â„¢s.Thus modulation is achieved by phase shifting as it amplifies the waves at certain points and negates at certain points.(figure)

Figure 4.2 “ A modulator
4.3 Tera scale architecture.
With the demand for speed and bandwidth increasing rapidly we need to switch to more fast devices and here is one Optical transmitter which is a based on this demand.

Figure 4.3 “ Concept of a future integrated terabit silicon optical transmitter.
This figure shows a transmitter containing 25 hybrid silicon lasers, each emitting at a different wavelength, coupled into 25 silicon modulators, all multiplexed together into one output fiber.
Figure shows what a proposed terabit integrated optical transceiver could look like. It consists of a row of small, compact hybrid silicon lasers, each generating laser light at a different wavelength (color). These different wavelengths are then directed into a row of high-speed silicon modulators that encode data onto each of the different laser wavelengths. An optical
Multiplexer would combine these individual data streams together into one output fiber. One of the benefits of optical communications is that all of these signals can be simultaneously sent down a fiber without interfering with each other. If 25 hybrid silicon lasers were integrated with 25 silicon modulators, each running at 40Gbps, the result would be 1 terabit per second of optical data transmitting from a single integrated silicon chip. With this highly integrated silicon photonic transceiver, it is possible to imagine a future world in which most computing devices are endowed with high-bandwidth optical connectivity. Be they servers, desktops, or smaller client devices, all devices will have access to substantially greater bandwidth at a lower cost.
An integrated photonic chip, like the one shown in Figure 3, is expected to play an important role in the Tera-scale Computing, which seeks to leverage multi-core processing by keeping all processor cores as busy as possible. Given the high capacity of these cores and the plans to place 10s to 100s of cores into one future chip, the data demands will be substantial. As a result, tera-scale servers might one day require optical communication to deliver the bandwidth and large volumes of data needed for processing with multiple cores. A key technology for enabling optical communication could be silicon photonics”with the hybrid silicon laser playing a central role.
4.4 Optical Amplifiers
An example of a silicon optical amplifier (SiOA) using the Raman Effect (shown in Figure 4.4). Two beams are coupled into the silicon waveguide. The first is an optical pump, the source of the photons whose energy will cause the Raman Effect. The spectral properties of this pump determine the wavelengths that can be amplified. As the second beam, which contains the data to be amplified, passes through the waveguide, energy is transferred from the pump into the signal beam via the Raman effect. The optical data exits the chip brighter than when it entered; that is, amplified.

Figure 4.4 “ An optical amplifier.
Optical amplifiers such as this are most commonly used to strengthen signals that have become weak after traveling a great distance. Because silicon Raman amplifiers are so compact, they could be integrated directly alongside other silicon photonic components, with a pump laser attached directly to silicon through passive alignment. Since any optical device (such as a modulator) introduces losses, an integrated amplifier could be used to negate these losses. The result could be lossless silicon photonic devices.
4.5 Wavelengths Converters
The Raman Effect could also be used to generate lasers of different wavelengths from a single pump beam. As the pump beam enters the material, the light splits off into different laser cavities with mirrors made from integrated silicon filters (Figure 4.5). The use of lasers at multiple wavelengths is a common way of sending multiple data streams on a single glass fiber. In such a scenario, Intelâ„¢s silicon components could be used to generate the lasers and to encode the data on each wavelength.

Figure 4.5 “ A wavelength converter
5.1 Low prices
The silicon photonics is an attempt to make the silicon based integrated chip (IC) smaller and yet remain efficient. And the goal of the research is not only achieving high performance in silicon photonics, but doing so at a price point that makes the technology a natural fit “ even an automatic feature “ for all devices that consume bandwidth. Thus resulting in cheaper ICs and this is due to the fact that only a small amount of silicon is needed for a photonic computer. And if the level of connections between the components inside the chip is greater then computer generated hologram would bring the solution to this problem.
5.2 Low size
The size of the photonic ICs is very less. By integrating multiple optical functions on a single, easily manufactured, micron-scale photonic crystal chip the size of the devices which use this principle gets more reduced thus making it work for network devices(Optical network), servers which have so many processors.
5.3 More Multi processing.
As the Photonic ICs are ideal for multi core architecture to produce processors with more options fro running more processes, threads in the different processors in the same processor chip, it leads to more level of multiprocessing than is present in our latest processors. As the integration becomes easier and denser in size it increases the efficiency of the computers by providing more cache memory. These kind of systems are ideal for image processing, systems for complex mathematical calculations.
5.4 Less heating
Over heating is the problem that is faced when the processor works more than normal operation speed that is when it is over clocked, but I photonic ICs this is not a problem as they use very less amount of energy and photons which are running inside the ICs for communications are generated by low power laser.
5.5 Parallel computing
It supports parallel computing as the photonic transistors provides pipelined pulses, if the transit time through an electronic transistor is one nanosecond, the input must remain either completely on or completely off for that full nanosecond. Otherwise considerable noise will be introduced into the system. The Photonic transistor, however, is able to operate using pipelined pulses. That is, a continuous stream of very short pulses can be introduced into a single transistor, pulses that are much shorter than the transit time of the device, and they will all be processed independently without any noise buildup.
5.6 Interconnections made easier
Visible-light and IR beams, unlike electric currents, pass through each other without interacting. Several (or many) laser beams can be shone so their paths intersect, but there is no interference among the beams, even when they are confined essentially to two dimensions.

Figure 5.1 “ Connections in electric and optical circuits.
Electric currents must be guided around each other, and this makes three-dimensional wiring are necessary. Thus, an optical computer, besides being much faster than an electronic one, might also be smaller.
Post: #3
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This article is presented by:
Jeremiah K. Jones
English 316
Process Explanation

Photonic Computing


Currently, computers process information in binary units by identifying an electric charge, or the absence thereof, as being a “one” or a “zero.” This allows the computer to calculate at a rate of 2x bpt (bits per unit time), with ‘x’ being the current limit across the system bus. However, the use of Photonic computing could easily increase the rate of computing power to 16x bpt. For example, the current limit for most desktop computers is 32 bpt, so the total output is 2 bpt, or 4,294,967,296 bpt. While that may seems rather fast, the same computer utilizing Photonic Computing Technology would output information at a rate of 16 or 340,282,366,920,938,463,463,374,607,431,770,000,000 bpt. This is 79,228,162,514,264,337,593,543,950,336 times more powerful than most desktop computers.
To accomplish this, an IO device in a Photonic system must first be given a specific light wave frequency range in order to communicate with the CPU (similar to how the Interrupt Request settings work in most PCs). This frequency will allow the computer to know which IO device the incoming information is from. This frequency is further divided into 16 subsequent ranges, each representing a different hexadecimal digit. This allows the device to communicate directly in hexadecimal digits, without needing to translate to binary.

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