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Optical Computer is indeed the computer technology of future which uses light particles called Photons. This post will discuss Optical Computer, Optical Components required for computation, why we need it, its working principle, advantages and disadvantages.

What is an Optical Computer

A device that uses Photons or Infrared beams, instead of electric current, for its digital computations is termed as an Photonic or Optical Computer.

The flow of electric current is only 10 percent of the speed of light. This poses severe restrictions on long distance data transmission. Such restrictions resulted in the evolution of optical fiber. By applying the advantages of IR networks and/or visible light at the component and device scale, a computer (Optical Computer) can be developed that has 10 times more processing power than conventional systems.

Prototype of Optical Computer

Fig. 1 – Prototype of Optical Computer

Unlike electric current, IR beams and visible light can pass through each other without interaction. Several laser beams can be projected so as to intersect their path, but the beams will have no interference even when they are confined to two dimensions.

With electric currents, three dimensional wiring becomes necessary since they have to be guided around each other. Thus an Optical Computer, apart from being faster, can also be smaller. Figure 2 below shows an 8 bit or Bit-Serial Optical Computer.

First 8 - Bit Optical Computer

Fig. 2 – Bit-Serial Optical Computer

Main Optical Components in Optical Computer

The main Optical components required for computing in an Optical Computer are:

  • VCSEL (Vertical Cavity Surface Emitting Micro Laser)
  • Spatial Light Modulators
  • Optical Logical Gates
  • Smart Pixels

VCSEL (Vertical Cavity Surface Emitting Micro Laser)

VCSEL is a semiconductor Micro Laser Diode that emits light vertically from the surface. It basically converts the Electrical Signal to Optical Signal. It is the best example of one dimensional Photonic Crystal.

Spatial Light Modulators

Spatial Light Modulators are responsible for modulating the intensity and the phase of the Optical beam. They are used in Holographic Data Storage systems as they encode the information into a laser beam.

Optical Logic Gates

An Optical Logic Gate is nothing but an Optical Switch that controls the light beams. It is said to be “ON” when the device transmits light and “OFF” when the device blocks the light.

Smart Pixels

Smart Pixels help Optical Systems with high levels of Electronic Signal Processing.

Why do we need Optical Computer

The need for Optical Computer (s) emerged from the fact that the conventional computers are limited by the time response of electronic circuits and also the building up of heat damages the electronic components. For example: Microprocessors contain billions of transistors and sometimes they operate at clock speeds in excess of 3 billion cycles per second which implies that the transistors are exposed to lots of heat, which accelerates their chances of damage.

The other factors which adds to this need of developing a better alternate are:

  • The End of Electron Based Computing as Moore’s Law is Failing
  • A plateau in Computer Processing Chips

The End of Electron Based Computing as Moore’s Law is Failing

Computers work with zeros and ones. Little switches called transistors make this possible and there are billions of them found on current Integrated Circuits and Processor Chips. In 1965, the founder of Intel, Gordon Moore, predicted that there would be a doubling in the number of transistors on every chip, every two years. This came to be popular as Moore’s law.

This prediction was accurate up to the beginning of the 21st century. While the predicted exponential growth has not completely stopped, it has certainly slowed down. Transistors are now being manufactured in atomic sizes. This implies that there will soon be bottlenecks in the quantum mechanical effects.

Current or electrons can disappear randomly from these minute electrical components, thereby resulting in incorrect calculations. Also, the latest technology where transistors measure only five nano meters has become very complex and too expensive to advance.

A Plateau in Computer Processing Chips

A closer inspection reveals that there has been a decline in the performance of transistors. Looking back, we realize that faster computers were bombarding the market every few years. Today, however, computers are stuck at 4 GHz speed. Yet, it is possible to improve performance with smart chips and parallel processing. However, this increase in speed is attributed not only to transistors but also to various other circuitry.

Optical Transistors

Fig. 3 – Optical Transistors in Optical Computer

All these benefits incur a cost. Processor cores need to constantly maintain communication which consumes energy. It is so high that communication between the chips is known to consume more than half of the total computing power. Since computers are in our smart phones, laptops, internet and data centers, this energy consumption leaves behind a substantial amount of carbon footprint.

Working Principle of Optical Computer

The working principle of Optical Computer is similar to the conventional computer except with some portions that performs functional operations in Optical mode. Photons are generated by LED’s, lasers and a variety of other devices. They can be used for encoding the data similar to electrons.

Design and implementation of Optical transistors is currently under progress with the ultimate aim of building Optical Computer. Multi design Optical transistors are being experimented with. A ninety degree rotating, polarizing screen can effectively block a light beam. Optical transistors are also made from dielectric materials that have the potential to act as polarizers. Optical logic gates are slightly challenging, but fundamentally possible. They would involve one control and multiple beams that would provide a correct logical output.

Optical Network and Photonic Chip

Fig. 4 – (a) Optical Network on Chip (b) Photonic Chip on Circuit

Electrons have one superior advantage in that, silicon channels and copper wires can be turned and electrons would follow. This effect can be emulated in Optical Chips using Plasmonic Nano particles. They are used for turning corners and continue on their path without major power loss or electron conversions.

Most parts of an Optical chip resembles any other commercially found computer chip. Electrons are deployed in the parts that transform or process information. The interconnects however, have drastic changes. These interconnects are used for information shuttling between different chip areas. Instead of electron shuttling, which might slow down when interconnects heat up, light is shuttled. This is because light can be easily contained and has an advantage of less information loss during travel.

Researchers are hoping that this swift communication process might result in the development of exascale computers i.e. computers that perform billions of calculations every second, 1000 times more processing speed than current speediest systems.

Advantages of Optical Computer

The advantages of Optical Computer are:

  • Optical computer has several major advantages of high density, small size, low junction heating, high speed, dynamically scalable and reconfigurable into smaller/ larger networks/ topologies, massive parallel computing ability and AI applications.
  • Apart from speed, Optical interconnections have several advantages. They are impervious to electromagnetic interference and are not prone to electrical short circuits.
  • They offer low-loss transmission and large bandwidth for parallel communication of several channels.
  • Optical processing of data is inexpensive and much easier than the processing done on electronic components.
  • Since photons are not charged, they do not readily interact with one another as electrons. This adds another advantage in that, light beams pass through each other in full duplex operation.
  • Optical materials have greater accessibility and storage density than magnetic materials.

Disadvantages of Optical Computer

The disadvantages of Optical Computer are:

  • Manufacturing Photonic Crystals is challenging.
  • Computation is complex as it involves interaction of multiple signals.
  • Bulky in size.

Future of Optical Computing

We can see interesting developments in lasers and lights. These are taking over the electronics in our computers. Optical technology is currently being promoted for use in parallel processing, storage area networks, Optical Data Networks, Optical Switches, Biometric and Holographic storage devices at airports.

Processors now contain light detectors and tiny lasers that facilitate data transmission through Optical Fiber. Few companies are even developing Optical Processors that use Optical Switches and laser light to do the calculations. One of the foremost promoters ‘Intel’ is creating an Integrated Silicon Photonics link that is capable of transmitting 50 Gigabytes per second of uninterrupted information.

It is speculated that future computers would come without screens where information presentation is made through a hologram, in the air, and above the keyboard. This kind of technology is being made possible by the collaboration of researchers and industrial experts. Also, Optical technology’s most practical use i.e. the ‘Optical Networking business’ is predicted to reach 3.5 billion dollars from 1 billion currently.

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