computers that works with light instead of electricity

8/7/2019 Computers That Works With Light Instead of Electricity

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Recently MIT researchers have demonstrated the first

germanium laser that

can produce wavelengths of light useful for opticalcommunication.

the first germanium laser to operate at room temperature.

germanium is easy to incorporate into existing processesfor manufacturing silicon chips.

So the result could prove an important step towardcomputers that move data -- and maybe even performcalculations -- using light instead of electricity.


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As chips computational capacity increases, theyneed higher-bandwidth connections to send data to

memory.

conventional electrical connections will become

impractical.

theyll require too much power to transport data

at ever higher rates.

Transmitting data with lasers

devices that concentrate light into a narrow,

powerful beam.

could be much more power-efficient.


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The lasers used in todays communication systemsare made from expensive materials such as gallium

arsenide, and they have to be constructed

separately and then grafted onto chips, which is

more expensive and time consuming than building

them directly on silicon. Integrating germanium

into the manufacturing process, however, is

something that almost all major chip

manufacturers have already begun to do, since

adding germanium increases the speed of siliconchips.


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How they did it:

In a semiconductor crystal, an excited electron

one thats had energy added to it will break free

and enter the so-called conduction band, where it

can move freely around the crystal. But in fact, an

electron in the conduction band can be in one of twostates.

If its in the first state, and it falls out of the

conduction band, it will release its extra energy

as a photon. If its in the second state, it will release its energy

in other ways, such as heat.


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In direct-band-gap materials, the first state thephoton-emitting state is a lower-energy state

than the second state; in indirect-band-gap

materials, its the other way around. An excited

electron will naturally occupy the lowest-energystate it can find. So in direct-band-gap materials

like gallium arsenide, excited electrons tend to go

into the photon-emitting state; in indirect-band-gap

materials like germanium, they dont.


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The researchers used two strategies to coax excited

germanium electrons into the higher-energy,photon-emitting state.

The first is a technique common in chip

manufacture called doping, in which atoms of

some contaminant are added to a semiconductorcrystal. The group doped its germanium with

phosphorous, which has five outer electrons, where

germanium has only four. The extra electron fills

up the lower-energy state in the conduction band,

causing excited electrons to, effectively, spill overinto the higher-energy, photon-emitting state.


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The second strategy was to lower the energydifference between the two conduction-band

states, so that excited electrons would be

more likely to spill over into the photon-

emitting state. The researchers did that by

straining the germanium or pried its

atoms slightly farther apart than they

would be naturally by growing it directly

on top of a layer of silicon.


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Next steps: The researchers need to find a way to

increase the concentration of phosphorus atoms

in the doped germanium. That should increase

the power efficiency of the lasers, making them

more attractive as sources of light for optical data

connections.


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ADVANTAGES

Increase in the speed of computation.

Immune to electromagnetic interference.

Free from electrical short circuits.

Have low-loss transmission and large bandwidth.

Possess superior storage density and accessibility

No power loss due to excess of heating.


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computers that works with light instead of electricity

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