Robotics Reference
In-Depth Information
processed via logic gates. The main factor limiting the speed of electronic
computers is therefore the speed with which electrons move around in
the silicon chips, which is roughly half the speed of light in a vacuum. 6
In one-billionth of a second (called a nanosecond), light travels a little
under 11.8 inches in a vacuum and approximately six inches through
a silicon microchip, so the lengths of the routes that electrons travel in
silicon chips actually place a limit on the speed of the computational
process because of the time taken for electrons to travel these distances,
even though they are tiny. In other words, computing technology is now
so fast that half the speed of light is not fast enough for the demands that
will be placed on the computers of the future.
Another physical problem that limits computing speeds in silicon is
that reducing the distances and, in particular, the thickness of the silicon
tracks along which the electrons flow, makes them vulnerable to the heat
generated by the flow of electrons. If the tracks are made too thin they
would simply buckle and melt.
Optical computing uses light instead of electrical signals to transport
information (see Figure 58 ) . The optical version of a logic gate is a type
of switch that uses one light beam to control another. The switch is “on”
(corresponding to “true”) when the device transmits light, and “off ” (cor-
responding to “false”) when the device blocks the light. Where electronic
logic gates use electrons as carriers of information, optical logic gates do
so using photons—pulses of light each composed of a minute quantity
of electro-magnetic energy.
The speed of optical logic gates is astounding. Hossin Abdeldayem
and his group at NASA's Marshall Space Flight Center in Huntsville,
Alabama, have developed and tested nanosecond and picosecond opti-
cal switches (a picosecond is one trillionth of a second), which can act
as computer logic gates that perform operations such as addition, sub-
traction and multiplication. The new conducting materials employed
in optical computing allow for the creation of optical switches that are
smaller and 1,000 times faster than silicon transistors. And optical com-
puters will not only be much faster than their electronic predecessors, in
the decades to come they will also be much cheaper and much smaller.
Optical computing is already a huge growth industry, even though
the day of the first all-optical computer is probably decades away.
6 Light travels faster in a vacuum (approximately 186,000 miles per second ) than it does through
air, or through other gases, liquids or solids. One of the conclusions of Albert Einstein's research is
that it is impossible for anything to travel faster than the speed of light.
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