A new type of plastic cable developed in Japan could flood individual homes with information
IN Tins age of information, telecommunications is evolving at a breakneck
pace. While a few years ago, even movie channel through a TV cable was
something of a novelty, the technological pundits are today close to realising
their vision of sending 500 cable channels into each home, simultaneously.
Though this was possible using high
performance glass 6bre-optic cables
capable of transmitting massive
amounts of data in the form of pulses of
light, the cost of taking these fibres from
the curb to each house was a prohibitive
factor. Now, a group of Japanese researchers say that they have developed a new
type of plastic cable that would be
cheaper than glass optical fibres and yet
be capable of transmitting huge
amounts of data over short distances
(Science, Vol 267, No 5206).
Glass fibre-optic cables are poorly
suited for 'short-hop' application. Each
is thinner than a hair, and expensive
junction equipment is required to align
the optical beam so that it carrjump
from one 'trunk' fibre to another.
In contrast, the copper wires that are
conventionally used for cable TV are
cheap andsimple but they cannot transmit nearly as much data as the fibres do.
The solution can be found in one word:
plastics, say researchers -
from the Kcio Univer- Highest sity in Yokohama.
Led by material sci- Graded-index
entist Yashuhim Koike, more information
the team of researchers copper wire
has devised a new type
of plastic optical fibre Carrier
to transmit light pulses
from a red semiconductor laser at a blinding Copper wire
2.5 billion bits per sec- Step-index plastic
ond - that's a transmission rate, or hand-width, 25 times greater than that of a
copper cable.
"The performance is more than
enough to handle the transmission
demands of most short-hop applications for the foreseeable future," says
Robert Steele, a plastic-fibre specialist
with Delphi gackard Electric in Warren,
Ohio. Plastic-optical fibres have been in
use for over a decade now for wiring homes and also for carrying information between sensors and processors in robots.
But the traditional plastic fibres -
known as step-index fibres - were not
suitable for high speed transmission of
data. Reason: Photons in each light
pulse travelling down the fibre spread
apart as they move. As a result the pulses, which constitute the signals, must be spaced far apart or they overlap. That
limits bandwidth to 100 million bits per
second over 100 metres of fibre.
This problem, however, does not
afflict normal glass fibres because their
extremely narrow confines ensure that
photons travel only in one path.
The fibre developed
by Koike and his colLeagues is what is called
a graded-index fibre,
OUW which sharply reduces
pube the scattering of signals
(we diagrarn). The fibre
consists of polymethyl
methacrylate (PMMA)
a common fibre polymer - with continuously graded concentrations of some highly
refractive dopants
molecules which when
added to the solid PMMA
fibre help reduce scattering of light pulses.
The researchers, however, concede
that the new fibre does not dispense
with the degradation problem altogether. "Optical signals still get knocked
down by a factor of around 30 after they
pass through 100 metres of the fibre,"
says-Harry Lockwood, an opto-electronic consultant with the Lockwood
group in Newton, Massachussetts. 'But
it's still usable, because 100 metres is
ample for wiring most homes or local
Computer networks within offices," he adds.
Highest
grade Graded-index plastic fibre can carry 25 times more information than the conventional copper wire |
|
Carrier | Bandwidth over 100
m (Megabits per second) |
Copper wire | 100 |
Step-index plastic fibre | 100 |
Granded-index plastic fibre | 2500 |
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