Just
about every communication
method from the early telegraph
to today's Internet and television
networks, transmit electrical
signals either by copper
wires or glass fiber optic
cables. Early-on engineers
looked for ways to send more
than one signal through the
wire at the same time. For
example, now over 100 television
channels can be delivered
to your home simultaneously
via a small cable. Movies
and music can be delivered
over the Internet to your
computer. Hundreds of telephone
conversations are handled
simultaneously over a single
fiber optic strand.
One
of the most efficient transmission
media is fiber optics. A single
strand of glass is pulled or
stretched forming pure silicon
into a thread. Light beamed
into one end of the strand
will appear at the other end
just like a copper wire transmits
electrical energy from one
end of a wire to the other.
A number of glass fibers are
usually bundled together in
a cable, each strand able to
carry huge amounts of information.
The total signal carrying capacity
of a wire or a strand of glass
is referred to as "bandwidth" and
the more bandwidth available
the more information can be
carried over it.
Telephones use only about
3500 cycles of bandwidth while
a single TV channel takes about
6,000,000 cycles. The goal
is to cram as many of these
signals as possible through
the fiber optic bundle simultaneously.
To do this engineers have used
lasers as the fiber optic light
source. Lasers can be made
to work in various color ranges.
There are red lasers, green
lasers and recently blue lasers,
and every shade in between.
Each color laser can carry
a large amount of data and
all can be sent over a fiber
optic strand at the same time.
It is relatively easy to use
six, eight or nine lasers at
a time but engineers are striving
to cram hundreds of channels
through a fiber and it gets
tougher to put that many lasers
of different colors together
in a manufacturable package.
If there were a hundred channels,
that would require a hundred
different colored lasers.
The
solution is to make a "tunable" laser.
One single design that can
be tuned to any color via a
software command. That would
allow spare laser replacements
to be built in to circuit boards
and to be tuned to a specific
channel if another laser had
failed. The cost of maintenance
would be negligible compared
with having to send a technician
to replace a single laser and
to have in his inventory hundreds
of lasers of different colors.
Another advantage that telecommunication
carriers hope to see with tunable
lasers is using a circuit board
that is completely configurable
remotely by software. When
traffic patterns change and
more capacity is needed on
certain channels than on others,
signals from the master control
can reassign the channels.
With this capability all the
circuit boards are identical
producing savings on buying
and installing equipment and
they can be configured without
sending out people to install
a new board just to change
the channel configuration.
Tunable lasers are not here
yet, at least in mass production.
Equipment that is designed
to go in boxes that will be
lying on the sea bed or buried
underground have to be proven
extremely reliable. They need
operating lives of decades
since they are so expensive
to install. The outlook so
far is very good although the
technology is very difficult
and complex.
What will this new technology
do for you and me? Sure it
will save the telecommunications
companies millions, but that
allows them to provide more
bandwidth for the capital investment
made. That means making more
bandwidth available in our
homes. It could mean selecting
from thousands of movies over
the Internet and having them
delivered to your television
right then. Not just a pay
per movie to be shown at a
scheduled time as we have now.
It could mean real-time full
motion video gaming shared
by hundreds of people simultaneously.
All playing each other over
the high bandwidth Internet.
It could mean the long sought
goal of telephones with real-time
video displays for everyone.
If you are music fanatic you
could download complete symphonies
or todays top 100 pop tunes
in a few seconds.
I'm
not sure I am ready for all
that stuff. "More" frequently
does not equate to "better".
But, like it or not, tunable
lasers are letting engineers
cram more bandwidth in a cheaper
box. That leaves us to find
out if we will like what they
can deliver.
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