| There is a new fiber optic data transmission scheme that utilizes something
called Soliton Pulses. These are very
short bursts of light generated in an Erbium-doped Fiber LASER. Soliton
light can be used to transmit data at rates in excess of 50 Gb/s, at distances
over 19,000 km of Dispersion-Shifted Fiber, requiring no repeaters,
and with no errors. This data rate is the equivalent of sending 6,200 bibles
per second. At this rate, one bible could be sent to everyone on earth--5.5
9
people--in
about 10 days.
In the case of repeaters, in a long-haul fiber: instead of converting
the light into electrical signals, amplifying, correcting errors, retiming
and retransmitting light pulses, an optical amplifier is used. It consists
of about 30 meters of Erbium-doped fiber, assorted filters and beam splitters,
and pumped by a 15 mW LASER diode operating at 1550 nm. This arrangement
adds about 30 dB of gain with no appreciable noise. Also, the bandwidth
of this amplifier is on the order of 40 THz. At this rate, one bible could
be sent to everyone on earth, 5.5 9 people, in about 18 minutes.
The Shortest LASER pulse, to date, is ~10 Femtoseconds (10 -15
sec).
Light would travel 1/8th the thickness of a sheet of paper in that time.
10 Fsec is to one second as one second is to 3.2 million years. |
| A Soliton Pulse is: a pulse
of light--of sufficient intensity and correct wavelength --traveling down
a special non-linear optical fiber known as, Dispersion-Shifted Fiber,
is classified as a Soliton Pulse. This Soliton light pulse exhibits a unique
characteristic of getting shorter--not longer, as conventional wisdom would
dictate. Due to the non-linearly of the fiber in the presents of light
exceeding some quantum threshold of intensity--the leading edge of the
pulse is being overtaken by the faster trailing edge. That is, the leading
edge of the light is undergoing a Doppler Red-Shift,
while the trailing edge is experiencing a Doppler Blue-Shift.
The result of this effect is a shortening of the pulse duration, with a
corresponding increasing Peak Power.
As the pulse looses energy (joules) over distance, it increases in Peak
power--thus insuring itself's staying above the peak threshold of the fiber
needed for the phenomenon in the first place! |
