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Monday, July 18, 2016

Fiber optics: Information 'packed into light'

by Mark Ollig

Copyright © 2016 Mark Ollig

The ability to guide light in other than a straight line was demonstrated in 1841.
Jean-Daniel Colladon, a Swiss physicist, showed how a ray of light, traveling inside a curved arc of flowing water would bend, thus becoming “refracted.”
He called this event “light guiding.”
It was; “one of the most beautiful and most curious experiments that one can perform in a course on optics,” Colladon later wrote.
Jumping ahead 135 years, we find engineers have successfully sent and received information over a beam of light.
This was accomplished by having the light encode the information to be transmitted, using direct modulation via multiplexing laser frequencies within the modulated light, guided through a transparent, fiber-optic glass strand.
The “laser” acronym means: Light Amplification by Stimulated Emission of Radiation.
“It is a device which produces light. Tunable lasers can produce light of a single frequency, or visible color, in human terms. By turning the laser light signal on and off quickly, you can transmit the ones and zeros of a digital communications channel,” is the description of a laser from my trusty Newton’s Telecom Dictionary.
The two most common light sources for fiber-optic transmission are: LED’s (light-emitting diodes), and laser diodes.
In 1976, information encoded within laser light was successfully sent over a fiber-optic telephone cable installed at AT&T’s research facility in Atlanta, GA.
During the same year, the copper wiring harness from an A-7 Corsair US military fighter jet was replaced with a fiber optical link network.
This optical link contained 250 feet, consisting of 13 fiber-optic cables, weighing 3.75 pounds
The A-7 Corsairs’ previous copper wiring harness was comprised of 300 individual copper wire circuits, totaling 4,133 feet, and weighing 88 pounds.
Today’s fiber optics installed in modern aircraft, allows military pilots to make instantaneous decisions using high-resolution imaging systems, displays, and flight controls linked with fiber optic networks providing real-time data.
In 1977, AT&T’s first commercial application of transmitting communications over a fiber-optic cable took place in Chicago.
Unbeknownst to the public, certain fiber-optic technologies were stealthily being used in the 1960s.
Your investigative columnist did some digging.
I discovered NASA’s black- and-white lunar television camera, used by the Apollo 11 astronauts on the surface of the moon in 1969, incorporated fiber-optic technology.
The use of fiber-optic technology in the lunar television camera was considered “classified CONFIDENTIAL” in NASA’s “Lunar Television Camera Pre-installation Acceptance (PIA) Test Plan” document 28-105, dated March 12, 1968.
This Apollo 11 lunar surface camera was kept inside a storage compartment on the descent stage of the lunar module “Eagle.”
Westinghouse Electric Corporation’s Aerospace Division developed and manufactured the Apollo Lunar Television Camera (part number 607R962).
The original lunar television camera remains on the surface of the moon, in the Sea of Tranquility, near the Apollo 11 landing site.
But I digress from today’s topic.
We had previously believed fiber-optic technology would not reach its data-capability bandwidth ceiling for many years to come; however, this is no longer the case.
According to the University of the Witwatersrand, Johannesburg, South Africa, the increases in amounts of data being used, coupled with the advances in information technology, are going to have troublesome repercussions on the current technology used for providing the bandwidth needed to transport data – even over fiber optics.
“Traditional optical communication systems modulate the amplitude, phase, polarization, color, and frequency of the light that is transmitted,” the news release from the University stated.
Researchers from this university began working with the South Africa’s Council for Scientific and Industrial Research.
They demonstrated how over 100 separate light patterns (representing data) could be individually sourced through a single optical communications link.
The researchers created a computer hologram encoded with over 100 light pattern configurations in multiple colors.
These light pattern configurations were sent through an engineered liquid crystal, which acted as a single spatial light modulator.
As this single light was transmitted, each individual light pattern was “demultiplexed,” meaning, the 100 individual light configuration patterns were extracted and sent to their unique designated locations.
All 100 light patterns were detected simultaneously.
This test was performed in a laboratory; the next stage involves demonstrating this new technology in a “real-world” situation.
This increase in light patterns will allow for a huge expansion in available bandwidth used for the transmission of voice, video, and other data.
The additional bandwidth availability will result in information being more efficiently “packed into light.”
Back in the day, this old telephone cable splicer used to worry about having enough copper pairs to handle voice traffic.
Today, with fiber optics, we’re worried about having enough light to handle data bandwidth requirements.
Go figure.
To see the March 12, 1968, NASA booklet describing the “Lunar Television Camera,” go to:
In this booklet, Section 1.1 “Security Classification” includes the “classified CONFIDENTIAL” portion of the fiber optics used with the lunar television camera.

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