The Evolution of Fiber Optic
The Evolution of Fiber Optic
Communications
Communications
WHAT IS OPTICAL FIBER?
WHAT IS OPTICAL FIBER?
An optical fiber (or optical fibre) is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair
What is purpose of optical
What is purpose of optical
fiber?
fiber?
It is basically used to transmit signal information in the form of light
Early Optical Communications
Early Optical Communications
The French used semaphores to The French used semaphores to
transmit messages in the 1790s
transmit messages in the 1790s
Later systems also sent optical Later systems also sent optical
signals through the air
signals through the air
• But clouds, rain, and other atmospheric But clouds, rain, and other atmospheric
disturbances can disrupt optical signals
disturbances can disrupt optical signals
sent through the air
sent through the air
Guiding Light With Water
Guiding Light With Water
Light in a stream of Light in a stream of water stays inside
water stays inside
the water and bends
the water and bends
with it
with it
This was first This was first
demonstrated by
demonstrated by
Daniel Collodon and
Daniel Collodon and
Jacques Babinet in
Jacques Babinet in
the 1840s
Total Internal Reflection
Total Internal Reflection
There is a critical angle at There is a critical angle at
which no light can be
which no light can be
refracted at all, so 100% of
refracted at all, so 100% of
the light is reflected
the light is reflected
• Light is trapped in the water Light is trapped in the water and cannot escape into the
and cannot escape into the
air
air
• This works with any dense This works with any dense medium, such as plastic or
medium, such as plastic or
glass, the same way it works
glass, the same way it works
with water
How Light Travels in Fiber
How Light Travels in Fiber
Bare Fiber
Bare Fiber
During 1920-1950, During 1920-1950,
thin, flexible rods of
thin, flexible rods of
glass or plastic
glass or plastic
were used to guide
were used to guide
light
Fiber With Cladding
Fiber With Cladding
Developed in 1954 Developed in 1954
by van Heel, Hopkins
by van Heel, Hopkins
& Kapany
& Kapany
Cladding is a glass or Cladding is a glass or
plastic cover around
plastic cover around
the core
the core
Protects the total-Protects the
total-reflection surface
reflection surface
contamination
contamination
Reduces cross-talk Reduces cross-talk
from fibers in
from fibers in
bundles
Medical Imaging
Medical Imaging
By 1960, glass-clad fibers were By 1960, glass-clad fibers were
available for medical instruments, to
available for medical instruments, to
look inside the body
look inside the body
The glass was unable to transmit The glass was unable to transmit
light far enough for communications,
light far enough for communications,
because of impurities
because of impurities
• Attenuation (loss of light) was 1 decibel Attenuation (loss of light) was 1 decibel per meter
Decibels
Decibels
Decibels are a logarithmic scale of powerDecibels are a logarithmic scale of power • Abbreviated dBAbbreviated dB
A loss of 10 decibels means only 10% of A loss of 10 decibels means only 10% of
the light gets through
the light gets through
A loss of 20 dB means 1% of the light gets A loss of 20 dB means 1% of the light gets
through
through
• Sunglasses stop 99% of light, so they cause a Sunglasses stop 99% of light, so they cause a loss of 20 dB
loss of 20 dB
For communications, loss must be no more For communications, loss must be no more
than 10 or 20 decibels per kilometer
Optical Fiber in 1966
Optical Fiber in 1966
Charles Kao developed a fiber that Charles Kao developed a fiber that
could transmit (One billion bits per
could transmit (One billion bits per
second)
second)
But attenuation was 1000 dB/km, so But attenuation was 1000 dB/km, so
it could not transmit light far enough
it could not transmit light far enough
for practical communications
scientists developed
scientists developed
low-attenuation silica glass fibers in
attenuation silica glass fibers in
1970
1970
Optical Fiber in 1977
Optical Fiber in 1977
Telephone signals used infrared light Telephone signals used infrared light
with a wavelength of 850 nm to send
with a wavelength of 850 nm to send
data at 6.2 Mbps and 45 Mbps
data at 6.2 Mbps and 45 Mbps
Loss was 2 dB per kmLoss was 2 dB per km
Repeaters were required every few Repeaters were required every few
kilometers
kilometers
• The repeaters were electro-optical – The repeaters were electro-optical – converting the light to electricity and
converting the light to electricity and
then back to light
Fiber Optics History
Fiber Optics History
First installed in Chicago in 1976First installed in Chicago in 1976
By the early 1980s, fiber networks By the early 1980s, fiber networks
connected the major cities on each
connected the major cities on each
coast.
The 1980s
The 1980s
By the mid-80s, fiber was replacing By the mid-80s, fiber was replacing
all the telco copper, microwave and
all the telco copper, microwave and
satellite links
satellite links
In the 90s, CATV started using fiber In the 90s, CATV started using fiber
to enhance the reliability of their
to enhance the reliability of their
networks
networks
• CATV companies also discovered they CATV companies also discovered they could offer phone and Internet service
could offer phone and Internet service
on that same fiber and greatly enlarged
on that same fiber and greatly enlarged
their markets
