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Optical Fibers:
Communicating Faster, Farther, and Better
Abstract
We live in a world that is more connected now than ever before. The internet
influences all facets of our lives and plays a critical role in today’s society.
Unfortunately, the internet is growing much faster than the infrastructure we have
supporting it. In order to keep up with the surging demand, we must upgrade our
infrastructure. Optical fibers are a cost-effective and versatile solution that will
provide reliable internet for many years to come.
Key Words
Fiber Optics
Internet
Bandwidth
Prepared by Henry Li
Author Biography
Henry is a junior studying Biophysics.
Contact Information
henryli@usc.edu
Paper Submitted December 7, 2012
Prepared for
Marc Aubertin, Professor Writing 340 (66800)
USC Viterbi School of Engineering
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We live in a connected world where physical distances no longer restrict our ability to
communicate with others. In many ways, digital communication has revolutionized the way we
interact with others. Today, most telecommunication networks use copper cabling in their
infrastructure. While effective, copper wiring is quickly becoming obsolete. The exponential
growth of the internet has contributed to a dramatic increase in the demand for bandwidth. With
copper’s limited bandwidth capacity, telecommunication networks are quickly being pushed to
their limits. Because of this, delays and outages are becoming increasingly common. Even
though delays of a few seconds may not sound like much, they can place additional strain onto
an already overloaded network. In order to ensure the long-term reliability and sustainability of
our networks, the telecommunication industry is transitioning away from copper and towards
optical fibers. The transition towards optical fibers will improve upon our existing infrastructure
and increase access to faster, higher quality, and more reliable data networks that will meet our
bandwidth demands for many years to come.
Even though fiber optics is used extensively in modern society, it is relatively simple and
old technology. Fiber optics is possible because of light’s ability to undergo total internal
reflection. Total internal reflection occurs when light rays are unable to escape from the medium
that they are traveling in. In our case, the transmitted light is contained within a flexible and
transparent fiber made from a glass and silica composite. The optical fiber essentially functions
as a “light tube” that transports light pulses from one end of the fiber to the other. Even though
this property was discovered in the 1840’s, 130 years passed before the first true optical fiber
was developed. [1]
After the initial discovery in 1840, early experiments focused on bending light through a
water stream. Unfortunately, there were no practical applications for this technology at the time.
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In 1880, Alexander Graham Bell invented the photophone, a device that sent sound through a
light beam. Even though this represented a major step towards an advanced form of
telecommunication, static interference and high attenuation1, or signal loss, made this technology
impractical. In the mid 1960’s, German physicists demonstrated the first optical transmission
system. They were able to send laser pulses through a glass tube, but they were losing 99% of the
light (data) in the process. Their experiment was significant because they demonstrated that pure
silica glass was the only suitable transmission medium for light. The first practical optical fiber
came in 1970 when American scientists developed a fiber2 capable of retaining and amplifying
an electrical signal. This ushered in a new era of telecommunications and advances in the field of
fiber optics grew at an exponential rate
Figure 1 – Total Internal Reflection
This demonstrates the basic principle behind total internal reflection. Note that the two light waves are
always reflected back when they reach the medium boundary. Optical fibers take advantage of this
principle to direct light pulses in a forward direction without losses. Furthermore, simultaneous light
pulses can also be transmitted through a single fiber. Image courtesy of howstuffworks.com.3
So how can light pulses transmit data? To answer this question, we have to understand
what data is. Data is digital information that a computer can interpret and analyze. This digital
1
An attenuation threshold of 20dB/km represents a pratical communication medium. This value represents data loss.
Too much data loss and the transmission will be incomprehensible. Bell’s device had a loss 200x this value.
2
This fiber had an attenuation of 17dB/km. Later, they lowered it to 10dB/km by infusing quartz into the silica.
3
Image obtained from an article on How Fiber Optics Work. http://computer.howstuffworks.com/fiber-optic2.htm
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information is in a binary form, where data is represented by a series of 0’s and 1’s. In fiber
optics, an optical transmitter encodes the digital information into an optical signal. The optical
signal uses light pulses, or a lack thereof, to represent the signal. For instance, the presence of a
light pulse represents a 1 and no light pulse represents a 0. [2] After traveling the length of the
fiber, the light pulses reach an optical receiver that encodes the data back into a digital signal. It
is important to note that the optical receiver is detecting the changes in light energy rather than
the individual light pulses. When light hits the receiver, it is converted into heat energy which the
detector measures. Even though modern fibers are much more complex, these are the basic
principles behind this technology. Interestingly enough, the use of light as the signal carrier
offers several major advantages over that of electrical signals in traditional copper wiring.
One of fiber’s most significant advantages is its high data carrying capacity. Compared to
copper, fiber can transmit more data over longer distances. According to Robert Malaney, an
electrical engineering professor at the University of New South Wales in Australia, a local area
network (LAN) constructed from fiber can carry over 31,000 simultaneous phone calls whereas a
LAN built using copper can only carry 3,000. [3] This advantage means that one optical fiber can
essentially replace ten copper cables. In addition to lower costs, fiber can also reduce clutter and
streamline networks. Because of its high carrying capacity, optical fibers are more efficient and
faster than copper wiring. However, what exactly does “faster” mean?
Different transmission channels have different throughput rates4, or “speeds.” Even
though light pulses in fiber travel very close to the speed of light, this is not important when
considering the advantages of fiber. The difference between this and that of electric signals in
copper wiring is almost insignificant. Because optical fibers have a larger capacity, it takes less
time to transmit a certain amount of data over long distances. A good analogy for this would be
4
The average amount of successful transmissions per unit time measured in bits/second.
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the use of two pipes, one with a diameter ten times larger than that of the other, to transport the
same amount of water. Even though the water moves with the same velocity in both pipes, the
larger diameter pipe can hold and transport more water at any given time. Consequently, the
larger pipe takes less time to move all of the water. In this sense, the large pipe is “faster” than
the small pipe. Optical fibers are analogous to the large diameter pipe and its inherent speed is
one advantage that allows it to have a wide range of applications.
Even though fiber’s inherent speed is important, we must also consider the quality of the
transmitted signal. Packet loss5 is one of the most frustrating issues in digital communication
because it lowers performance and negatively affects quality of service. When there is heavy
network traffic, the entire network will slow to a crawl. At this point, the network will either
prioritize data transmission or crash. Packet loss occurs when the network has to prioritize which
data packets to transmit. Unfortunately, individual data packets are indistinguishable from one
another. As a result, some, but not all, of the packets that make up a transmission will eventually
make it to the end. The others will be “lost,” hence the name packet loss. As an example, the loss
of data packets corresponding to a video will cause pixilation. Fortunately, optical fibers are able
to maintain the clarity and the quality of their signals, especially during periods of heavy network
traffic. One reason for this is the fact that fiber experiences much less external interference than
copper wiring because photons, rather than electrons, are the signal carrier.
Compared to signals in optical fibers, the electrical signals in copper wiring are more
susceptible to electromagnetic interference (or EMI). [4] EMI occurs when electronics are
exposed to electric and magnetic fields. This exposure results in a disturbance that may interfere
with transmitted signals. For instance, an underground power line may cause EMI in a copper
communications cable if the two cables are in close proximity. The charged power line creates an
5
Packets are formatted units of data that can be transmitted.
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electromagnetic (EM) field that can penetrate the copper cable. [5] This leads to interference
because the copper cable misinterprets the external EM as a signal coming from within itself.
Because of this, the legitimate signals are slightly weakened. Although copper and fiber cables
both have shielding of some sort, the fiber has an additional layer of protection. The silica in
optical fibers is a dielectric that insulates the cable from EMI. Because of this, the original signal
remains unaffected. In short, optical fibers have additional layers of protection, above and
beyond those found in copper wiring, that ensure reliability and security.
Up until now, we have only discussed the advantages of optical fibers. However, it is
important to note copper may be a more suitable choice in some cases. Although the cost of fiber
has declined in recent years, it takes considerable time and effort to install the necessary
equipment. [6] Most households will not take full advantage of a fiber’s benefits because they do
not run bandwidth-intensive services. In other words, copper wiring is good enough for their
needs. Because home networks cover short distances, EMI is not a factor. Likewise, speed
differences are also insignificant over these distances. Under these circumstances, the benefits of
fiber are diminished to such a point where copper wiring may be the more cost efficient option.
Again, this can apply to most, but not all, households. For now let us go above household level
and examine a situation where optical fibers have a clear advantage.
Because we live in a global society, international telecommunication is more important
now than ever before. This is made possible in part by submarine communication cables that line
the sea floor. In many respects, these cables figuratively and literally connect the world together.
They carry 95% of all international data traffic and nearly all transoceanic internet traffic. [7]
Constructed from optical fibers, these cables, a few feet in diameter, are resilient, fast, and
reliable. Despite their small size, they have incredible capacities. For instance, the SAm-1 (South
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America – 1) cable has an overall capacity of 480 GB/s. To put this into perspective, this cable
sends and receives data two million times faster and more efficiently than the average U.S.
household. According to the International Cable Protection Committee, SAm-1 and eight oceanic
cables combine to handle all of South America’s internet traffic (Figure 2). On top of this, these
cables are operating at no more than half of their maximum capacity. There is so much available
bandwidth that these cables can actually encourage the growth of the internet in South America.
In many ways, these cables are the unsung heroes of the internet. The exponential growth of the
internet is due in a large part to the development and implementation of fiber optic technology.
Figure 2 – Submarine Telecommunication Cables for South America
The cables indicated here handle all international traffic for South America. The SAm-1 cable is
highlighted in red. Image has been cropped for clarity. Image courtesy of the International Cable
Protection Committee (IPCC).6
In addition to its impact on international telecommunication, fiber also has a large impact
in the domestic arena. With the growth of the internet, services that have traditionally been
offered as a stand-alone product are now being offered through the internet. People are
transitioning away from landlines and cable TV and towards VoIP and video-on-demand.
6
Image taken from IPCC’s interactive submarine cable map. http://www.iscpc.org/
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Although convenient, these services require a tremendous amount of bandwidth. In order to meet
this demand, internet service providers are using fiber to upgrade their existing infrastructure.
The different configurations for implementing fiber are collectively known as “fiber to
the x,” where the x indicates the termination point of fiber. [8] As shown in Figure 3, these
configurations use fiber initially and then switch to metallic cables at some point. We will be
focusing on two configurations, fiber to the node (FTTN) and fiber to the home (FTTH), that are
the most widely implemented at the consumer level.
Figure 3 – Diagram of “fiber to the x” configurations, not drawn to scale.
The buildings on the left represent the service provider’s central office and the buildings on the right
represent the end-users. Note the heavy fiber penetration for the FTTH configuration, as compared to
FTTN. The two variants in the middle are fiber to the cabinet (FTTC) and fiber to the basement (FTTB).7
As we have previously mentioned, the benefits of fiber are heavily diminished when
implemented on a small scale. By implementing fiber on a much larger scale, the advantages of
fiber are more apparent. In a FTTN configuration, the optical fibers terminate at a street cabinet,
or node, that serves each neighborhood. Because the optical fibers terminate at the cabinet,
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Image provided by Wikimedia, under the Creative Commons license. http://en.wikipedia.org/wiki/File:FTTX.png
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households in the community can keep their existing copper installation and can still benefit
fiber’s increased reliability. This is important because FTTN allows for the rapid deployment of
fiber across an entire region and at a lower cost for the internet provider. The major drawback to
FTTN is the fact that the network’s throughput is limited by the copper cabling at the terminal
end. For households with low bandwidth needs, this will not be a problem. However, this does
have an impact on those households or small businesses that need the extra bandwidth. For this,
we need to look at the benefits of a fiber to the home (FTTH) configuration.
In a FTTH configuration, fiber runs from the central office directly to individual homes.
This configuration maximizes the use of optical fibers and minimizes the use of copper wiring.
Because of this, FTTH is no longer limited by copper and higher speeds are possible. In many
ways, FTTH is the only solution for consumers who require a lot of bandwidth. For instance,
small businesses with an active internet presence need the reliability and dependability that
FTTH provides. Adding to this, their servers might need the extra bandwidth to accommodate for
incoming traffic. In short, fiber is a must have for those who depend on a fast and reliable
internet connection.
Our world is more connected now more than it has ever been. We can communicate and
interact with people across the globe and not think for a second as to how amazing that really is.
In many ways, this is all possible because of optical fibers. These tiny glass tubes, no more than
a few millimeters thick, enabled the internet’s exponential growth and radically changed the
world that we live in. As the internet continues to grow, so will the applications that drive it. And
with optical fibers we will no longer be limited by the networks that we are connected to. In
many ways, optical fibers represent just how far we have pushed the limits of technology. Just
imagine what will be possible in a few years; the possibilities are endless.
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Bibliography
[1] Royal Swedish Academy of Sciences, "The Nobel Prize in Physics 2009," Royal Swedish
Academy of Sciences, 2009. [Online]. Available:
http://www.nobelprize.org/nobel_prizes/physics/laureates/2009/kao.html.

This article describes Dr. Kao's early research in optical fibers. It also provided
insight into into the difficulites faced by reseachers during the early years of optical
fibers. It was very challenging to engineer composite materials that would be able to
transmit the light pulses with as few losses as possible. Dr. Kao eventually settled on
a glass-silica composite, which is very similar to what we use today. Fortunately,
this article focused on Dr.Kao's work as much as it did on himself.
[2] phys.org, "Fiber-optic network sets world record," phys.org, 28 March 2006. [Online].
Available: http://phys.org/news62776076.html. [Accessed October 2012].

There was a specific paragraph in this article that described how light pulses
simulate data when in a fiber optic cable. It mentioned binary and its role in
encoding data into a digital format. This was a very helpful article that helped me
explain exactly how light can trasmit data.
[3] R. Malaney, "Why is fibre optic technology 'faster' than copper?," 21 October 2010.
[Online]. Available: http://www.abc.net.au/science/articles/2010/10/21/3044463.htm.

This article documented an interview of Professor Robert Malaney. Malaney is an
expert on fiber optics. He offered key insight into physical mechanisms behind fiber.
More specifically, he talked about how speed is not an important factor when
describing fiber. This was something that was counter intuitive. I was able to convey
this in my article and I really think this is something new that I can teach others.
Intiallly, it was this article that drew my attention to fiber optics.
[4] Honeywell Inc., "Outsmarting EMI," Mechanical Engineering, vol. 116, no. 9, p. 34, 1994.

This article described how fiber's physical properties insulate it from EMI. This
article was very helpful because I was describing the advantages of fiber, as
compared to copper. Even though this article was published by a corportation that
offers fiber optic solutions, it was a reliable source nevertheless. As far as I could
tell, it did not appear to be biased.
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[5] H. Guo, "Spectrum of Magnetic Core Inductor and Test Methods," Micromotors, vol. 43,
no. 10, pp. 105-109, 2010.

This article described how EMI from power sources can effect electronics within a
certain area. I was able to translate some of the ideas in this article into my
explanation of power lines. Even though this article was not as insightful as most my
other sources, I believe that it was important nevertheless. This article allowed me to
convey my idea through an example.
[6] Fiber Optics LAN Section of the Telecommunications Industry Association, "The Truth
About Fiber in Local Area Networks," 2002.

This paper was from a conference that addressed the growing importance of fiber
optics on the telecommunications industry. Most importantly, this paper discussed
how fiber has become cheaper over the decade. They argue that in some cases fiber
is essentially on par with copper in terms of cost. Even though this was a useful
source, there may have been some bias in this paper. This paper was published by a
group that actively promotes the use of fiber optics.
[7] B. Lavallee, "A Coherent Plan for Capacity Upgrades," Submarines Telecom Forums, pp.
13-14, January 2012.

This magazine mentioned the importance of submarine cables to international
telecommunications. This was another great source because it exposed me to
something that I did not know. Submarine cables handle nearly 100% of all internet
internet traffic. This was an amazing source and allowed me to talk about a real life
application of fiber.
[8] T. Carpenter, M. Eiger, D. Shallcross and P. Seymour, "Node placement and sizing for
copper broadband access networks," Annals of Operations Research, vol. 106, no. 1, pp.
199-228, 2001.

This article described the different configurations for fiber implementation. It briefly
talked about each configuration and the siutations in which they are the most
advantageous. With the help of this article, I was able to talk about how FTTN and
FTTH differ.
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