Download 1 Fiber Optics A survey of current and emerging technologies CPET

1
Fiber Optics
A survey of current and emerging technologies
CPET 384
Brian Bartholme & Scott Spaulding
Professor Steffen
December 4, 2006
2
Abstract
A survey of current and emerging trends related to fiber optic data communication. This
includes a history of fiber optics, a brief discussion of the current implementations of fiber, and a
more detailed analysis of the emerging fiber-to-the-premises trend, namely the system being
developed by Verizon Communications in the United States.
3
Fiber Optics: A survey of current and emerging technologies
In data communications, the primary objective is always to send data faster and more
efficiently, while reducing errors and overhead as much as possible. This desire, and
increasingly, the need for higher speeds of transmission have resulted in deference to the
ultimate benchmark of speed: light. Fiber optic technology, exploiting the properties of light, is
able to transmit data farther and faster than electrical transmission. The current prevailing
conditions of increased fiber demand and practicality are driving fiber's deployment and reach.
The purpose of this paper is to delve into the topic of fiber optic technology, investigating the
history of fiber, the basic concepts, its current usage, and the future of fiber in data
communications, namely in the form of fiber-to-the premises.
History of Fiber
The first communication device that used light waves was developed and patented by
Alexander Graham Bell in 1880. Named the Photophone, the device used sunlight to carry
voice waves from a transmitting mirror to a receiving station. A microphone was connected to
the transmitting mirror which had sunlight shown onto it. As a person spoke into the
microphone, the sound waves vibrated the mirror which in turn vibrated the sunlight. The
vibrating sunlight was reflected to a receiving station. The receiving station used a newly
discovered element called selenium whose electrical resistance changed with light. The
modulating sunlight beam turned the electrical resistance into electricity which drove a small
speaker, thus enabling a person on the receiving end to be able to hear the person speaking at
the transmitting end.
4
While this system worked, it was not at all practical. What was needed was a way to
channel the light through a medium just as electricity is channeled through wires. This idea
was demonstrated by focusing a light beam into a jet of water. The light would follow the
water as it curved downward. This phenomenon is known as Total Internal Reflection. The
light follows the flow of water because of the different densities of the water and the
surrounding air. Light travels more slowly in water than in air, so as the light reaches the
water/air boundary, it bends as it speeds up in the air. When the light traveling in the water
reaches a certain angle, it is reflected back into the water. At this point the water becomes a
light wave carrier. This principal was known and demonstrated in Bell’s era, but it was used
mostly as a science trick to amuse audiences. It wasn’t until almost 80 years later that this
principal was applied in the creation of fiber optic cable.
One thing that was needed to create fiber optic communications was a usable light source.
Ordinary light is a mixture of many frequencies that dissipate in all directions, so it was never
useful as a dependable light source for communication. The development of the laser in 1958
changed everything. A laser is a narrow order beam vibrating at a single pure frequency.
Lasers vibrate at around a thousand trillion times per second, so they are able to carry trillions
of bits of data on a single light wave.
With the development of the Laser a usable light source was now available. However, a
suitable medium was still needed to carry the light. Air was not practical as it would diffuse or
dissipate the light. Something pure and stable was needed. The answer came from the science
trick of the 1880’s: Total Internal Reflection. Instead of water, however, glass was used as the
medium. This development came about in 1956 through the efforts of University of Michigan
freshman Lawrence Curtis.
5
Until that time, doctors were using gastroscopes to look into the stomachs of patients.
These hollow tubes with mirrors on them were painful to the patients and difficult for the
doctors to use. For his freshman physics project, Curtis decided to try to develop a more
humane gastroscope using glass fibers. Through experimentation he found that glass fibers
would transmit an image over a few feet. However, when he bundled the fibers together the
light was refracted out of them rather than remaining within the fibers. This problem was
again related to Total Internal Reflection. When the fibers were separate there was a different
density boundary because of the air space between the fibers. With the fibers pressed together
there was no air, so there was no boundary difference. With the boundaries all the same, the
light could not reflect. Instead, it refracted out and traveled from one fiber to the next. Curtis
then came up with the idea of surrounding the fiber with a layer of purer glass, called a
cladding. Like the air, the cladding would provide a lower density barrier which would allow
the light wave to reflect back into the fiber. It would also protect the inner fiber, the core, and
allow multiple fibers to be bundled together. This core/cladding fiber would preserve the Total
Internal Reflection principal. Curtis was able to create such a fiber by inserting a glass rod into
a hollow glass tube of different density and melting the two together. He was able to pull the
glass into fibers of 40 feet or more, which far exceeded the 2 foot fibers he had originally
created. By bundling the fibers together he was able to create a working endoscope which was
tested on a patient two weeks later. Within a decade, fiber optic endoscopes were a routine
part of medicine.
The development of a fiber based endoscope was another giant step forward for fiber optics.
However, the problem of sending information over a large distance still remained. A fiber was
needed that could carry light waves farther than one kilometer, the distance that radio waves
6
could travel down coaxial wire. The fiber used for the endoscopes was not good enough for this
purpose, which prompted a search for a purer substance. The resolution to this problem came in
1970 from three men who worked for Corning Glass in upstate New York. Peter Schultz, Robert
Maurer, and Don Keck developed the technique of creating a fiber of fused silica: the purest
known form of glass. Fused silica is a very high temperature glass that is very difficult to melt
and draw. The trio was able to create a hollow cylinder of pure silica, the inside of which they
coated with a slightly less pure layer of silica. The coating was done initially by pulling the
smoke like substance through the cylinder with a vacuum cleaner. The cylinder was then heated
whereupon it collapsed on itself; the outside cylinder forming the cladding and the inside layer
forming the core. The melted glass was then drawn to form the actual fiber strand. Using laser
technology and the newly engineered form of fiber, the age of fiber optic cabling was born. By
the year 2000, an estimated 260 million kilometers of fiber optic cable had been installed,
enough to go to the moon and back 350 times.
Current Technologies
Present day usage of fiber is mostly attributable to mega-bandwidth carrying network
backbones, public utility companies, and government agencies. These entities have been using
fiber optics for several decades. Fiber is an excellent fit for these purposes, providing massive
amounts of bandwidth over long distances. The benefits of fiber, until just recently,
were mostly enjoyed only by those entities that could afford it or those that absolutely needed
the technology. However, decreasing prices and increases in demand are changing the
current landscape so as to extend fiber coverage to the general public: more specifically, right
to a customer's premises. This provides consumers and businesses with the same benefits
7
already enjoyed by large scale businesses. The entire concept of fiber to the premises is
redefining fiber's scope and examining the Fiber To The Premises (FTTP) process is a
worthwhile endeavor for understanding future developments.
Procession of data from satellite to the home
Satellite and super-head end
Looking at the FTTP panorama, the Super Head-End (SHE) is equivalent to the mouth of a
large funnel, gathering massive amounts of data and channeling it down towards the end that is
the customer's premises. The process begins with a farm of satellites, taking in feeds from
essentially anywhere on the globe. The satellite signals are then processed by integrated
receiver/decoders (IRDs.) These devices take in the pure satellite signal, decode its signaling
scheme, extract the digital information contained within, and pass that data onto a digital
multiplexer. The multiplexer then combines the many signals and sends them out as one single
signal, and at a higher data rate.
8
Figure 1 - Conceptual breakdown of SHE and VHO components
In the FTTP scenario, the multiplexer takes the television signals from the IRDs and
melds them together as one MPEG-2 video signal. This signal, which is still digital and not yet
optical, is sent to a Smart-stream Encryptor Modulator (SEM) using the Asynchronous Serial
Interface protocol. The SEM takes the multiplexer output and processes it to create an optical,
Gigabit-bandwidth signal. The signal is also modulated using a 64/256QAM
(quadrature amplitude modulation) scheme, and is then encrypted. After the digital signal
processing has been completed, the data is sent downstream to the final component of the super
head-end’s operational scope, the SONET multiplexer.
Thus far, the video content has been pulled off of the satellites, converted into an optical
signal, modulated, and encrypted. The responsibility now lies with the SONET multiplexer to
make sure that this polished signal is distributed beyond the super head-end. Distributing the
signal necessitates being part of a network. As evidenced by its name, the SONET multiplexer
is a node on a SONET OC-192 wide area network transmitting at 10 Gigabits per second. This
9
high-speed, high-bandwidth, high distance-covering SONET network contains two Super
Head-Ends and multiple Video Hub Offices linked together by two separate networks, which
provide redundancy. The SONET network acts as a portal from which the Video Hub Offices,
the next major component of the FTTP scheme, can obtain national content signals for
incorporation into the final product that is distributed to the customer’s premises.
Video Hub Office (VHO)
The Video Hub Offices (VHOs) are the mix masters of the process. They take in content
from a number of sources and multiplex them together to create one signal that is a combination
of services and content. The VHOs are attached to the SONET network, which enables them to
capture the national feeds being circulated on the ring from the SHE. VHOs also handle
localized content that includes broadcasts that are specific to the geographic area surrounding the
VHO. These signals would include local television channels and PEG channels (Public,
Education, Government). In addition they have the capability to distribute the Emergency Alert
System service (EAS) and Video on Demand (VOD), and can also facilitate ad insertion, which
incorporates commercials as part of the video broadcasts.
10
Figure 2 - Conceptual breakdown of VHO components
The first task of the VHO is to extract the signal from the SONET network and de-multiplex
it. Next, the signal is sent through a Smart-stream Encryptor Modulator for decryption. The
output uses the Asynchronous Serial Interface protocol for transmission. At this point, the local
content, PEG content, and advertisements are added to the signal and it is once again sent
through a Smart-stream Encyptor Modulator, this time for encryption. This signal, along with
the VOD and EAS signals are then routed to the Video Serving Office (VSO).
As mentioned, the EAS signal is received at the VHO and routed to the VSO, but first it is
decoded and then demodulated into an analog and a digital signal. This is to ensure that both
analog and digital types of receivers will pick up the emergency signal. The digital signal is
primarily used with digital televisions and set-top boxes. The analog signals are used by
standard televisions. As the signal enters a home, if a set-top box is used, the digital signal will
11
simply change the channel of the set-top box to that of the EAS system. If a box is not used, a
RF generator will cause the current channel to be preempted with the EAS signal. The VHO
portion of the FTTP process is concluded once the appropriate content is routed to the VSO,
bringing the video portion of FTTP one step closer to the end user.
Video Serving Office (VSO)
The Video Serving Office (VSO) is the next step in the process of the signal generation. For
a given city or geographic area there will only be one VHO; however, there will be several
VSOs. The VSOs are usually placed where current telephone company Central Offices (COs)
are located. This is because COs are the origin of the phone and data (Internet) signals for a
customer. Since a CO services only a specific area of a city or region, there needs to be a VSO
for every CO so that all the customers in a fiber region will be able to receive service. This also
makes it easier to tie the signals together, and reduces facility and maintenance costs.
The data signal is fed into a router, such as the Juniper ERX-1440, and is then sent to the
Optical Line Terminal (OLT). The Juniper ERX-1440 Broadband Services Router is a high
performance 40Gbps routing platform designed to support large central office deployments. Its
JUNOSe Operating System can handle the bandwidth demands of multiplay services and can
support a full suite of Internet routing protocols, including BGP-4, IS-IS, OSPF, and RIP. It is
capable of offering security services for Internet Protocol television (IPTV), and also supports
Gigabit Ethernet speeds.
Along with the data stream, the telephone signal is also brought into the OLT which
combines the signals and converts them to an optical wave form. The Motorola AXS2200 is an
12
example of a leading edge OLT being used today. The light wave is then sent to a wave division
multiplexer (WDM). The video signal from the VHO, already a light wave, is also sent to the
WDM, but only after being run through an erbium doped fiber amplifier (EDFA) to strengthen
the signal. From here the signal leaves the VSO and heads toward the customer’s premises.
Figure 3 - Conceptual breakdown of VSO and customer premises components
Customer’s Premises
Before a fiber reaches the customer's premises it is first routed to a distribution hub. These
hubs are placed throughout the VHO's territory and their task is to split the fiber into multiple
output fibers, which provides distribution to multiple customers from one single input fiber.
Physically, a hub is an outdoor distribution enclosure, like the OmniReach Fiber
Distribution Hubs produced by ADC. These are located in the local neighborhoods or
geographic areas of the intended customer’s premises (see Figure 1.) The OmniReach hubs use
13
centralized splitting, as opposed to cascading splitting, because of the advantages centralized
splitting provides. These advantages include higher efficiency rates for the OLN cards, easier
testing and troubleshooting, minimization of signal loss, and a reduction of the overall number of
network components. Splitting within the hubs is carried out by Passive Optical Network splitter
modules taking a 1x32 approach. This means that one module will split a single signal into thirty
two individual fibers (see Figure 2.) These 32 fibers are routed to distribution terminals that are
placed within a few hundred feet of a customer’s premises. When a customer requests fiber
optic service, a “drop”, either aerial or buried, will connect the distribution terminal to the
Optical Network Terminal (ONT) that is placed on the customer’s residence. Hence the
acronym FTTP (Fiber To The Premises.)
Fiber cables are laid from the VSO to the hub using either aerial or buried pathways. The
individual fibers are fused or spliced together to create a network of continuous glass from one
point to the other. At the VSO and the hub, the fibers are terminated using an Angled Polished
Connector (APC.) These connectors are a snap-in type of connector that provides for easy
connection and re-connection to other fibers (see Figure 3.) The APC snaps into a small coupler
that allows another APC to be snapped in on the other side. The end of the fiber in the APC is
polished and angled so that when two APCs are coupled together, the angles line up and mate in
order to form a continuous fiber strand (See Figure 4.) The angle of the connection helps to
eliminate reflection of the signal and “ghosting;” which is a projection of a faint signal past the
actual ending point of the fiber. This is similar to looking into a mirror and seeing several, faint
“ghost” images behind the original image.
Like copper lines, there is a certain amount of loss of signal associated with fiber
connections and the distances of the networks. For each connector there is an average loss of 0.3
14
dB. Using singlemode fiber you can expect losses of about 0.5 dB per km for 1330 nm, to 0.4
dB per km for 1550 nm. Splice losses can range from almost nothing to several dB, but
generally, any loss over 0.3 db is unacceptable (see Figure 5.) The splitters used in the hubs
incur a loss of about 14 db. Video services are transmitted on the 1550 nm signal and this
wavelength is most susceptible to loss. Therefore, for a network that will be providing video
service, a total db loss from the VSO to the customer premises should not exceed about 20 db.
The customer premises are like the end of the funnel of fiber optic information. The video,
data, and voice signals that have been channeled down the network are now separated into their
constituent electrical signals. This process begins with the signal from the hub's splitter being
sent on an individual fiber to an Optical Network Terminal (ONT) that is located on the outside
of a customer’s building. The ONT acts as a demodulator that separates the three signals.
15
Figure 4 - Actual ONT model in usage
One ONT that is currently being used is the ONT1000V Optical Network Terminal
produced by Motorola. The major functions of the ONT1000V include Triplexer, PON MAC,
and telephony. The ONT is able to access the three wavelengths of the PON (1310 nm, 1490
nm, and 1550 nm) by utilizing the Triplexer. This contains an analog detector, data detector,
upstream laser, and wave division multiplexer. Data on the PON is handled by the PON MAC
within the ONT, which filters traffic intended for the ONT and disregards data intended for other
devices. The PON MAC also takes care of upstream data, making sure that it is formatted
correctly and synchronized. Analog voice traffic, also known as Plain Old Telephone Service
16
(POTS), is handled by the telephony functionality. Analog voice waveforms are converted into
digital data packets, enabling the ONT to provide telephone service over fiber. A digital signal
processor makes the conversions between analog and digital voice streams possible, while also
having the capability to detect dial tones and busy signals. The ONT100V is capable of handling
four separate telephone lines. Besides telephone jacks, the ONT also has a connection for a RJ45 Ethernet connection, for computer networking and Internet usage, and also a cable-out jack,
for connecting cable television to the customer's premises.
Conclusion
The future of fiber is very promising and exciting. The developments and discoveries that
led to the harnessing of the power of light are as amazing as the technology itself. The
commercial use of fiber and its acceptance in high requirement situations have paved the way for
the next phase in the history of fiber, the FTTP movement. This deployment is redefining who
gets to use fiber and for what purposes. FTTP is intriguing to study, and the ways in which all of
the components come together is an engineering marvel. It certainly seems that the future will
be 'brighter' because of the rising popularity of fiber.
17
References
ADC Telecommunications, Inc. (2005). OmniReach™ FTTX Solutions: Fiber Distribution
Terminals. Minneapolis, MN: Author.
ADC Telecommunications, Inc. (2006). OmniReach™ FTTX Solutions: Passive Optical Splitter
Modules. Minneapolis, MN: Author.
Bartholme, Brian. (2006, October 30). [Interview with John Ruzzo, Verizon Construction
supervisor].
Bartholme, Brian. (2006, November 3). [Interview with Dave Smith, Verizon Customer Zone
Technician].
DeCusatis, Casimer. (2006). Fiber optic essentials. Amsterdam ; Boston : Elsevier/Academic
Press
Hayes, Jim. (2006). Fiber optics technician's manual. Clifton Park, NY : Thomson Delmar
Learning
Juniper Networks Inc. (2004). E-series Broadband Services Routers. Sunnyvale, CA: Author.
Juniper Networks Inc. (2004). JUNOSe Datasheet. Sunnyvale, CA: Author.
Meardon, S. L. (1993). Wymer. The elements of fiber optics. Englewood Cliffs, N.J.:
Regents/Prentice Hall
Motorola, Inc. (2006). Installation Guide ONT1000V Optical Network Terminal. Horsham, PA:
Author.
Motorola, Inc. (n.d.). Motorola AXS2200 Optical Line Terminal. Retrieved November 3, 2006
from http://www.motorola.com/content.jsp?globalObjectId=5556-8675-8680
18
Motorola, Inc. (2003). SEM Application Note. Horsham, PA: Author.
Palfreman, Jon. (Writer, Producer, Director). (2004, April 27). Light Speed. Fort Wayne: PBS
Reed, Keith. (2006, November 2). An urban fiber-optic challenge. The Boston Globe.
Verizon. (2005) FiOS TV: Verizon FiOS TV / Video Overview. Retrieved November 22, 2006,
from http://netlearn.verizon.com/NL_V6/ProtectedContent/Catalog/CatalogUI.aspx
Wikipedia. (Oct. 2006). Fiber-optic communication. Retrieved November 2, 2006 from
http://en.wikipedia.org/wiki/Fiber-optic_communication
Wikipedia. (Oct. 2006). Optical fiber. Retrieved November 2, 2006 from
http://en.wikipedia.org/wiki/Fiber_optics
Wikipedia. (Oct. 2006). Passive Optical Network. Retrieved November 2, 2006 from
http://en.wikipedia.org/wiki/Passive_optical_network
19
Figure Caption
Figure 1. Hub
Figure 2. Four Splitters
20
Figure 3. Angled Polished Connector
Figure 4. Two APCs snapped in a coupler
Figure 5. Four fiber splices in a splice tray