ENE623/EIE 696 Optical Networks
Lecture 1
Historical Development of Optical
Communications
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1790 – Claude Chappe invented ‘optical telegraph’.
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1880 – Graham Bell invented ‘photophone’.
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1930 – Heinrich Lamm presented unclad-fibers, but it
showed poor performance.
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1954 – van Heel and Kapany reported about the 1st cladfibers by covering a bare fiber with a transparent of lower
refractive index.
Historical Development of Optical
Communications
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1960 – Maimen demonstrated the 1st laser for
communications.

1966 – Kuo and Hockham introduced fiber
communications with low attenuation (< 20 dB/km).
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1970 – Maurer, Keck, and Schultz made a single-mode
fused silica fiber (very pure with high melting point and a
low refractive index) for 633 nm wavelength of HeNe
laser.

1977 – Fibers used at 850 nm from GaAlAs laser.
Historical Development of Optical
Communications

1980’s – A 2nd generation of optical communication at
1300 nm with 0.5 dB/km for fiber attenuation.

1990’s – A 3rd generation operates at 1550 nm with fiber
loss of 0.2 dB/km with EDFA serving as an optical
amplifier . Signals also could be sent via WDM.
Preview on Fiber Optic Communication

Basic schematic diagram
Preview on Fiber Optic Communication

The advantages of optical fiber communication over
electrical based system are
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Low attenuation
High bandwidth
Immune to electro-magnetic interference
Short circuiting, Earthing, and Fire Free
Low in weight and volume
Data security
Preview on Fiber Optic Communication
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The transmission passbands for installed fibers today are
0.85, 1.3, and 1.55 μm (near-infrared).

Wavelength of 1.6+ μm can be seen in some applications.
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There are more than 25,000 GHz of capacity in each of
the three wavelength bands.
Preview on Fiber Optic Communication
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Digital transmission – The sampling theorem says that
an analog signal can be accurately transmitted if
sampling rate is twice the highest frequency
contained in that signal.

Let R be the required transmission rate. R can be expressed
by
R  m. f s
where m = number of bits/sample
fs = sampling frequency = 2(f)
Preview on Fiber Optic Communication
Message Type
Used bandwidth(B)
Voice (telephone)
4 kHz
Music -- AM
10 kHz
Music -- FM
200 kHz
TV (Video + Audio)
6 MHz
Preview on Fiber Optic Communication
Number of Voice channels
Transmission
Designation
Signaling Designation
Data Rate
1
-
-
64 kb/s
24
T1
DS-1
1.544 Mb/s
48 (2-T1 systems)
T1C
DS-1C
3.152 Mb/s
96 (4-T1 systems)
T2
DS-2
6.312 Mb/s
672 (7-T2 systems)
T3
DS-3
44.735 Mb/s
1344 (2-T3 systems)
T3C
DS-3C
91.053 Mb/s
4032 (6-T3 systems)
T4
DS-4
274.175 Mb/s
Example 1

A telephone system has m = 8 bits/sample. Find R.

Soln
Preview on Fiber Optic Communication
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A transmission standard developed for optical communication
is called SONET (Synchronous Optical NETwork).
Transmission
Designation
(electrical)
(optical)
STS-1
SDH system
Data Rate(Mb/s)
OC-1
-
51.84
STS-3c
OC-3
STM-1
155.52
STS-12
OC-12
STM-4
622.08
STS-24
OC-24
STM-8
1,244.16
STS-48
OC-48
STM-16
2,488.32
STS-96
OC-96
STM-32
4,976.64
STS-192
OC-192
STM-64
9,953.28
STS-768
OC - 768
STM-128
39,813.12
Preview on Fiber Optic Communication
Band
Descriptor
Range(nm)
O-band
Original
1260 - 1360
E-band
Extended
1360 -1460
S-band
Short wavelength
1460 - 1530
C-band
Conventional
1530 – 1565
L-band
Long wavelength
1565 - 1625
U-band
Ultra-long wavelength
1625 - 1675
Installations
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Optical fiber installations:
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on poles
in ducts
undersea
Fiber Attenuation History
Preview on Fiber Optic Networks
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Fiber-To-The-Home (FTTH)
2.5 Gbps  Mid 90’s
10 Gbps  y2k
40 Gbps and beyond  state of art
Preview on Fiber Optic Networks
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Now a number of channels per fiber is more than 128.
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This was increased from 32 channels/fiber in 2004.
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The link attenuation is less than 0.2 dB/km at 1.55 μm
wavelength.
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BER can be achieved at 10-15 with a help of Er-doped fiber
amplifier (EDFA).
Optical Fiber
Source: ARC Electronics
http://www.arcelect.com/fibercable.htm
Fibers
Source: Optical Fiber Communications, G.Keiser, McGraw Hill.
Connectors
Source: ARC Electronics
http://www.arcelect.com/fibercable.htm
Optical communication systems
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Multiplexing refers to transmission of multiple channels
over one fiber.
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Channels can be data, voice, video, and so on.
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We may classify the communication systems into 3
classes as:
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Point-to-point link
Multipoint link
Network
Example 2
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A cable consists of 100 fibers. Each fiber can carry signals
of 5 Gbps. If audio message encoded with 8 bits/sample is
being sent, how many conversations can be sent via one
cable?
Soln
Example 3
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By using the same cable as previous example, how many
TV channels could be sent via a cable.
Soln
Generations of Fiber Usage
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Bandwidth and error rate improved (fatter links), but
propagation delay not changed (same length).
Source: Fiber Optic Network Paul E. Green, Prentice Hall.
Generations of Fiber Usage
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First generation: no fiber (copper link)
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2nd generation:
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Fiber used for point-to-point link only.
Multiplexing & switching carried out electronically.
3rd generation:
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Fiber used for multiplexing and switching as well as point-topoint transmission.
Generations of Fiber Usage
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Copper links
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Copper links are more vulnerable to outside influence since
moving electrons influence each other.
It is also affected by electromagnetic wave (EM wave).
Fiber links
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Moving photons of light in a fiber do not interact with other
moving photons.
EM wave has no effect on a fiber as well.
Fiber Bandwidth
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We all know that
  c

where λ = free-space wavelength
ν = optical frequency
c = speed of light at free-space
Fiber Bandwidth
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At  = 1.5 µm, the attenuation is about 0.2 dB/km, and
there is a window about  = 200 nm wide between
wavelengths having double that number of dB per
kilometer.
 

c 
2
The useful bandwidth is about 25,000 GHz.
Fiber Bandwidth
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This can applied to  = 1.3 µm and 0.85 µm as well.
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For 0.85 µm, this band is not defined by an attenuation
standpoint, but by the range which GaAs components can
be easily made.
Fiber Bandwidth
λ (nm)
ν (x1014Hz)
Δν (x1013Hz)
Δν/ν
0.85
3.53
2.5
0.07
1.3
2.31
2.5
0.11
1.55
1.93
2.5
0.13
Multiplexing
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Space Division Multiplexing
Frequency Division Multiplexing
Time Division Multiplexing
Wavelength Division Multiplexing
Wavelength-Division Multiplexing
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For example, 16 channel WDM using 1,300 nm or 1,550
nm with 100 GHz channel spacing.
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Therefore, bandwidth = 16 x 100 = 1,600 GHz.
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LAN = Local Area Network (< 2 km)
MAN = Metropolitan Area Network ( < 100 km)
WAN = Wide Area Network (unlimited)
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