Download - ENE623/EIE 696 Optical Networks
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ENE623/EIE 696 Optical Networks
Lecture 1
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Historical Development of Optical Communications 1790 – Claude Chappe invented ‘optical
telegraph’.
1880 – Graham Bell invented ‘photophone’.
1930 – Heinrich Lamm presented unclad-fibers, but it showed poor performance.
1954 – van Heel and Kapany reported about the 1st clad-fibers by covering a bare fiber with a transparent of lower refractive index.
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Historical Development of Optical Communications 1960 – Maimen demonstrated the 1st laser for
communications.
1966 – Kuo and Hockham introduced fiber communications with low attenuation (< 20 dB/km).
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.
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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.
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Preview on Fiber Optic Communication Basic schematic diagram
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Preview on Fiber Optic Communication The advantages of optical fiber
communication over electrical based system are Low attenuation High bandwidth Immune to electro-magnetic interference Short circuiting, Earthing, and Fire Free Low in weight and volume Data security
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Preview on Fiber Optic Communication 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.
There are more than 25,000 GHz of capacity in each of the three wavelength bands.
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Preview on Fiber Optic Communication 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
where m = number of bits/sample
fs = sampling frequency = 2(f)
. sR m f
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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
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Preview on Fiber Optic CommunicationNumber of Voice
channelsTransmission
DesignationSignaling 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
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Example 1 A telephone system has m = 8 bits/sample.
Find R.
Soln
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Preview on Fiber Optic Communication A transmission standard developed for optical
communication is called SONET (Synchronous Optical NETwork).
Transmission
(electrical)
Designation
(optical)SDH system Data Rate(Mb/s)
STS-1 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
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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
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Installations
Optical fiber installations: on poles in ducts undersea
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Fiber Attenuation History
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Preview on Fiber Optic Networks Fiber-To-The-Home (FTTH)
2.5 Gbps Mid 90’s
10 Gbps y2k
40 Gbps and beyond state of art
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Preview on Fiber Optic Networks Now a number of channels per fiber is more
than 128.
This was increased from 32 channels/fiber in 2004.
The link attenuation is less than 0.2 dB/km at 1.55 μm wavelength.
BER can be achieved at 10-15 with a help of Er-doped fiber amplifier (EDFA).
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Optical Fiber
Source: ARC Electronics http://www.arcelect.com/fibercable.htm
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Fibers
Source: Optical Fiber Communications, G.Keiser, McGraw Hill.
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Connectors
Source: ARC Electronics http://www.arcelect.com/fibercable.htm
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Optical communication systems Multiplexing refers to transmission of multiple
channels over one fiber.
Channels can be data, voice, video, and so on.
We may classify the communication systems into 3 classes as: Point-to-point link Multipoint link Network
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Example 2 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
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Example 3 By using the same cable as previous example,
how many TV channels could be sent via a cable.
Soln
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Generations of Fiber Usage Bandwidth and error rate improved (fatter
links), but propagation delay not changed (same length).
Source: Fiber Optic Network Paul E. Green, Prentice Hall.
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Generations of Fiber Usage
First generation: no fiber (copper link)
2nd generation: Fiber used for point-to-point link only. Multiplexing & switching carried out electronically.
3rd generation: Fiber used for multiplexing and switching as well
as point-to-point transmission.
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Generations of Fiber Usage Copper links
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 Moving photons of light in a fiber do not interact
with other moving photons. EM wave has no effect on a fiber as well.
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Fiber Bandwidth We all know that
where λ = free-space wavelength ν = optical frequency
c = speed of light at free-space
c
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Fiber Bandwidth 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.
The useful bandwidth is about 25,000 GHz.
2
c
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Fiber Bandwidth This can applied to = 1.3 µm and 0.85 µm as
well.
For 0.85 µm, this band is not defined by an attenuation standpoint, but by the range which GaAs components can be easily made.
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Fiber Bandwidth
λ (nm) ν (x1014Hz) Δν (x1013Hz)
Δν/ν
0.85 3.53 2.5 0.071.3 2.31 2.5 0.111.55 1.93 2.5 0.13
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Multiplexing Space Division Multiplexing Frequency Division Multiplexing Time Division Multiplexing Wavelength Division Multiplexing
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Wavelength-Division Multiplexing For example, 16 channel WDM using 1,300 nm
or 1,550 nm with 100 GHz channel spacing.
Therefore, bandwidth = 16 x 100 = 1,600 GHz.
LAN = Local Area Network (< 2 km) MAN = Metropolitan Area Network ( < 100
km) WAN = Wide Area Network (unlimited)