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Oct 26, 2013 (3 years and 5 months ago)

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EIE 650 Optical Communication

Lecture 1

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 1
st

clad
-
fibers by covering a bare fiber with a transparent of lower
refractive index.


Historical Development of Optical
Communications


1960


Maimen

demonstrated the 1
st

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.


Historical Development of Optical
Communications


1980’s


A 2
nd

generation of optical communication at
1300 nm with 0.5 dB/km for fiber attenuation.



1990’s


A 3
rd

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


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


The transmission
passbands

for installed fibers today are
0.85, 1.3, and 1.55
μ
m (near
-
infrared).



Wavelength of 1.6+
μ
m can be seen in some applications.



There are more than 25,000 GHz of capacity in each of
the three wavelength bands.


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





f
s

= 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.



Sol
n





Preview on Fiber Optic Communication


A
transmission
standard
developed
for optical communication
is
called SONET (
S
ynchronous
O
ptical
NET
work).



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

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


Optical fiber installations:


on poles


in ducts


undersea


Fiber Attenuation History

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

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
μ
m
wavelength.



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


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

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?


Sol
n

Example 3


By using the same cable as previous example, how many
TV channels could be sent via a cable.


Sol
n



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.


Generations of Fiber Usage



First generation: no fiber (copper link)



2
nd

generation:


Fiber used for point
-
to
-
point link only.


Multiplexing & switching carried out electronically.



3
rd

generation:


Fiber used for multiplexing and switching as well as point
-
to
-
point transmission.

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.


Fiber Bandwidth


We all know that






where
λ

= free
-
space wavelength


ν

= optical frequency



c = speed of light at free
-
space


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.


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.



Fiber Bandwidth

λ

(nm)

ν

(x10
14
Hz)

Δ
ν

(x10
13
Hz)

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


Space Division Multiplexing


Frequency Division Multiplexing


Time Division Multiplexing


Wavelength Division Multiplexing

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 =
L
ocal
A
rea
N
etwork (< 2 km)


MAN =
M
etropolitan
A
rea
N
etwork ( < 100 km)


WAN =
W
ide
A
rea
N
etwork (unlimited)