Transcript No Slide Title

Optical Technologies and Lightwave Networks
Outline:
 Optical Technologies
 Optical Fibers, Fiber Loss and Dispersion
 Lightwave Systems and Networks
 Multiplexing Schemes
 Undersea Fiber Systems
 Lightwave Broadband Access
 Optical Networks
1
Need for Optical Technologies
• huge demand on bandwidth nowadays
 need high capacity transmission
• electronic bottleneck:
• speed limit of electronic processing
• limited bandwidth of copper/coaxial cables
• optical fiber has very high-bandwidth (~30 THz)
 suitable for high capacity transmission
• optical fiber has very low loss (~0.25dB/km @1550
nm)
 suitable for long-distance transmission
2
Light Wave
amplitude
position/distance
wavelength
• electromagnetic wave
• carry energy from one point to another
• travel in straight line
• described in wavelength (usually in mm or nm)
• speed of light in vacuum = 3108 m/s
3
Reflection and Refraction of Light
Reflection
Refraction
>
Incident
light
Reflected
light
 
Reflecting
surface
Incident angle = reflected angle 
 > c

Medium 1
Medium 2

 
• medium 1 is less dense (lower refractive
index) than medium 2
• light path is reversible
• If incident light travels from a denser
medium into a less dense medium and
the incident angle is greater than a certain
value (critical angle c)  Total Internal
Reflection
4
Optical Fiber
cladding
light beam
core
•
made of different layers of glass, in cylindrical form
•
core has higher refractive index (denser medium) than the cladding
•
light beam travels in the core by means of total internal refraction
•
the whole fiber will be further wrapped by some plastic materials for
protection
•
in 1966, Charles K. Kao and George A. Hockham suggested the use of
optical fiber as a transmission media for information
5
Optical Fiber (cont’d)
• Fiber mode describes the path or direction of the light beam
travelling in the fiber
• number of fiber modes allowed depends on the core diameter and
the difference of the refractive indices in core and cladding
Single-mode Fiber
Multi-mode Fiber
• smaller core diameter
• larger core diameter
• allow only one fiber mode
• allow more than one fiber modes
• typical value: 9/125mm
• typical value: 62.5/125mm
6
Optical Fiber (cont’d)
Advantages of optical fiber:
• large bandwidth  support high capacity transmission
• low attenuation  support long-distance transmission
• small and light in size  less space
• low cost
• immune to electromagnetic interference
7
Fiber Attenuation
• optical power of a signal is reduced after passing through a piece of fiber
• wavelength-dependent
low loss wavelength ranges: 1.3mm (0.4-0.6 dB/km), 1.55mm (0.2-0.4 dB/km)
 suitable for telecommunications
8
Fiber Dispersion
• Inter-modal dispersion (only in multi-mode fibers):
different fiber modes takes different paths
 arrived the fiber end at different time
 pulse broadening  intersymbol interference (ISI)  limit bit-rate
• Intra-modal dispersion (in both single-mode and multi-mode fiber):
different frequency components of a signal travel with different speed
in the fiber
 different frequency components arrived the fiber end at different
time
 pulse broadening  limit bit-rate
9
Fiber Dispersion
Dispersion (ps/(km•nm))
20
Standard
10
Typical values:
standard fiber:
Dispersionflattened
~ 0 ps/(km• nm) @1300 nm
~17 ps /(km• nm) @1550 nm
0
dispersion-shifted fiber:
~0.5 ps /(km• nm) @1550 nm
Dispersionshifted
-10
-20
1.1
1.2
1.3
1.4
1.5
1.6
1.7
Wavelength (mm)
10
System Capacity
 fiber attenuation  loss in optical power  limit transmission distance
 fiber dispersion  pulse broadening  limit transmission bit-rate
11
Laser Source and Photodetector
Laser source
• generate laser of a certain
wavelength
Input
electrical data
• made of semiconductors
output
optical
power
• output power depends on input
electric current
• need temperature control to
stabilize the output power and
output wavelength (both are
temperature dependent)
optical power
(photons)
wavelength
l
input
electric
threshold current current
Photodetector
• convert incoming photons into
electric current (photo-current)
optical power
(photons)
photo-current
12
Multiplexing Schemes
Multiplexing: transmits information for several connections simultaneously
on the same optical fiber
Time Division Multiplexing (TDM)
A2 A1
A
C2 B2 A2 C1 B1 A1
B2 B1
time
B
C2 C1
C
l
• only require one wavelength (one laser)
• if channel data rate is R bits/sec, for N channels, the system data rate is
(R  N) bits/sec
13
Multiplexing Schemes
Subcarrier Multiplexing (SCM)
fA
freq
A
fB
B
fA fB fC
freq
freq
fC
C
freq
l
• multiple frequency carriers (subcarriers) are combined together
• only require one wavelength (one laser) (optical carrier)
• suitable for video distribution on fiber
14
Multiplexing Schemes
Wavelength Division Multiplexing (WDM)
lA
lA lB lC
wavelength
A
lB
B
lC
C
wavelength
multiplexer
• one distinct wavelength (per laser) per sender
wavelength spacing:
0.8 nm (100-GHz)
• wavelength multiplexer/demultiplexer are needed to combine/separate wavelengths
• if channel data rate per wavelength is R bits/sec, for N wavelengths, the system data
rate is (R  N) bits/sec
• suitable for high capacity data transmission
15
Multiplexing Schemes
Hybrid Types (TDM/WDM, SCM/WDM)  higher capacity
TDM/WDM
TDM stream
SCM/WDM
lA lB lC
lA
wavelength
C
f2
f3
lB
f2
lB
B
f3
lC
lC
f1
wavelength
multiplexer
f2
f3
wavelength
A
f1
B
TDM stream
lA
f1
A
TDM stream
lA lB lC
C
wavelength
multiplexer
16
Transmission System Capacity
132 Ch
1 Ch TDM
17
Optical Amplifier
G
• no Electrical-to-Optical (E/O) or Optical-to-Electrical (O/E) conversion
• can amplify multiple wavelengths simultaneously
• Semiconductor Optical Amplifier
• Fiber-Amplifier
• Erbium-doped fiber amplifier (EDFA) : operates at 1550 nm
transmission window (1530-1560 nm) (mature and widely
deployed nowadays)
• Pr3+ or Nd3+ doped fiber amplifier: operates at 1310 nm
transmission window (not very mature)
• ultra-wideband EDFA: S-band (1450-1530 nm), C-band (1530-1570
nm), L-band (1570-1650 nm)
18
Lightwave Systems
Traditional Optical Fiber Transmission System
Low-Rate
Data Out
Low-Rate
Data In
E
M
U
X
E
REG
RPTR
XMTR
REG
RPTR
RCVR
Opto-Electronic Regenerative Repeater
DET
AMP
EQ
DEC
AMP
D
M
U
X
LASER
TMG
REC



•
Single-wavelength operation, electronic TDM of synchronous data
Opto-electronic regenerative repeaters, 30-50km repeater spacing
Distortion and noise do not accumulate
Capacity upgrade requires higher-speed operation
19
Lightwave Systems
Optical Fiber Transmission System
Data In
XMTR
l1
l2
XMTR
XMTR






lN
O
M
U
X
O
OA
OA
OA
l1
l2
Data Out
RCVR
D
RCVR
M
U
X lN RCVR
Multi-channel WDM operation
Transparent data-rate and modulation form
One optical amplifier (per fiber) supports many channels
80-140 km amplifier spacing
Distortion and noise accumulate
Graceful growth
20
Undersea Fiber Systems
Design Considerations
 span distance
 data rate
 repeater/amplifier spacing
 fault tolerance, system monitoring/supervision, restoration, repair
 reliability in components: aging (can survive for 25 years)
 cost
21
Undersea Fiber Systems
AT&T
22
Undersea Fiber Systems
SYSTEM
TIME
BANDWIDTH/
BIT-RATE
0.2 MHz
TAT-1/2
1955/59
HAW-1
1957
TAT-3/4
1963/65
HAW-2
1964
1.1 MHz
H-G-J
1964
TAT-5
1970
HAW-3
1974
6 MHz
H-G-O
1975
TAT-6/7
1976/83
30 MHz
TAT-8
1988
HAW-4
1989
280 Mb/s
TPC-3
1989
TAT-9
1991
TPC-4
1992
560 Mb/s
TAT-10/11
1992/93
TAT-12
1995
5 Gb/s
TPC-5
1995
TAT: Trans-Atlantic Telecommunications
TPC: Trans-Pacific Cable
NUMBER OF
BASIC CHANNELS
48
COMMENTS
140
COPPER COAX
ANALOG
VACUUM TUBES
840
Ge TRANSISTORS
4,200
Si TRANSISTORS
OPTICAL FIBER
DIGITAL
l = 1.3 mm
8,000
16,000
24,000
122,880
l = 1.55 mm
OPTICAL AMPLIFIERS
l = 1.55 mm
23
Undersea Fiber Systems
FLAG: Fiberoptic Link Around the Globe (10Gb/s SDH-based, 27,000km, service in 1997)
• Tyco (AT&T) Submarine Systems Inc., & KDD Submarine Cable Systems Inc.
• 2 fiber pairs, each transporting 32 STM-1s (5-Gb/s)
24
Undersea Fiber Systems
Africa ONE: Africa Optical Network
(Trunk: 40Gb/s, WDM-SDH-based, 40,000km trunk, service in 1999)
•
Tyco (AT&T) Submarine Systems Inc. &
Alcatel Submarine Networks
•
54 landing points
•
8 wavelengths, each carries 2.5Gb/s
•
2 fiber pairs
25
Lightwave Broadband Access
Passive Optical Network (PON) Remote
Node
passive optical
splitter
electrical
repeater
Headend
Fiber
Coaxial Cable
•
Remote Node performs optical-to-electrical conversion
•
Hybrid Fiber-Coax (HFC), Fiber-to-the-Curb (FTTC), Fiber-to-the-Home
(FTTH)
•
Distribution system: video, TV, multimedia, data, etc.
•
Two-way communications: upstream and downstream
•
Subcarrier multiplexing (single wavelength)
26
Lightwave Broadband Access
WDM-PON
l1
l1 , … , lN
Headend
multi-wavelength
wavelength
source
demultiplexer
Remote
Node
l2
lN-1
electrical
repeater
lN
• WDM-PON: Wavelength Division Multiplexed Passive Optical Network
• use multiple wavelengths, each serves a certain group of users
• higher capacity
27
Lightwave Networks
 Transmission
 Multi-access
 Channel add-drop
 Channel routing/
switching
28
Lightwave Networks
• connection between two hosts via a channel  need to access channel
• Channel: Wavelength (in WDM network), Time Slot (in TDM network)
• Tunable transmitter and tunable
receiver (TTTR)
A
• most flexible, expensive
• Fixed transmitter and tunable receiver
(FTTR)
T R
B
T R
• each node sends data on a fixed channel
• receiver is tuned to receiving channel before
data reception
• have receiver contention problem
• Tunable transmitter and fixed receiver
(TTFR)
C
D
T R
T R
• each node receives data on a fixed channel
• transmitter is tuned to the receiving channel
of the destination node before sending data
29
Lightwave Networks
l1, l2, l3
l1, l2*, l3
Add-drop Multiplexer
(ADM)
Channel add-drop
l2
DROP
l2*
ADD
l1
Wavelength ADM:
l1, ..., lN
l1*, ..., lN
lN
l1*
ADD
l1
DROP
30
Lightwave Networks
Static Optical Cross-Connect: Channel routing
(fixed wavelength routing pattern)
l11, l12, l13, …, l1M
l11, lN2, … , l3(N-1), l2N
l21, l22, l23, …, l2M
l21, l12, lN3, … , l3N
l31, l32, l33, …, l3M
l31, l22, l13, lN4, ...
lN1, lN2, lN3, …, lNM
lN1, … , l3(N-2), l2(N-1), l1N
31
Lightwave Networks
Dynamic Optical Cross-Connect: Channel switching
#1
l1
l11 , l12 , ... , l1M
#2
l21 , l12 , ... , lNM
l2
l21 , l22 , ... , l2M
#N
#1
#2
l11 , lN2 , ... , l2M
lM
lN1 , lN2 , ... , lNM
#N
lN1 , l22 , ... , l1M
Routing control
module
32
Lightwave Networks
Wavelength Conversion
l1 with data
Wavelength
Converter
l2 with data
l2 no data
(continuous-wave)
Resolve output contention of same wavelength from different input fibers
l1
l1
l1
l1
l-converter
l1 , l2
l2
output contention
33
Lightwave Networks
Common optical networks: SDH, SONET, FDDI
“All-Optical” Networks
 reduce number of O/E and E/O interfaces
 transparent to multiple signal format and bit rate
 facilitates upgrade and compatible with most existing electronics
 manage the enormous capacity on the information highway
 provide direct photonic access, add-drop and routing of broadband full
wavelength chunk of information
34
Lightwave Networks
35