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IP-ADMAT, 19.05.2005 Light Guides1
Konrad Mertens,
Lab for Optoelectronics and Sensors
Department of Electrical Engineering and Computer Science
Münster University of Applied Sciences
Basics and Applications of Light Guides
What the hell the data highway is made of?
IP-ADMAT, 19.05.2005 Light Guides2
1) Historical review
2) Why fibers for communication?
3) Principles of light guidance
4) Attenuation
5) Fiber types
6) Components of fiber communication systems
7) Real fiber systems
Outline
IP-ADMAT, 19.05.2005 Light Guides3
- before time:
- end of 18th cent.: bar telegraph
- 1960: first laser (rubine)
1962: first semiconductor laser (heavily cooled)
1970: first semiconductor laser (room temp.)
- 1970ies: low loss glass fibers (Corning Glas)
- 1980ies: fibers in wide distance networks
- 1990ies: fibers in city networks
- since 1995: penetration of fibers in local area networks
1) Historical Review
IP-ADMAT, 19.05.2005 Light Guides4
Bartelegraph of Monsieur Chappé
- 96 different signs
- e.g. Paris-Lille: 2 min
IP-ADMAT, 19.05.2005 Light Guides5
2) Why fibers for communication?
- low attenuation
- high bandwidth
- thin and flexible
- no electromagnetic emmissions (sidetalk)
- no electromagnetic immissions (e.g. from generators etc.)
- isolation of potentials between transmitter and receiver
Advantages:
IP-ADMAT, 19.05.2005 Light Guides6
Comparison of attenation: copper cable fiber
copper: attenuation rises dramatically at higher data rates
fibers: attenuation is independent of data rate
fibers
coaxial cable
twisted pair
copper cable:
Mbit/s
R L
C
data rate
IP-ADMAT, 19.05.2005 Light Guides7
Comparison: copper cable fiber cable
Example: Wide distance cable between Münster and Hamburg (300 km)
Capacity: 100.000 phone calls (6.4 Gbit/s)
copper
cable
fiber
cable
5 kg/m
300 g/m
Ø 8 cm
Ø 2 cm
100 amplifiers necessary
no amplifiers necessary
IP-ADMAT, 19.05.2005 Light Guides8
- often still more expensive
- contacting is “special”
- special components are necessary (optical transmitters and receivers)
- special devices (measurement etc.) are necessary
- lack of knowledge of engineers and technicians
Disadvantages of fibers versus copper caples
IP-ADMAT, 19.05.2005 Light Guides9
3) Principle of light guidance
Principle of total reflection:
critical angle of total reflection:
e.g. glas/air: n = 1,5 / 1 -> 1t = 42
n1 sin 1 = n2 sin 2
1t = arcsin (n2 /n1)
Law of refraction:
n2
n1
2
1
n1 > n2
IP-ADMAT, 19.05.2005 Light Guides10
Light guidance in fibers
n2
n1
- refractive index n1 must be larger than n2
- light ist guided in the core through repeated total reflection
- light „sees“ an „inner mirrored pipe“
- if the incidence angle is too large, light will be radiated
Coating (SiO2)
Core (SiO2 with doped Ge)
IP-ADMAT, 19.05.2005 Light Guides11
4) Attenuation in fibers
in dB/km
Rayleigh-scattering
attenuation coefficient
0
2
4
6
OH - Absorption
in nm800 1000 1200 1400 1600850 nm
1. window1300 nm
2. window1550 nm
3. window
5
3
1
14
IP-ADMAT, 19.05.2005 Light Guides12
Example
Power P1 P2
L = 10 km
Fiber with attenuation coefficient dB/km
Attenuation A = · L = 0,3 dB/km · 10 km = 3 dB
This means: half of the Power is still there!
Compare this to copper cable: L50% = 30 m
Compare this to window glass: L50% = 3 cm
IP-ADMAT, 19.05.2005 Light Guides13
5) Fiber Types I: Multimode - Fibers
a) Step index fiber: refractive index n(r) has a step
n(r)
n2
n1
radius n2
n1
incoming impulse: outcoming impulse:
- Broadening of the pulse „Dispersion“:
only low data rates are possible
d = 50 m
this fiber is rarely used
IP-ADMAT, 19.05.2005 Light Guides14
b) Graded index fiber: n(r) changes smoothly
n(r)
n2
n1
r n2
n1max
incoming impulse: outcoming impulse:
- The outer light rays run fasterFree space velocity c
Refractive index n(velocity v = )
much less pulse broadening!
IP-ADMAT, 19.05.2005 Light Guides15
Fiber Types II: Singlemode - Fibers
Idea: Lets build a fiber where only one „mode“ matches in
1.: small core ( d = 10 m)
2.: small refractive index step
Measures:
n2
n(r)
r n2
n1
incoming impulse: outcoming impulse:
d = 10 m
That´s it!
n1
IP-ADMAT, 19.05.2005 Light Guides16
Singlemode versus Multimode - Fiber
Monomode-fibers offer: - large bandwidths (e.g. 100 Gbit/s)
- low attenuation
but: - light injection is difficult
- laser diodes are necessary
We use them for high data rates and long distances
In local area regime multimode fibers dominate (still…)
IP-ADMAT, 19.05.2005 Light Guides17
6) Optical Communication Systems
Principle:
electricalsignal
electricalsignal
opticalsignal
fiber
opticaltransmitter
opticalreceiver
We need: - optical transmitter: LED or laserdiode
- optical receiver: photodiode
- connectors, etc.
IP-ADMAT, 19.05.2005 Light Guides18
Optical Transmitters
Light emitting diodes (LED)
n
p
+
-
construction: example:
+ cheap
- small power
- only for multimode fibers
properties:
Laser diodes (LD)
construction: example: properties:
n
pi
-
+
+ high power
+ suitable for single mode fibers
- expensive
- easily damaged
IP-ADMAT, 19.05.2005 Light Guides19
Optical Receivers
Photo diodes
1. optical Window: (850 nm): Silicon (cheap)
2. + 3. optical window (1300, 1550 nm): Ge or InP (expensive)
construction: example:
p+
n
-+
Licht
Materials:
IP-ADMAT, 19.05.2005 Light Guides20
Connecting fibers
electrode
light arc
cladding
fiber coating
fiber core
automatic position control
a) fiber connectors:
b) fiber splicing:
connectormating adaptor connectormating adaptor
electrode
IP-ADMAT, 19.05.2005 Light Guides21
7) Real Fiber Systemsa) Wide Area Networks (WAN)
Technology: Wavelength division multiplexing (WDM)
Prism, n= f()
Receiv. 2
fiber
Principle:
Laser 1
Laser 2
Spectrum:
P()
Receiv. 1
1300 1400 1500 1600 1700
0,2
0,4
0,6
100 nm
attenuation
nm
e.g.: channel separation of 0,8 nm: more than 100 channels possible
dB/km
IP-ADMAT, 19.05.2005 Light Guides22
Example for Wide Area Connections: transatlantic cable TAT-14
- two cables in separate routes
- each cable contains 8 fibers
- every fiber transports 16 wavelength channels (wavelength division multiplexing)
- every of the 16 lasers has a data rate of 10 Gbit/s
Total capacity: 640 Gbit/s 10 Mill. simultaneous phone calls!!
IP-ADMAT, 19.05.2005 Light Guides23
b) Metropolitan Area Networks (MAN)
e.g. Fiber Double Ring (10 Gbit/s)
155 Mbit/sPhone call
swiching
cross-connector
10 Gbit/s
company
network
to next city
10 Gbit/s
+ flexible
+ fail-safe
cross-connector
cross-connector
cross-connector
cross-connector
cross-connector
„last mile“
IP-ADMAT, 19.05.2005 Light Guides24
c) Local Area Networks (LAN)
classic: 10 Mbit/s
Fast Ethernet: 100 Mbit/s
Gigabit Ethernet: 1000 Mbit/s = 1 Gbit/s
10G Ethernet: 10.000 Mbit/s = 10 Gbit/s
e.g.: Ethernet:
Hub
SwitchHost
Host
Host HostPC
PC
PC
PC
Work-
station
fibers
copper
In the next five years fibers will reach the end user!
IP-ADMAT, 19.05.2005 Light Guides25
Conclusions
Fibers have significant advantages against copper cables
Technologies are there to use them in wide, mid and local range
Fibers will penetrate even the “last mile”
Only fibers make the “data highway” possible
IP-ADMAT, 19.05.2005 Light Guides26
Production of fibers:
1) Preform production (e.g. OVD: Outside Vapour Deposition):
2) Pulling of the fiber:
Substrate rod
a) Growing on: b) Tempering:
SiCl4 GeCl4
Rußschicht
c) Collapse
1500 °C 2000 °C
Preform:Length: ca. 1 m
Diam.: ca. 2 cm
regulation
Take-up reel
Pulling velocity: ca. 300 m/min
IP-ADMAT, 19.05.2005 Light Guides27
“normal” Repeater:
Erbium-doped Fiber
Pump-Laser
Advantages:
no opt./electr. and electr./opt. conversion necessary
multiple bitstreams on different wavelenghts can be amplified
Optical Fiber Amplifiers
Optical Amplifier:
= 1550 nm = 1550 nm
= 1480 nm
Prinziple:Excitiation:
E2
E1
Stimulated Emission:
E2
E1
Amplification Curve:
= 1480 nm
= 1550 nm
25 dB
15501540 15601530 nm
IP-ADMAT, 19.05.2005 Light Guides28
BT 1
BT 2
BT 3
BT 4
BT 5
Gigabit/Switch100 Mbit/s
50 Mbit/s
Wohnheim
Laserzentrum BT19 / Mensa BT11 BT12
STM-1(155 Mbit/s)
MS
BT 8
BT 6/7 BT 6/7
Bürgerkamp HGI
Multimodefaser mit 1 Gbit/s
Singlemodefaser mit 1 Gbit/s
Twisted Pair mit 100 Mbit/s
• An jedem Switch: 24 oder 48 Kupferanschlüsse (100 Mbit/s) zu den Laboren
• Parallel zu jeder MMF eine zweite Backup-MMF mit 100 Mbit/s
zu den Laboren
3
2
10
4 2
9
226
54 6
IP-ADMAT, 19.05.2005 Light Guides29
Ethernet-Standards mit LWL
Standard-Ethernet: 10 Base F: - 10 Mbit/s, Lmax = 2000 m
- Multimode-Fasern, LEDs, = 850 nm,
Fast-Ethernet: 100 Base FX - 100 Mbit/s, Lmax = 400 m
- Multimode-Fasern, LEDs, = 1300 nm
Gigabit-Ethernet: a) 1000 BaseSX: -1000 Mbit/s, Lmax = 550 m,
- Multimode-Fasern, Laserdioden, = 850 nm,
b) 1000 BaseLX: - 1000 Mbit/s, Lmax = 5000 m,
- Monomode-Fasern, Laserdioden, = 1300 nm
10G-Ethernet: 10G Base E (z.B.): - 10 Gbit/s, Lmax = 40 km
- Monomode-Fasern, Laserdioden, = 1550 nm
IP-ADMAT, 19.05.2005 Light Guides30
Übersicht: Einsatz von Glasfasern
Distanz Datenrate Fasertyp
bis 50 m
bis 2 km
bis 20 km
> 20 km
bis 100 kBit/s
bis 10 Mbit/s
bis 100 Mbit/s
> 100 Mbit/s
Kunststoffaser
Multimode-Gradientenfaser
Multimode-Gradientenfaseroder Monomodefaser
Monomodefaser