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Konrad Mertens, Lab for Optoelectronics and Sensors

Basics and Applications of Light Guides. What the hell the data highway is made of?. Konrad Mertens, Lab for Optoelectronics and Sensors Department of Electrical Engineering and Computer Science Münster University of Applied Sciences. Outline. Historical review

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Konrad Mertens, Lab for Optoelectronics and Sensors

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  1. Basics and Applications of Light Guides What the hell the data highway is made of? Konrad Mertens, Lab for Optoelectronics and Sensors Department of Electrical Engineering and Computer Science Münster University of Applied Sciences IP-ADMAT, 19.05.2005 Light Guides 1

  2. Outline • Historical review • Why fibers for communication? • 3) Principles of light guidance • 4) Attenuation • 5) Fiber types • 6) Components of fiber communication systems • 7) Real fiber systems IP-ADMAT, 19.05.2005 Light Guides 2

  3. 1) Historical Review • - 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 IP-ADMAT, 19.05.2005 Light Guides 3

  4. Bartelegraph of Monsieur Chappé - 96 different signs - e.g. Paris-Lille: 2 min IP-ADMAT, 19.05.2005 Light Guides 4

  5. 2) Why fibers for communication? Advantages: • - 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 IP-ADMAT, 19.05.2005 Light Guides 5

  6. Comparison of attenation: copper cable  fiber copper cable: R L twisted pair  C coaxial cable fibers Mbit/s data rate • copper: attenuation rises dramatically at higher data rates • fibers: attenuation is independent of data rate IP-ADMAT, 19.05.2005 Light Guides 6

  7. Comparison: copper cable  fiber cable • Example: Wide distance cable between Münster and Hamburg (300 km) • Capacity: 100.000 phone calls (6.4 Gbit/s) 5 kg/m 100 amplifiers necessary copper cable Ø 8 cm 300 g/m no amplifiers necessary fiber cable Ø 2 cm IP-ADMAT, 19.05.2005 Light Guides 7

  8. Disadvantages of fibers versus copper caples • - 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 IP-ADMAT, 19.05.2005 Light Guides 8

  9. 3) Principle of light guidance Law of refraction: n1 sin a1 = n2 sin a2 a2 n2 n1 n1 > n2 a1 Principle of total reflection: critical angle of total reflection: e.g. glas/air: n = 1,5 / 1 -> a1t = 42 a1t = arcsin (n2 /n1) IP-ADMAT, 19.05.2005 Light Guides 9

  10. Light guidance in fibers Coating (SiO2) Core (SiO2 with doped Ge) 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 IP-ADMAT, 19.05.2005 Light Guides 10

  11. 1  l4 4) Attenuation in fibers attenuation coefficient  6 5 Rayleigh-scattering 4 OH - Absorption in dB/km 3 2 1 0 lin nm 800 1000 1200 1400 1600 850 nm 1. window 1300 nm 2. window 1550 nm 3. window IP-ADMAT, 19.05.2005 Light Guides 11

  12. Example L = 10 km Power P1 P2 Fiber with attenuation coefficient a = 0,3 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 Guides 12

  13. 5) Fiber Types I: Multimode - Fibers a) Step index fiber: refractive index n(r) has a step radius n2 n1 n2 n1 n(r) d = 50 mm incoming impulse: outcoming impulse: - Broadening of the pulse „Dispersion“: only low data rates are possible this fiber is rarely used IP-ADMAT, 19.05.2005 Light Guides 13

  14. Free space velocity c - The outer light rays run faster (velocity v = ) Refractive index n much less pulse broadening! b) Graded index fiber: n(r) changes smoothly n2 r n1max n2 n1 n(r) incoming impulse: outcoming impulse: IP-ADMAT, 19.05.2005 Light Guides 14

  15. Fiber Types II: Singlemode - Fibers Idea: Lets build a fiber where only one „mode“ matches in Measures: 1.: small core ( d = 10 mm) 2.: small refractive index step n2 r n1 n2 n1 n(r) d = 10 mm incoming impulse: outcoming impulse: That´s it! IP-ADMAT, 19.05.2005 Light Guides 15

  16. 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 Guides 16

  17. 6) Optical Communication Systems Principle: optical signal optical transmitter optical receiver fiber electrical signal electrical signal We need: - optical transmitter: LED or laserdiode - optical receiver: photodiode - connectors, etc. IP-ADMAT, 19.05.2005 Light Guides 17

  18. + p i n - Optical Transmitters Light emitting diodes (LED) construction: example: properties: + + cheap - small power - only for multimode fibers p n - Laser diodes (LD) construction: example: properties: + high power + suitable for single mode fibers - expensive - easily damaged IP-ADMAT, 19.05.2005 Light Guides 18

  19. Optical Receivers Photo diodes construction: example: Licht p+ + - n Materials: 1. optical Window: (850 nm): Silicon (cheap) 2. + 3. optical window (1300, 1550 nm): Ge or InP (expensive) IP-ADMAT, 19.05.2005 Light Guides 19

  20. Connecting fibers a) fiber connectors: mating adaptor connector mating adaptor connector b) fiber splicing: cladding electrode fiber coating fiber core automatic position control light arc electrode IP-ADMAT, 19.05.2005 Light Guides 20

  21. 7) Real Fiber Systems a) Wide Area Networks (WAN) Technology: Wavelength division multiplexing (WDM) Principle: Prism, n= f(l) l Laser 1 1 fiber Laser 2 l Receiv. 2 2 Receiv. 1 Spectrum: attenuation a dB/km 0,6 P() 0,4 100 nm 0,2 l l l1 l2 nm 1300 1400 1500 1600 1700 • e.g.: channel separation of 0,8 nm: more than 100 channels possible IP-ADMAT, 19.05.2005 Light Guides 21

  22.  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 Guides 22

  23. b) Metropolitan Area Networks (MAN) e.g. Fiber Double Ring (10 Gbit/s) to next city cross-connector „last mile“ cross-connector 155 Mbit/s cross-connector cross-connector Phone call swiching 10 Gbit/s cross-connector cross-connector 10 Gbit/s company network + flexible + fail-safe IP-ADMAT, 19.05.2005 Light Guides 23

  24. c) Local Area Networks (LAN) e.g.: Ethernet: 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 fibers Work- station copper Host PC Switch PC Hub PC Host PC Host Host In the next five years fibers will reach the end user! IP-ADMAT, 19.05.2005 Light Guides 24

  25. 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 Guides 25

  26. Production of fibers: 1) Preform production (e.g. OVD: Outside Vapour Deposition): a) Growing on: b) Tempering: c) Collapse 2000 °C 1500 °C Preform: Length: ca. 1 m Diam.: ca. 2 cm Rußschicht Substrate rod GeCl4 SiCl4 2) Pulling of the fiber: regulation Take-up reel Pulling velocity: ca. 300 m/min IP-ADMAT, 19.05.2005 Light Guides 26

  27. Optical Fiber Amplifiers “normal” Repeater: Optical Amplifier: Excitiation: Prinziple: E2 l = 1480 nm E1 Erbium-doped Fiber Stimulated Emission: l = 1550 nm l = 1550 nm Pump-Laser E2 l = 1550 nm l = 1480 nm E1 Amplification Curve: 25 dB Advantages: • no opt./electr. and electr./opt. conversion necessary • multiple bitstreams on different wavelenghts can be amplified 1530 1540 1550 1560 nm IP-ADMAT, 19.05.2005 Light Guides 27

  28. 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 Laserzentrum BT19 / Mensa BT11 BT12 BT 1 3 2 2 6 BT 2 BT 8 BT 3 9 2 MS Gigabit/Switch 100 Mbit/s BT 4 STM-1 (155 Mbit/s) 50 Mbit/s 10 Wohnheim 4 2 BT 5 5 BT 6/7 BT 6/7 4 6 zu den Laboren Bürgerkamp HGI IP-ADMAT, 19.05.2005 Light Guides 28

  29. Ethernet-Standards mit LWL • Standard-Ethernet: 10 Base F: - 10 Mbit/s, Lmax = 2000 m • - Multimode-Fasern, LEDs, l = 850 nm, • Fast-Ethernet: 100 Base FX - 100 Mbit/s, Lmax = 400 m • - Multimode-Fasern, LEDs, l = 1300 nm • Gigabit-Ethernet: a) 1000 BaseSX: -1000 Mbit/s, Lmax = 550 m, • - Multimode-Fasern, Laserdioden, l = 850 nm, • b) 1000 BaseLX: - 1000 Mbit/s, Lmax = 5000 m, • - Monomode-Fasern, Laserdioden, l = 1300 nm • 10G-Ethernet: 10G Base E (z.B.): - 10 Gbit/s, Lmax = 40 km • - Monomode-Fasern, Laserdioden, l = 1550 nm IP-ADMAT, 19.05.2005 Light Guides 29

  30. Übersicht: Einsatz von Glasfasern IP-ADMAT, 19.05.2005 Light Guides 30

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