1 / 35

Optical Technologies and Lightwave Networks

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. Need for Optical Technologies.

illana-combs
Download Presentation

Optical Technologies and Lightwave Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. 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

  3. amplitude position/distance wavelength Light Wave • 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

  4.  >   > c Incident light Reflected light  Medium 1   Medium 2   Reflecting surface  Reflection and Refraction of Light Reflection Refraction • 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 Incident angle= reflected angle

  5. cladding light beam core Optical Fiber • 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

  6. 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 • allow only one fiber mode • typical value: 9/125mm • larger core diameter • allow more than one fiber modes • typical value: 62.5/125mm

  7. 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

  8. 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

  9. 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

  10. 20 10 0 -10 -20 Standard Dispersion-flattened Dispersion (ps/(km•nm)) Dispersion-shifted 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Wavelength (mm) Fiber Dispersion Typical values: standard fiber: ~ 0 ps/(km• nm) @1300 nm ~17 ps /(km• nm) @1550 nm dispersion-shifted fiber: ~0.5 ps /(km• nm) @1550 nm

  11. System Capacity • fiber attenuation  loss in optical power limit transmission distance • fiber dispersion  pulse broadening  limit transmission bit-rate

  12. Input electrical data optical power (photons) output optical power wavelength l input electric current threshold current optical power (photons) photo-current Laser Source and Photodetector • Laser source • generate laser of a certain wavelength • made of semiconductors • output power depends on input electric current • need temperature control to stabilize the output power and output wavelength (both are temperature dependent) • Photodetector • convert incoming photons into electric current (photo-current)

  13. A2 A2 C2 B2 B1 C2 C1 A1 A1 C1 B1 B2 A time B l C Multiplexing Schemes Multiplexing: transmits information for several connections simultaneously on the same optical fiber Time Division Multiplexing (TDM) • 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

  14. fA fB fC fA freq freq A fB freq B fC l freq C Multiplexing Schemes Subcarrier Multiplexing (SCM) • multiple frequency carriers (subcarriers) are combined together • only require one wavelength (one laser) (optical carrier) • suitable for video distribution on fiber

  15. lA lA lB lC A lB wavelength B lC C wavelength multiplexer Multiplexing Schemes Wavelength Division Multiplexing (WDM) wavelength spacing: 0.8 nm (100-GHz) • one distinct wavelength (per laser) per sender • 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

  16. TDM/WDM lA lB lC lA lB lC SCM/WDM f1 f2 f3 f1 f2 f3 f1 f2 f3 wavelength wavelength TDM stream A A TDM stream B B TDM stream C C wavelength multiplexer wavelength multiplexer Multiplexing Schemes Hybrid Types (TDM/WDM, SCM/WDM)  higher capacity lA lA lB lB lC lC

  17. 132 Ch 1 Ch TDM Transmission System Capacity

  18. G Optical Amplifier • 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)

  19. Low-Rate Data Out Low-Rate Data In E MUX E D MUX REG RPTR REG RPTR XMTR RCVR Opto-Electronic Regenerative Repeater EQ DEC LASER DET AMP AMP TMG REC Lightwave Systems Traditional Optical Fiber Transmission System • 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

  20. Data In Data Out O MUX O D MUX l1 l1 XMTR l2 RCVR l2 XMTR RCVR OA OA OA lN XMTR lN RCVR Lightwave Systems Optical Fiber Transmission System • 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

  21. 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

  22. Undersea Fiber Systems AT&T

  23. SYSTEM TIME BANDWIDTH/ NUMBER OF COMMENTS BIT-RATE BASIC CHANNELS TAT-1/2 1955/59 0.2 MHz 48 HAW-1 1957 COPPER COAX TAT-3/4 1963/65 ANALOG HAW-2 1964 1.1 MHz 140 VACUUM TUBES H-G-J 1964 TAT-5 1970 HAW-3 1974 6 MHz 840 Ge TRANSISTORS H-G-O 1975 TAT-6/7 1976/83 30 MHz 4,200 Si TRANSISTORS TAT-8 1988 OPTICAL FIBER HAW-4 1989 280 Mb/s 8,000 DIGITAL TPC-3 1989 l = 1.3 mm TAT-9 1991 16,000 TPC-4 1992 560 Mb/s 24,000 l = 1.55 mm TAT-10/11 1992/93 TAT-12 1995 5 Gb/s 122,880 OPTICAL AMPLIFIERS TPC-5 1995 l = 1.55 mm TAT: Trans-Atlantic Telecommunications TPC: Trans-Pacific Cable Undersea Fiber Systems

  24. 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)

  25. 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

  26. Passive Optical Network (PON) Remote Node passive optical splitter electrical repeater Headend Coaxial Cable Fiber Lightwave Broadband Access • 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)

  27. WDM-PON Remote Node l1 l1, … , lN l2 electrical repeater Headend lN-1 multi-wavelength source lN wavelength demultiplexer Lightwave Broadband Access • WDM-PON: Wavelength Division Multiplexed Passive Optical Network • use multiple wavelengths, each serves a certain group of users • higher capacity

  28. Transmission • Multi-access • Channel add-drop • Channel routing/ switching Lightwave Networks Optical Networks

  29. Tunable transmitter and tunable receiver (TTTR) • most flexible, expensive • Fixed transmitter and tunable receiver (FTTR) • 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) • each node receives data on a fixed channel • transmitter is tuned to the receiving channel of the destination node before sending data T T T T R R R R Lightwave Networks • connection between two hosts via a channel  need to access channel • Channel: Wavelength (in WDM network), Time Slot (in TDM network) A B C D

  30. l1, l2, l3 l1, l2*, l3 Add-drop Multiplexer (ADM) l2 l2* DROP ADD l1 l1, ..., lN l1*, ..., lN lN l1* l1 Lightwave Networks Channel add-drop Wavelength ADM: ADD DROP

  31. 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 Lightwave Networks Static Optical Cross-Connect: Channel routing (fixed wavelength routing pattern)

  32. l1 #1 #1 l11 , l12 , ... , l1M l21 , l12 , ... , lNM l2 #2 #2 l21 , l22 , ... , l2M l11 , lN2 , ... , l2M lM #N #N lN1 , lN2 , ... , lNM lN1 , l22 , ... , l1M Routing control module Lightwave Networks Dynamic Optical Cross-Connect: Channel switching

  33. l1 with data l2 with data Wavelength Converter l2 no data (continuous-wave) l1 l1 l1 l1 l2 l-converter Lightwave Networks Wavelength Conversion Resolve output contention of same wavelength from different input fibers l1 , l2 output contention

  34. 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

  35. Lightwave Networks

More Related