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1 Optical Technologies and Lightwave Networks Outline:  Optical Technologies  Optical Fibers, Fiber Loss and Dispersion  Lightwave Systems and Networks.

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Presentation on theme: "1 Optical Technologies and Lightwave Networks Outline:  Optical Technologies  Optical Fibers, Fiber Loss and Dispersion  Lightwave Systems and Networks."— Presentation transcript:

1 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 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 nm)  suitable for long-distance transmission

3 3 Light Wave amplitudewavelength position/distance electromagnetic wave carry energy from one point to another travel in straight line described in wavelength (usually in  m or nm) speed of light in vacuum = 3  10 8 m/s

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

5 5 Optical Fiber cladding core light beam 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 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 FiberMulti-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 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 8 Fiber Attenuation low loss wavelength ranges: 1.3mm ( dB/km), 1.55mm ( dB/km)  suitable for telecommunications optical power of a signal is reduced after passing through a piece of fiber wavelength-dependent

9 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 10 Fiber Dispersion Standard Dispersion- flattened Dispersion- shifted Wavelength (  m) Dispersion (ps/(kmnm)) Typical values: standard fiber: ~ 0 ps/(km nm ~17 ps /(km nm dispersion-shifted fiber: ~0.5 ps /(km nm

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

12 12 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) Laser Source and Photodetector Photodetector convert incoming photons into electric current (photo-current) input electric current output optical power threshold current optical power (photons) photo-current optical power (photons) Input electrical data wavelength

13 13 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 A2A1 A C B B2B1 C2C1 B1A1C2B2A2C1 time

14 14 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 A C B freq fAfA fBfB fCfC f A f B f C

15 15 Multiplexing Schemes Wavelength Division Multiplexing (WDM) 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 wavelength spacing: 0.8 nm (100-GHz) A C B wavelength A B C wavelength multiplexer A B C

16 16 Multiplexing Schemes Hybrid Types (TDM/WDM, SCM/WDM)  higher capacity A C B wavelength A B C wavelength multiplexer f1f2f3f1f2f3 f1f2f3f1f2f3 f1f2f3f1f2f3 SCM/WDM A C B wavelength A B C wavelength multiplexer TDM stream TDM/WDM A A  C B C

17 17 Transmission System Capacity 132 Ch 1 Ch TDM

18 18 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 ( nm) (mature and widely deployed nowadays) Pr 3+ or Nd 3+ doped fiber amplifier: operates at 1310 nm transmission window (not very mature) ultra-wideband EDFA: S-band ( nm), C-band ( nm), L-band ( nm) G

19 19 Lightwave Systems  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 Traditional Optical Fiber Transmission System E MUXE MUX XMTR REG RPTR RCVR REG RPTR EDMUXEDMUX Low-Rate Data In Low-Rate Data Out DET EQDEC TMG REC LASER AMP Opto-Electronic Regenerative Repeater

20 20 Lightwave Systems  Multi-channel WDM operation  Transparent data-rate and modulation form  One optical amplifier (per fiber) supports many channels  km amplifier spacing  Distortion and noise accumulate  Graceful growth Optical Fiber Transmission System O MUXO MUX ODMUXODMUX Data InData Out OA XMTR 1 2 N RCVR 1 2 N

21 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 22 Undersea Fiber Systems AT&T

23 23 Undersea Fiber Systems SYSTEMTIMEBANDWIDTH/NUMBER OF COMMENTS BIT-RATE BASIC CHANNELS TAT-1/21955/590.2 MHz48 HAW-11957COPPER COAX TAT-3/41963/65ANALOG HAW MHz140VACUUM TUBES H-G-J1964 TAT HAW MHz840Ge TRANSISTORS H-G-O1975 TAT-6/71976/8330 MHz4,200Si TRANSISTORS TAT-81988OPTICAL FIBER HAW Mb/s8,000DIGITAL TPC = 1.3  m TAT ,000 TPC Mb/s24,000 = 1.55  m TAT-10/111992/93 TAT Gb/s122,880OPTICAL AMPLIFIERS TPC = 1.55  m TAT: Trans-Atlantic Telecommunications TPC: Trans-Pacific Cable

24 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 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 26 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) Headend electrical repeater Remote Node Fiber Coaxial Cable Passive Optical Network (PON) passive optical splitter

27 27 Lightwave Broadband Access WDM-PON: Wavelength Division Multiplexed Passive Optical Network use multiple wavelengths, each serves a certain group of users higher capacity Headend electrical repeater Remote Node multi-wavelength source 1 2 N-1 N 1, …, N WDM-PON wavelength demultiplexer

28 28 Lightwave Networks  Transmission  Multi-access  Channel add-drop  Channel routing/ switching

29 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 Lightwave Networks connection between two hosts via a channel  need to access channel Channel: Wavelength (in WDM network), Time Slot (in TDM network) TRTRTRTR A B C D

30 30 Lightwave Networks Add-drop Multiplexer (ADM) 1, 2, 3 1, 2 *, * ADDDROP ADD 1 N 1 1 * 1,..., N 1 *,..., N Wavelength ADM: Channel add-drop

31 31 Lightwave Networks Static Optical Cross-Connect : Channel routing 11, 12, 13, …, 1M 21, 22, 23, …, 2M 31, 32, 33, …, 3M N1, N2, N3, …, NM N1, …, 3(N-2), 2(N-1), 1N 31, 22, 13, N4,... 21, 12, N3, …, 3N 11, N2, …, 3(N-1), 2N (fixed wavelength routing pattern)

32 32 #1 #N #2 #1 #2 #N Routing control module 11,  2   M  1,  2   M  1,  2   M  1,  2   M  1,  2   M  1,  2   M 1 2 M Lightwave Networks Dynamic Optical Cross-Connect : Channel switching

33 33 Lightwave Networks Wavelength Conversion Wavelength Converter 1 with data 2 no data (continuous-wave) 2 with data Resolve output contention of same wavelength from different input fibers converter 2 1, 2 output contention

34 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 35 Lightwave Networks


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