TCOM 503 Fiber Optic Networks

1. TCOM 503Fiber Optic Networks Spring, 2007 Thomas B. Fowler, Sc.D. Senior Principal Engineer Mitretek Systems

2. Course overview • This course, together with TCOM 513, presents basic material needed to understand optical communications • Physical principles of optical devices and networks • Components of fiber optic systems and how they function • Light as a communications medium: modulation, noise, detection of signals • How these components work together to create useful fiber optic networks • How fiber optic networks are used to create large-scale communications networks • How to buy optical communications products and services • How all-optical networks will function, and their advantages and problems

3. Course goal • Impart general background on optical communications • Enable students to undertake more detailed study of any aspect of optical communications • Give enough information so that students become informed consumers and decision makers on many optical communications issues

4. Course organization • 7 weeks • Main text: Understanding Optical Communications, Harry Dutton, Prentice-Hall, 1998 • Supplementary text: Fiber Optic Communications, 4th Edition, Joseph C. Palais, Prentice-Hall, 1998 • Other material to be downloaded from Internet (see syllabus) • Student evaluation • Homework 40% • Project outline 20% • Final exam 40%

5. Topics for TCOM 503 • Week 1: Overview of fiber optic communications • Week 2: Brief discussion of physics behind fiber optics • Week 3: Light sources for fiber optic networks • Week 4: Fiber optic components fabrication and use • Week 5: Modulation of light, its use to transmit information • Week 6: Noise and detection • Week 7: Optical fiber fabrication and testing of components

6. Week 1: Overview of fiber optic communications • Basics of communications systems • Fiber optic networks compared to other networks • Advantages of and drivers for optical networks • Architecture of typical fiber optic networks • Brief history of optical networking • Fiber optic network terminology • General communications systems background

7. What is purpose of communications system? • To transfer information from one location to another • Voice • Data • Video • Audio • Desirable attributes • Fast • Accurate • Secure • Scalable • Routable/switchable • Capable of handling multiple types of information (data) • Cheap

8. Components of a telecommuncations system—physical view Link Modulator/ transmitter Receiver/ demodulator Source Encoder Decoder Receiver Cable Microwave Other wireless Light Smoke signals

9. Components of a telecommuncations system—logical view Source Interface Interface Receiver Packet-switched network

10. What is optical networking? • Use of optical components in place of electronic components in a network environment • Light waves (including infrared) as a medium for the transmission or switching of data • Pure optical or all-optical networks use light exclusively from end to end • Most commonly, optical elements (optical fiber, optical amplifiers) are used in transmission links • Known as opto-electronic networks (OEO) • Switching still done electronically (“in silicon”) • No pure optical networks at present • All-optical switching is a laboratory project at present, though opto-mechanical systems exist which use flipping mirrors

11. What is optical networking? (continued) • Long-term goal is the all-optical network, with all switching, transmission, and routing done optically • Conversion to/from electrical signals occurs only at boundary • Likely to be commercialized within 5 years

12. How are optical networks different? • Optical networks differ from conventional electronic or “wireline” networks • Rely upon light waves to carry data, rather than electron-based transmission in wires • Differ from conventional wireless networks • Operate at much higher frequencies • Hundreds of terahertz vs. 30 GHz • Wavelength (l) of 1600 nm ~ 188 THz • Use waveguides (in the form of optical fiber) to carry the data-bearing waves.

13. Optical and electronic networks Optical Electronic Wireless

14. Advantages Cost-effective bandwidth Noise isolation Security Smaller physical presence Readily upgradable Drivers Demand for bandwidth Commoditization of optical networking components Reduced number of components Shorter service contracts Promise of rapid provisioning Why optical networks?

15. Advantages • Cost-effective bandwidth • Above a certain threshold price per unit of bandwidth is lower • For very high bandwidths (~Gbit/second and higher) and even relatively short distances (~100 m), optical fiber is usually the only practical choice • Noise isolation • Optical fibers are not affected by electrical noise-producing sources • Can be used in environments where adequate shielding of electrical cables would be difficult or impossible • Only in environments with high levels of radioactivity is there a potential problem

16. Advantages (continued) • Greater security • Optical fiber does not emit electromagnetic radiation which can be intercepted • Much more secure than many other types of wiring, such as category 5 untwisted pair used for Ethernet applications • Tapping optical fiber is also much more difficult • Smaller physical presence • Single optical fiber cable with a diameter of less than 6 mm can replace a bulky cable with hundreds of wires • Critical in applications where space is at a premium • Ships and aircraft • Retrofitting buildings and rewiring cities, where space in conduits may also be very limited

17. Advantages (continued) • Ready upgrade path • Constant improvements to fiber optic cable itself • In most cases, increased bandwidth can be had by installing new optical multiplexing equipment

18. Disadvantages • Higher cost per meter • Greater difficulty in splicing and maintenance • Technicians need to be retrained • Need to convert optical signals back to electronic signals for processing

19. Supply • Exuberance of late 90s and early 2000s led to huge volumes of fiber put in the ground • New technologies mean more bandwidth even from existing fibers

20. Drivers • Huge and insatiable demand for bandwidth—cooled after dot com crash • May have been hyped all along • But developments such as more video on Internet and anticipated use of Internet for video delivery in future will require optical connections to or close to homes • Commoditization of optical network components enables more powerful and economical networks to be built • Reduced number of components means network simplification and equipment consolidation • Shorter service contracts implies faster depreciation and more rapid replacement of equipment with newer technology

21. Relative cost per DS3 (45 mbit/sec) mile PPN=Purely Photonic Networks Source:Qtera Networks/NGN99

22. Evolution of optical networks Source: Sycamore Networks/NGN 99

23. Problems with end-end all-optical networks • Physical limitations of devices still limit scalability and performance of optical networks • Multi-vendor environment and rapidly evolving technology limits plug-and-play compatibility • Subnetworks are easier to monitor and manage • Current action in area of Passive Optical Networks (PONs) and Fiber-to-the-X (FTTx) • Many small vendors working in optical switch area: Calient, Chromux, Continuum, Dicon, Engana GlimmerGlass, Lambda Optical Systems, Lynx Photonic Networks, MEMX, and Polatis

24. All-optical networks • Typical application

25. Optical network capacity vs. distance

26. l1 end user services end user services SONET D W D M SONET D W D M end user services end user services SONET SONET ln Schematic diagram of typical optical network today Modulator/ transmitter Receiver/ demodulator Source Encoder Decoder Receiver Link Source: Sycamore Networks/NGN 99

27. Simplified optical network with ring architecture Source: Tektronix

28. History of optical communications systems • Glass invented, c. 2500 BC • Fires have been used for signaling since Biblical times • Famous opening of Aeschylus’ play Agamemnon (c. 458 BC): I wait; to read the meaning in that beacon light,a blaze of fire to carry out of Troy the rumorand outcry of its capture…. • Smoke signals have also been used for thousands of years, most notably by Native Americans • Lanterns in Boston’s Old North Church used to signal Paul Revere on his famous ride (1775) • Flashing lights used on ships for communication since time of Lord Nelson (1758-1805)

29. History of optical communications systems (continued) • Optical telegraph built in France during 1790s by Claude Chappe • Signalmen occupied a series of towers between Paris and Lille, 230 km • Signals relayed using movable signal arms • 15 minutes to send a message • In 1840, Daniel Colladon demonstrated light guiding in jet of water in Geneva • Used in opera Faust, 1853, by Paris Opera • In 1870, John Tyndall demonstrated principle of guiding light through internal reflections, using a jet of pouring water (duplicating Colladon’s work) • In 1880, Alexander Graham Bell patented photophone, which utilizes unguided light bounced off of vibrating mirrors to carry speech • Intended for long distance • Didn’t work in cloudy weather

30. History of optical communications systems (continued) • Also in 1880, William Wheeler invented system of light pipes to direct light around homes • Pipes lined with a highly reflective coating • Single electric arc lamp placed in the basement • In 1888, first use of bent glass rods to illuminate body cavities (medical team of Roth and Reuss of Vienna) • In 1895, early attempt at television by French engineer Henry Saint-Rene using a system of bent glass rods for guiding light images • In 1898, American David Smith applied for a patent on a bent glass rod device to be used as a surgical lamp • In 1920's, idea of using arrays of transparent rods for transmission of images for television and facsimiles respectively patented by Englishman John Logie Baird and American Clarence W. Hansell

31. History of optical communications systems (continued) • In 1930, German medical student Heinrich Lamm was first person to assemble a bundle of optical fibers to carry an image • Objective was to look inside inaccessible parts of the body (fiberscope) • Images were of poor quality • In 1954, Dutch scientist Abraham Van Heel and British scientist Harold. H. Hopkins separately wrote papers on imaging bundles • Van Heel had idea of cladding bare fiber with material of lower refractive index • In 1956, Narinder S. Kapany of Imperial College in London invented glass-coated glass rod, coined term fiber optics • Not suited for communications • Applications in fiberscopes

32. History of optical communications systems (continued) • 1960 – ruby lasers • In 1961, Elias Snitzer of American Optical published theoretical description of single mode fibers • Fiber with a core so small it could carry light with only one wave-guide mode • Worked for a fiberscopes • Light loss too high for communications (one decibel per meter) • 1962 – lasers operating on semiconductor chips • 1964 – C. K. Kao identifies that maximum loss of ~20 db/km needed for communications • Corresponds to 1% of energy left after 1 km • Existing glasses not transparent enough • Speculated that losses of 1000 db/km result of impurities in glass

33. History of optical communications systems (continued) • 1970 — Corning Glass researchers Robert Maurer, Donald Keck and Peter Schultz invent fiber optic wire or “Optical Waveguide Fibers” • Fused silica, which has high melting point, low refractive index • “65,000” times more capacity than copper wire • By 1972, losses down to 4 db/km • Today, ~0.2 db/km • 1973 — Navy installs fiber-optic telephone link on a ship • In 1975, US Government links computers in the NORAD headquarters at Cheyenne Mountain using fiber optics to reduce interference • In 1977, first optical telephone communication system installed • 1.5 miles long, under downtown Chicago • Each optical fiber carried the equivalent of 672 voice channels

34. History of optical communications systems (continued) • 1980 — first long distance fiber optic link (Boston-Richmond) • 1984 — First SONET networks • 1987 — fiber amplifiers invented by Dave Payne at U of Southampton, UK • 1988 — first transatlantic fiber optic link (AT&T) • 1990s — Bragg filters • 1997 — Wave division multiplexing (WDM) • 2000 — dense wave division multiplexing (DWDM) • 2001-2007– industry consolidation; absorbing new technology and glut of existing fiber

35. Thrusts of fiber optics technology • As distribution mechanism for light • To see in otherwise inaccessible places • For high-speed communications

36. Speed history • 1790 — 5 bits • 1977 — 44.7 Megabits • 1982 — 400 Megabits • 1986 — 1.7 Gigabits • 1993 — 10 Gigabits • 1996 — 1 Terabit • 2002 — 3 Terabits • Comparison: entire world’s telephone traffic ~ 5 Tb/sec • Maximum capability: estimated to be 100 Tb/sec per fiber

37. Optical network bandwidth is exploding OC-192, 320l

38. How widespread are optical networks? Source: Teleglobe

39. Fiber optic terminology • Lambda (l): a single wavelength of light • SONET: Synchronous Optical Network—a transport technology for reliably sending information over optical fiber • Photonic: having to do with devices using light (photons) instead of electronics; analogous to “electronic” • Decibel (db): a unit of power gain or loss, relative to a source. Calculated as 10 log10 (P/Pref). If reference is 1 mw, expression “dbm” is often used.

40. Types of optical networks • Present • Simplest: SONET + 1 wavelength of light (l) • SONET + 2 l • SONET + Dense wave division multiplexing (DWDM) (many l’s) • Future • IP over ATM over SONET + DWDM • IP over ATM over SONET, private line + DWDM • IP over other transport layer • All optical networks

41. World is changing with migration to data from voice • Data-driven network • Ingress/egress ~2000 km • 80% long-haul, 20% short haul • Traffic statistics unpredictable • Annual growth rate ~30% • Voice-driven network • Ingress/egress ~500 km • 80% short-haul, 20% long haul • Traffic statistics predictable • Annual growth rate ~7% Source: Qtera Networks/NGN99

42. General communications system background • Analog and digital signals • Information theory • Layered communications architectures

43. Digital and analog signals

44. Analog and digital transmission

45. Parts of a pulse

46. Information theory background • Sampling • Digitizing • Pulse code modulation • Multiplexing • Time • Frequency • Wave • Information content

47. Sampling Source: Cisco Systems

48. Digitizing (quantizing) Source: Cisco Systems

49. Effect of quantizing 4 bits/ sample 8 bits/ sample 3 bits/ sample 2 bits/ sample Source: U of Waterloo

50. Pulse Code Modulation (PCM) Prefiltering Sampling Quantizing Transmission or storage of string of numbers