ENE623/EIE 696 Optical Networks

1. ENE623/EIE 696 Optical Networks Lecture 1

2. Historical Development of Optical Communications • 1790 – Claude Chappe invented ‘optical telegraph’. • 1880 – Graham Bell invented ‘photophone’. • 1930 – Heinrich Lamm presented unclad-fibers, but it showed poor performance. • 1954 – van Heel and Kapany reported about the 1st clad-fibers by covering a bare fiber with a transparent of lower refractive index.

3. Historical Development of Optical Communications • 1960 – Maimen demonstrated the 1st laser for communications. • 1966 – Kuo and Hockham introduced fiber communications with low attenuation (< 20 dB/km). • 1970 – Maurer, Keck, and Schultz made a single-mode fused silica fiber (very pure with high melting point and a low refractive index) for 633 nm wavelength of HeNe laser. • 1977 – Fibers used at 850 nm from GaAlAs laser.

4. Historical Development of Optical Communications • 1980’s – A 2nd generation of optical communication at 1300 nm with 0.5 dB/km for fiber attenuation. • 1990’s – A 3rd generation operates at 1550 nm with fiber loss of 0.2 dB/km with EDFA serving as an optical amplifier . Signals also could be sent via WDM.

5. Preview on Fiber Optic Communication • Basic schematic diagram

6. Preview on Fiber Optic Communication • The advantages of optical fiber communication over electrical based system are • Low attenuation • High bandwidth • Immune to electro-magnetic interference • Short circuiting, Earthing, and Fire Free • Low in weight and volume • Data security

7. Preview on Fiber Optic Communication • The transmission passbands for installed fibers today are 0.85, 1.3, and 1.55 μm (near-infrared). • Wavelength of 1.6+ μm can be seen in some applications. • There are more than 25,000 GHz of capacity in each of the three wavelength bands.

8. Preview on Fiber Optic Communication • Digitaltransmission – The sampling theorem says that an analog signal can be accurately transmitted if sampling rate is twice the highest frequency contained in that signal. • Let R be the required transmission rate. R can be expressed by where m = number of bits/sample fs= sampling frequency = 2(f)

9. Preview on Fiber Optic Communication

10. Preview on Fiber Optic Communication

11. Example 1 • A telephone system has m = 8 bits/sample. Find R. • Soln

12. Preview on Fiber Optic Communication • A transmission standard developed for optical communication is called SONET (Synchronous Optical NETwork).

13. Preview on Fiber Optic Communication

14. Installations • Optical fiber installations: • on poles • in ducts • undersea

15. Fiber Attenuation History

16. Preview on Fiber Optic Networks • Fiber-To-The-Home (FTTH) 2.5 Gbps Mid 90’s 10 Gbps  y2k 40 Gbps and beyond  state of art

17. Preview on Fiber Optic Networks • Now a number of channels per fiber is more than 128. • This was increased from 32 channels/fiber in 2004. • The link attenuation is less than 0.2 dB/km at 1.55 μm wavelength. • BER can be achieved at 10-15 with a help of Er-doped fiber amplifier (EDFA).

18. Optical Fiber Source: ARC Electronics http://www.arcelect.com/fibercable.htm

19. Fibers Source: Optical Fiber Communications, G.Keiser, McGraw Hill.

20. Connectors Source: ARC Electronics http://www.arcelect.com/fibercable.htm

21. Optical communication systems • Multiplexing refers to transmission of multiple channels over one fiber. • Channels can be data, voice, video, and so on. • We may classify the communication systems into 3 classes as: • Point-to-point link • Multipoint link • Network

22. Example 2 • A cable consists of 100 fibers. Each fiber can carry signals of 5 Gbps. If audio message encoded with 8 bits/sample is being sent, how many conversations can be sent via one cable? • Soln

23. Example 3 • By using the same cable as previous example, how many TV channels could be sent via a cable. • Soln

24. Generations of Fiber Usage • Bandwidth and error rate improved (fatter links), but propagation delay not changed (same length). Source: Fiber Optic Network Paul E. Green, Prentice Hall.

25. Generations of Fiber Usage • First generation: no fiber (copper link) • 2nd generation: • Fiber used for point-to-point link only. • Multiplexing & switching carried out electronically. • 3rd generation: • Fiber used for multiplexing and switching as well as point-to-point transmission.

26. Generations of Fiber Usage • Copper links • Copper links are more vulnerable to outside influence since moving electrons influence each other. • It is also affected by electromagnetic wave (EM wave). • Fiber links • Moving photons of light in a fiber do not interact with other moving photons. • EM wave has no effect on a fiber as well.

27. Fiber Bandwidth • We all know that • where λ= free-space wavelength ν = optical frequency c = speed of light at free-space

28. Fiber Bandwidth • At  = 1.5 µm, the attenuation is about 0.2 dB/km, and there is a window about  = 200 nm wide between wavelengths having double that number of dB per kilometer. • The useful bandwidth is about 25,000 GHz.

29. Fiber Bandwidth • This can applied to  = 1.3 µm and 0.85 µm as well. • For 0.85 µm, this band is not defined by an attenuation standpoint, but by the range which GaAs components can be easily made.

30. Fiber Bandwidth

31. Multiplexing • Space Division Multiplexing • Frequency Division Multiplexing • Time Division Multiplexing • Wavelength Division Multiplexing

32. Wavelength-Division Multiplexing • For example, 16 channel WDM using 1,300 nm or 1,550 nm with 100 GHz channel spacing. • Therefore, bandwidth = 16 x 100 = 1,600 GHz. • LAN = Local Area Network (< 2 km) • MAN = Metropolitan Area Network ( < 100 km) • WAN = Wide Area Network (unlimited)