Lecture 2. Introduction to Optical. Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2. Slide 1

Transcription

1 Lecture 2 Introduction to Optical Networks Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 1

2 Optical Communication Networks 1. Why optical? 2. How does it work? 3. How to design and analyze optical networks? k? 4. Existing network standards. Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 2

3 Communication: Why Optical Fiber? Hi! What? Data in Long distance Data out Transmitter Electrical Pulses / Electromagnetic Waves Receiver Physical limits for the bandwidth Wire ~ 1 MHz = 10 6 Hz Coaxial Cable ~ 10 GHz = Hz Microwave (wireless) ~ 100 GHz = Hz Optical Fiber ~ 100 THz = Hz Free Space Laser Beam ~ 1000 THz = Hz? The color of light is the limit Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 3

4 1995 Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 4

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9 Major components of an optical link Data in Data out Optical Transmitter Filter Receiver Amplifier Control Laser Fiber Photo Control Circuitsit Dt Detectort Circuitsit T1 R1 T1 Multiplexer R1 T2 Tn R2 Rn T2 Tn Demultiplexer R2 Rn Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 9

10 Light: Scales of Wavelength, Frequency, and Quantum Energy Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 10

11 Wavelength Standards Carrierfrequency: exact integer multiple of100ghz (maybe 50GHz or even 25GHz for a dense grid) c f λ = c = m/s λ[ nm] = f THz f = THz λ nm THz nm THz nm [ ] λ = 1.55 μm? f = THz λ nm THz nm 100 GHz f ITU Grid (International Telecommunication Union) Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 11

12 Typical spectral efficiency ~ 0.4 b/s/hz (with the simplest modulation format: amplitude shift keying, ASK) 10 Gb/s 10/0.4 = 25GHz frequency bandwidth required B 3dB = 25 GHz B 30dB >> 25 GHz f 0 f Δf = 100 GHz is chosen to accommodate easily up to 10 Gb/s data rate with simple ASK modulation format. Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 12

13 Wavelength bands O band ( Original ) nm * E band ( Extended ) nm S band ( Short wave ) nm C band ( Conventional ) nm * L band ( Long wave ) nm U band ( Ultra Long wave ) nm Reason for breaking the wavelength scale into bands: different types of sources, amplifiers, dt detectors t are used in different bands. Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 13

14 Sample problem How many 100 GHz ITU channels are covered by the C band 1530nm 1565nm? λ = 1530 nm f = THz λ = 1565 nm f = THz THz THz THz THz THz THz 195.9THz 191.6THz 0.1Thz + 1 = 44 Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 14

15 Networks Local area networks, LAN (typical distance ~ 1 km) Metropolitan area networks, MAN (~ 10 km) Wide area networks, WAN (~ 100 km) Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 15

16 Networks LAN: Provides communication access to users. Bit rate requirement is relatively low. Main issue is scalable and reconfigurable architecture to provide service for users. MAN: Provides communication access within a city. Moderate bit rate requirement. Fixed architecture is acceptable in many cases. WAN: Provides communication over long distance. High bit rate is required. Use of multiplexing techniques is necessary. The major issue is compensation for optical losses and dispersion. Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 16

17 First Generation Optical Networks Use existing topology of communication networks; replace copper cable links with optical fiber. All the signal routing and information processing is done electronically (not otoptically) Early stage (pre commercial): λ = 0.85 μm GaAs/AlGaAs lasers and multimode fibers. Reason for choosing the wavelength range: the only semiconductor lasers available at the time. Later (first commercial lines): λ = 1.3 μm InGaAsP lasers and singlemode fibers. Reason for choosing the wavelength range: zero dispersion in fused quartz fibers. Then: λ = 1.55 μm, singlemode fibers. Reason for choosing the wavelength range: minimal optical absorption in fused quartz fibers. Examples: SONET (Synchronous Optical Network), USA SDN (Synchronous Digital Hierarchy), International FDDI (Fiber Distributed Data Interface) Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 17

18 Multiplexing techniques Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 18

19 No speed limit associated with slow electronics. Delay lines are optical. Signal processing is all optical. Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 19

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21 Second generation optical networks Use optics for switching and routing Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 21

22 Communication services available with the second generation optical networks 1) Lightpath th Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 22

23 Communication services available with the second generation optical networks Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 23

24 Communication services available with the second generation optical networks Ivan Avrutsky, ECE 5870 Optical Communication Networks, Lecture 2 Slide 24