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Fiber Optic Communications Systems

Fiber Optic Communications Systems. Optical Time Division Multiplexing. From the movie Warriors of the Net. Multiplexing. Frequency-division multiplexing (FDM) for electrical signals Code-division multiplexing (CDM) for electrical signals

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Fiber Optic Communications Systems

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  1. Fiber Optic Communications Systems Optical Time Division Multiplexing From the movie Warriors of the Net

  2. Multiplexing • Frequency-division multiplexing (FDM) for electrical signals • Code-division multiplexing (CDM) for electrical signals • Wavelength-division multiplexing (WDM) for optical signals • Time-division multiplexing (TDM) for both types

  3. Modulation • Amplitude modulation • Frequency modulation • Phase modulation

  4. Simple to implement • amplitude modulation • pulse amplitude modulation • amplitude shift keying

  5. Economize bandwidth • quadrature amplitude modulation • single sideband modulation • vestigial sideband modulation

  6. Noise resistant • phase modulation • frequency modulation • pulse position modulation • pulse code modulation (widely used) • amplitude shift keying • frequency shift keying

  7. OTDM Bit Interleaved Multiplexer

  8. Wavelength Division Multiplexing (WDM)

  9. Overview • Wave Division Mutiplexing (WDM) multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. • Bit rate and protocol independent

  10. Overview

  11. Overview • Two main types of WDM: • Coarse Wavelength Division Multiplexing (CWDM) • Dense Wavelength Division Multiplexing (DWDM)

  12. Overview 1550 Window 1310 Window • Fiber Characteristics C Band Range : 1530nm – 1560nm L Band Range : 1570nm – 1600nm Water Peak

  13. OverviewWDM Components Optical Add/Drop Multiplexer (OADM) l1 l1...n l2 l3 Optical Multiplexer l1 l1 l1...n l2 l2 l3 l3 Optical De-multiplexer

  14. WDM Block Diagram Transmitters Receivers λ1 λ1 λ2 λ2 λ3 λ3 λ4 λ4 Multiplexer Demultiplexer λ5 λ5 Transmission Fiber λ6 λ6 λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8 λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8 Add/Drop Multiplexer λ7 λ7 λ8 λ8

  15. Each transmitter emits a signal at different wavelengths Laser source Components: Transmitters λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8

  16. All different signals from transmitters are combined into one signal The signal consists of several wavelengths, each containing a different signal Gratings, prisms and thin films Components: Multiplexer Multiplexer λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8

  17. Gratings • Simultaneously diffract all wavelengths • Simple device

  18. Classical Grating • Reflects light at an angle related to its wavelength • Diffraction angle is dependent on the groove spacing and incident angle Reflective Grating λ1 λ2 λ1+λ2

  19. Components: Add/Drop Multiplexer Add/Drop Multiplexer λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8 λ1 λ2 λ3 λ4’ λ5 λ6 λ7 λ8 Transmission Fiber λ4’ λ4 • Signal at specific wavelength can be extracted • Different signal at same wavelength can then be inserted • Fiber Bragg Grating

  20. Decouples different wavelengths to get different signals Components: Demultiplexer λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8 Demultiplexer

  21. Optical detector Receives a specific signal at a specific wavelength Components: Receivers λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8

  22. OverviewSub-Lambda Multiplexing • Multiplexing a single low rate data connection onto a wavelength is very inefficient. • For example, if a FastEthernet connection is transported on a WDM wavelength, only 4% of the bandwidth is used. This assumes the wavelength is capable of transporting 2.5 Gbps. • To better utilize bandwidth many vendors support sub-lambda multiplexing. • The cards that support this are often referred to as DataMux or Muxponder cards. • Muxponder cards have multiple ports (FE, GE, etc.). These cards multiplex the data flows and transports them onto a wavelength.

  23. Benefits of WDM • WDM technology allows multiple connections over one fiber thus reducing fiber plant requirement. • This is mainly beneficial for long-haul applications. • Campus applications require a cost benefit analysis. • WDM technology can also provide fiber redundancy. • WDM provides a managed fiber service.

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