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

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

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) FeatureCWDMDWDM Wavelengths per fiber8 – 1640 – 80 Wavelength spacing2500GHz (20nm)100 GHz (0.8nm) Wavelength capacityUp to 2.5 GbpsUp to 10 Gbps Aggregate fiber capacity20 – 40 Gbps100 – 1000 Gbps Overall costLowMedium ApplicationsEnterprise, metro-accessAccess, metro-core, regional

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

13 Overview WDM Components Optical Multiplexer Optical De-multiplexer Optical Add/Drop Multiplexer (OADM) n

14 λ1λ1 λ2λ2 λ3λ3 λ4λ4 λ5λ5 λ6λ6 λ7λ7 λ8λ8 MultiplexerDemultiplexer λ1λ1 λ2λ2 λ3λ3 λ4λ4 λ5λ5 λ6λ6 λ7λ7 λ8λ8 Add/Drop Multiplexer λ 1 λ 2 λ 3 λ 4 λ 5 λ 6 λ 7 λ 8 Transmission Fiber WDM Block Diagram TransmittersReceivers

15 Components: Transmitters Each transmitter emits a signal at different wavelengths Laser source λ1λ1 λ2λ2 λ3λ3 λ4λ4 λ5λ5 λ6λ6 λ7λ7 λ8λ8

16 Components: Multiplexer 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 Multiplexer λ 1 λ 2 λ 3 λ 4 λ 5 λ 6 λ 7 λ 8

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 λ 1 +λ 2 λ1λ1 λ2λ2

19 Components: Add/Drop Multiplexer Signal at specific wavelength can be extracted Different signal at same wavelength can then be inserted Fiber Bragg Grating Add/Drop Multiplexer Transmission Fiber λ4λ4 λ 1 λ 2 λ 3 λ 4 λ 5 λ 6 λ 7 λ 8 λ 1 λ 2 λ 3 λ 4 ’ λ 5 λ 6 λ 7 λ 8 λ4’λ4’

20 Components: Demultiplexer Decouples different wavelengths to get different signals Demultiplexer λ 1 λ 2 λ 3 λ 4 λ 5 λ 6 λ 7 λ 8

21 Components: Receivers Optical detector Receives a specific signal at a specific wavelength λ1λ1 λ2λ2 λ3λ3 λ4λ4 λ5λ5 λ6λ6 λ7λ7 λ8λ8

22 Overview Sub-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.