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DWDM, CWDM, ROADM & COHERENT OPTICAL SYSTEMS: Fundamentals, Technology, Tests, Current Issues and Trends

Course Summary:

WDM technology (Wavelength Division Multiplexing) has revolutionized the telecommunications market in the whole world by offering a phenomenal cost-effective increase in the fiber transmission capacity. DWDM (Dense WDM) became commercial in 1995 while CWDM (Coarse WDM) emerged after 2000, stimulated by the telecom crisis. CWDM brings simpler technological concepts as compared to DWDM, cutting down prices, but fits just the lower transmission capacity markets, such as the metro and enterprise networks. More recently, two new paradigmatic revolutions have made their way into the optical communication market: ROADM (Reconfigurable Optical Add-Drop Multiplexing) and Coherent Optical Systems. While these optical technologies are the perfect solutions to satisfy the growing demand for bandwidth they also provide radical cost reduction in information transmission market.

Course Contents:

Review of optical communications:

  • Introduction
  • Evolution of optical communications
  • Some essential components
    • Optical fibers (types, attenuation and dispersion characteristics)
    • Optical splitters, combiners and couplers
    • Optical filters, multiplexers, demultiplexers
    • Transmitters and receivers
  • Usual multiplexing techniques in optical communications
    • TDM - Time-Division Multiplexing
    • WDM - Wavelength Division Multiplexing
  • SDH & SONET - Synchronous Digital Hierarchy
  • Other transmission protocols and respective data rates
Impairments in Optical Communications:
  • Optical attenuation
  • Chromatic dispersion
  • Polarization Mode Dispersion - PMD
  • Optical non-linearities
  • Optical signal to noise ratio (OSNR) and EDFA noise
  • Optical amplification
    • Fundamental characteristics
    • Basic configurations
    • Semiconductors amplifiers
    • Praseodymium doped fiber amplifiers (1.3mm)
    • Erbium doped fiber amplifiers (1.5mm)
    • Applications
  • Chromatic dispersion compensation in high capacity optical transmission systems
  • Challenges for implementing modern optical transmission technologies
WDM Technology:
  • DWDM and CWDM driving factors
  • Alternatives for increasing transmission capacity
  • Evolution of the WDM technology
  • Wide-Band WDM (WWDM), Coarse WDM (CWDM) and Dense WDM (DWDM)
  • DWDM - Technical, economical and logistic advantages
    • Bandwidth, scalability, transparency to bit-rate and modulation format, cost, investment risks, installation, future proof
  • Technologies that made DWDM technology possible
    • EDFA optical amplifiers
    • DFB Lasers with narrow and stable line widths
    • Fiber Bragg gratings
    • AWG - Arrayed Waveguide Grating
  • Main DWDM network components
    • Fixed and tunable transmitters
    • Optical receivers
    • Flat gain EDFA amplifiers
    • Wavelength multiplexers and demultiplexers
    • Fixed and configurable optical Add-Drop multiplexers
    • Optical Cross-Connects
  • Bidirectional DWDM
  • Considerations about channel separation and channel selection
    • Channel selection and cross-talk
    • Channel spacing and channel count
    • Differences between DWDM and CWDM channel spacing
    • ITU standardization and frequency grid
  • Chromatic dispersion management and dispersion compensation in WDM systems
  • WDM impairments due to optical non-linearities
    • Raman Scattering and Brillouin Scattering
    • Self phase modulation and cross phase modulation
    • Four-wave mixing
  • CWDM - Characteristics, standardization and applications
  • CWDM - Technical, economical and logistic advantages
  • Comparisons between DWDM and CWDM
  • Network investments - important evaluations in the decision making process
  • New optical fibers for DWDM and CWDM - Which to choose?
    • Dispersion characteristics, effective area, second order dispersion
    • Advantages and disadvantages in DWDM and CWDM
  • TDM versus CWDM & DWDM, STM-16 versus STM-64 and STM-256*
    • Which and/or when each alternative is better
  • Open architecture versus closed architecture in DWDM
  • Protection, restoration and reliability in the optical layer
  • CWDM & DWDM solutions available in the market
  • Interoperability between suppliers
  • Network design methodology
  • Case studies
Recent technology revolutions in the optical communication market:
  • Photonic networks and all optical networking
  • Optical layer, optical routing and elements of all-optical networking
  • ROADM - Reconfigurable Optical Add-Drop Multiplexing
  • Coherent optical communications
  • New optical modulation schemes for 40 – 100Gb/s transmission
  • DP-QPSK
  • Use of Digital Signal Processing along with coherent optical systems to alleviate chromatic dispersion, polarization mode dispersion and OSNR impairments
Tests and Measures in WDM Networks:
  • Spectral measurements in WDM
  • Essential characteristics of the OSA
  • Technologies of spectral analysis
    • The Optical Spectrum Analyzer (OSA)
    • Wavelength Meter
    • Tunable filter based equipments
  • Required tests and measurement parameters
    • Components
    • System performance
    • Field installation and maintenance
  • Use of OSA in the installation, monitoring and fault repairing of WDM networks
  • WDM test equipment suppliers
  • Specialized diagnostics of optical networks
  • PMD audits in the American, Swedish and Brazilian fiber plants
Current issues in WDM optical networking:
  • Networks centered in voice services versus networks centered in data services
  • IP and ATM over WDM
  • The optical internet and MPLS
  • DWDM and CWDM in Metropolitan Area Networks (MAN's)
  • The LAN invades the WAN and WAN invades the LAN
  • L-band EDFA optical amplifier (1570-1620nm)
  • Ultra-wide band EDFA optical amplifier (1530-1620nm)
  • Raman optical amplifiers
  • DWDM in dispersion shifted (DS) fibers
  • Dispersion compensation in DWDM systems using fiber Bragg gratings (FBG)
  • Optical TDM - OTDM
  • Link PMD
  • PMD compensation
  • Forward Error Correction - FEC
  • DWDM in CATV networks
  • FSO (Free Space Optical) communication systems - the optical wireless success
CWDM & DWDM Market:
  • DWDM & CWDM market driving factors
  • Market euphoria, crisis and recovering
  • Historic evolution of the worldwide WDM market

Duration: 24 Hours

Instructor: Sergio Barcelos, PhD

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