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Enhance your understanding of the failure mechanisms of optical components, and draft fault detection guidelines to design a robust Dense Wavelength Digital Multiplexing (DWDM) system and network that exhibits and maintains optical signal quality and system reliability.
This valuable reference builds on Dr. Kartalopoulos' seminal book on the subject, Introduction to DWDM Technology: Data in a Rainbow, providing an analytical approach to degradations and 'photonic' faults that affect the quality of the multiwavelength transmission of optical signals.
Organized in six chapters, FAULT DETECTABILITY IN DWDM includes detailed descriptions of the properties of light and optical communications, optical components, interaction of wavelengths and faults affecting the quality of the optical signal and the system, correlation of faults, aspects of fault management, and current issues in DWDM.
This comprehensive book directs practicing electrical engineers, optical systems designers, optical network architects, fault management engineers, technical managers, optical systems technical marketing and optical communications students on how to use DWDM technology efficiently, effectively and reliably.
Organized in six chapters, Fault Detectability in DWDM includes detailed descriptions of the properties of light and optical communications, optical components, interaction of wavelengths and faults affecting the quality of the optical signal and the system, correlation of faults, aspects of fault management, and current issues in DWDM.
The signal integrity in DWDM systems becomes increasingly complex as DWDM evolves, having more optical channels, higher bit rates, and increasing fiber spans. Unfortunately, the signal quality in the optical domain is very difficult to monitor, and one resorts to monitoring the quality of the signal after it has been converted to an electrical signal. Once this is done, standard methodology and techniques are used to measure the quality of the signal, such as eye diagrams (including threshold levels, triggering points, and amplitude levels) and BER measurements. However, one has to keep in mind that the quality of the electrical signal is not an exact representation of the quality of the optical signal. The former consists of degradations due to photonic interactions and optics that are superimposed with degradations due to optoelectronic conversion (quantum efficiency, diode noise, and temperature) and due to electronic components [capacitors, resistors, temperature, board-layout cross-talk (ground loops), connector cross-talk, sampling clock stability, and electromagnetic interference]. Many of these degradations add to the noise content of the signal, rise- and fall-time distortions, spikes, signal ripple, ground floor noise, temporal shifts, and waveform skew.
The content of errored bits in a signal is a key parameter that must be continuously monitored. We cannot lose sight of the fact that the responsibility of communications systems and networks is to transport in a timely manner to the receiving terminal (the sink end user) the same bits that the transmitting end terminal (the source end user) has sent. To safeguard this, standards define performance parameters pertaining to the frequency of bit errors, such as error seconds (ESs), severe error seconds (SESs), and severely errored period intensity (SEPI), as well as how to measure and report these performance parameters (a task beyond the scope of this book).
In the previous chapter we identified and classified the various parameters that when degrade and/or fail affect the quality of the optical signal. The objective of this chapter is to examine the degradation and failure mechanisms of optical components, which affect the optical signal quality, and their detectability. It examines the observable optical parameters and the predictors that infer (with a high degree of probability/possibility) degradation or failure and the remedial actions to be taken. It adds to the fault management design process in systems and in networks.
B. We identify types of faults of optical components and hint on the action to be triggered. For example, a component may fail (e.g., no laser optical power is de-tected), it is detected, and a unit replacement action (or switch to protection) may be invoked. As another example, a component may be degraded (e.g., laser optical power drops or center wavelength drifts) to a level that may result in increased BER (bit error rate) and/or ISI (intersymbol interference). In this case, a unit replacement action (or switch to protection) may proactively be invoked.
C. We correlate faults to infer conditions that may not be directly observable. Certain degradation and failures are directly and conclusively detected (e.g., laser output power loss), whereas certain others are indirectly detected by fault correlation (e.g., is BER increased due to FWM contribution or due to pulse spreading and increased ASE or to some other photonic error source?).
Correlation and inference may invoke actions to locate a hidden fault and to isolate it within a node. As an example, the malfunction of one or more of the mirrors in MEMS may result either in output power loss of a corresponding channel and/or in excess BER and cross-talk of another channel. Similarly, center wavelength drifts may cause BER and cross-talk in one or more channels or received power degradation if a selective filter or an optical add-drop multiplexer is involved.
The information provided about these components is formatted, as applicable, as follows:
Chapter 1: Properties of Light and Matter.
1.2: Nature of Light.
1.3: Reflection, Refraction, and Diffraction.
1.4: Polarization of Light.
1.5: Propagation of Light.
1.6: Fiber Birefringence and Polarization.
1.8: Fiber Attenuation and Loss.
1.9: Fiber Spectrum Utilization.
1.10: Nonlinear Phenomena.
1.11: Spectral Broadening.
1.12: Self-Phase Modulation.
1.13: Self-Modulation or Modulation Instability.
1.14: Effects of Temperature on Matter and Light.
1.15: Light Attributes.
1.16: Material Attributes.
1.17: Measurable Parameters.
Chapter 2: Optical Components.
2.2: Laser Sources.
2.3: Optical Comb Generators.
2.4: Chirped-Pulse Laser Sources.
2.7: Fixed Optical Filters.
2.8: Tunable Optical Filters.
2.9: Diffraction Gratings.
2.10: Arrayed Waveguide Grating.
2.11: Directional Couplers.
2.12: Optical Isolators.
2.13: Polarizers, Rotators, and Circulators.
2.14: Optical Equalizers.
2.16: Optical Multiplexers and Demultiplexers.
2.17: Optical Cross-Connects.
2.18: Optical Add-Drop Multiplexers.
2.19: Optical Amplifiers.
2.20: Classification of Optical Fiber Amplifiers.
2.21: Wavelength Converters.
Chapter 3: Parameters Affecting the Optical DWDM Signal.
3.2: Component Parameters.
Chapter 4: Faults Affecting the Optical DWDM Signal.
4.3: Filters: Fabry-Perot (Passive, Fixed).
4.4: Filters: Fiber Bragg Grating (Passive, Fixed).
4.5: Filters: Chirped FBG (Passive, Fixed).
4.6: Filters: Acousto-Optic Tunable Ti:LiNbO3.
4.7: SOA: InGaAsP.
4.8: OFA: Factors Affecting Integrity and Quality of Signal.
4.9: OFA: Single Pump.
4.10: OFA: Double Pump.
4.12: OXC: MEMS.
4.13: OXC: LiNbO3.
4.14: OXC Liquid Crystal.
4.15: OADM: LiNbO3 Based.
4.16: OADM: MEMS with Grating.
4.17: Transmitter: Laser.
4.18: Receiver: PIN Diode.
4.19: Fiber: Single Mode.
Chapter 5: Fault Correlation.
5.2: Correlation of Faults and Component Parameter Changes.
5.3: Open Issues: Nonlinear Effects.
Chapter 6: Toward DWDM Fault Management and Current Issues.
6.2: Toward Fault Management.
6.3: Current Issues.
6.4: Engineering DWDM Systems: Conclusion.
About the Author.