Communications II

Optical communication systems are the backbone of today's wordwide communication infrastructure. Fiber optical links connect data centers, cities and continents; free-space optical links connect satellites and space vehicles with earth-bound basestations. This lecture introduces physical layer technologies and modulation as well as detection schemes to communicate across different optical media.

1 Overview
1.1 Evolution of Data Capacity Requirements
1.2 Metallic Waveguides as Competitor
1.3 Optical Access and Transport Network
1.4 Optical Submarine Cables
1.5 Free-Space Optical Communications
1.6 This Optical Communications Course
1.6.1 Typical Operations of Transmitters
1.6.2 Typical Aspects of the Communication Channel
1.6.3 Typical Operations in a Receiver
1.7 Technical Milestones and Future Trends
1.7.1 Important Milestones of the past 30 Years
1.7.2 Trends and Future Developments

2 Optical Communication Channel
2.1 Frequency band of optical communications
2.2 Basics of Geometrical Optics
2.3 Basics of Optical Fibers
2.4 Step-index Fiber
2.5 Modal Dispersion
2.6 Graded-index Fiber
2.7 Single Mode Fiber
2.7.1 Wave Propagation Equation
2.8 Chromatische Dispersion
2.8.1 Propagation Delays by Chromatic Dispersion
2.8.2 Definition of the Dispersion Coefficient and its Slope
2.8.3 Pulse Widening through Chromatic Dispersion
2.9 Non-linear Schroedinger Equation (NLSE)
2.9.1 Transfer function of the fiber (chromatic dispersion only)
2.9.2 Attenuation
2.10 Optical amplifiers
2.10.1 Erbium-doped fiber amplifier, EDFA
2.10.2 Considering one Amplifier
2.10.3 Considering an Amplifier Cascade
2.10.4 Raman-amplification
2.11 Power and dispersion budget
2.12 Further (non-)linear impairments and noise
2.13 Soliton Propagation
2.13.1 Special properties of soliton impulses
2.13.2 Simulation by Split-Step-Fourier Method (SSFM)
2.13.3 Non-ideal soliton pulse shaping
2.13.4 Higher-order solitons
2.14 Free-Space Optical Channel
2.14.1 Transmit Laser Beam-Shapes
2.14.2 Modeling Atmospheric Turbulence and Scintillation
2.14.3 Simulation using the Split-Step Fourier Method
2.14.4 Some real-world examples
2.14.5 Comparison to RF

3 Optical Intensity-based Communication
3.1 Direct modulation
3.2 External modulation with Mach-Zehnder Modulator
3.2.1 Block diagram
3.2.2 Splitter/coupler
3.2.3 Transfer characteristic
3.2.4 Modes of operation
3.3 Pulse Shaping
3.3.1 Non-Return-to-Zero (NRZ), Return-to-Zero (RZ)
3.4 Eye diagram

4 Differential Communication
4.1 DPSK (one bit per symbol)
4.2 DQPSK (two bits per symbol)

5 Optical Coherent Communication
5.1 Modulation
5.1.1 Mach-Zehnder arrangements for coherent communication
5.2 Demodulation
5.2.1 Coherent detection by superposition
5.2.2 2x4 90-degree hybrid
5.2.3 Constellation diagram after chromatic dispersion
5.2.4 Polarization multiplex
5.2.5 Frequency offset estimation and compensation
5.2.6 Dispersion compensation by digital equalization

A Appendix
A.1 Wavelength Dependency of Refractive Index, Sellmeier-Equation
A.2 Computing the Material Dispersion from the Wavelength Dependency
of the Refractive Index
A.3 Definition of the Optical Signal-to-Noise Ratio, OSNR
A.4 Properties of Optical Sources
A.4.1 LED
A.4.2 Laser-Diode, LD
A.5 Properties Optical Receivers
A.5.1 PIN-Photodiode
A.5.2 APD-Photodiode
A.6 Duobinary Modulation

Note: Course contents subject to change in order to keep up-to-date with latest research results and developments in the communications industry.