SC518

The course focuses on light as a means of communication, i.e., on the generation, modulation, transmission and detection of (in most cases invisible) light for information exchange over long-haul, medium-haul or even chip-scale distances. This so-called photonics must interact with electronics, because the information to be transmitted by photons is provided electronically, and the information to be delivered by photons has to be re-converted to electronic signals. Especially the combination of photonics and digital signal processing electronics is of paramount importance for increasing the capacity, data rate, reach and reliability of optical long-haul and medium-haul transmission. In addition, modern technology and advanced nanofabrication make it possible to combine hundreds of photonic integrated circuits (PIC) on a single microchip. Packaged together with electronic microchips, complex opto-electronic networks become feasible with unprecedented compactness and performance.

The extraordinary information capacity provided by optical communication networks has led to the most significant technological evolution of the past decades – the global internet. Every email, every streaming video, every online order and every voice or video call is transmitted through optical fibres made of ultra low-loss glass. Data centres distributed around the globe respond to user demands, store an enormous amount of data and are interconnected with optical links. Even mobile communication relies on optical fibres, because the receiving and transmitting base stations are connected optically among each other and to the internet.

This course covers the basic elements of optical communication networks, namely transmitters containing semiconductor lasers and modulators, the transmission medium comprising glass fibres and optical amplifiers and receivers with semiconductor photodetectors including their associated optical and electrical circuitry. Capacity and sensitivity limitations define the networks’ application areas. Four degrees of freedom for an electromagnetic field are already used for simultaneous and independent information transmission: Time, frequency (wavelength), quadrature and polarization. The fifth dimension is parallelization by space division multiplexing (SDM), which will be the route to avoid a future network capacity crunch.

The learning objective of the course is a basic understanding of the following topics, starting with simple concepts and proceeding to more advanced ideas:

• Learn the types of terrestrial and free-space optical communication networks
• Identify the basic components of terrestrial fibre-bound communication links
• Appreciate the respective advantages of direct and coherent information transmission
• Recognize advanced technologies for encoding and modulation
• Realize the theoretical and practical limitations of information transfer
• Comprehend the sources of noise and their impact on the transmission capacity
• Grasp the setup of an advanced passive optical network, and of a multi-carrier coherent system
• Become aware how a “capacity crunch” could impact our day-to-day lives and how it could be avoided

Graduate students, faculty, researchers, patent attorneys and technical personnel working in academia, in industry or in government laboratories. To understand the benefits and the prospective evolution of optical communication networks, some knowledge provided by an undergraduate course in physics or electrical engineering would be useful. A background in waveguides and pn-junctions is helpful, but not required. Past attendees of the course will find substantial updates and new information, and they are encouraged to attend again.

Wolfgang Freude is a Professor at the Institute of Photonics and Quantum Electronics and a Distinguished Senior Fellow, both at Karlsruhe Institute of Technology (KIT), Germany. He received the Dipl.­Ing. (MSEE) and Dr.­Ing. (PhDEE) degrees in Electrical Engineering in 1969 and 1975 from the University of Karlsruhe. His research activities are in the areas of optical and wireless high-data rate transmission, high­density integrated-optics with a focus on silicon photonics, photonic crystals and semiconductor optical amplifiers.

He has authored and co-authored more than 330 publications, co­authored a book entitled “Optical Communications” (in German), and authored or co­authored seven book chapters. Wolfgang Freude is an Honorary Doctor of Kharkov National University of Radioelectronics, Kharkov, Ukraine, and a member of VDE/ITG, IEEE and Optica. Among other engagements, he chaired the CLEO Subcommittee S&I 07 “Micro- and Nano-Photonic Devices” in 2012 and 2013, was General Chair (Program Chair) for the Subcommittee “Photonic Networks and Devices” of the Optica Advanced Photonics Congress in 2022 (2021), and he serves as an editorial board member for the Springer Nature Journals “Light: Science & Applications” and “Scientific Reports”.