The student will acquire the knowledge of: • the reasons why optical fiber systems are today the backbone of fixed telecommunication networks • optical fiber transmission systems main features, performance, potential and impairments • the related transmitter and receiver technologies and algorithms needed to achieve reliable communication over fiber The expected outcome of the course is the ability for the student to: • understand the design and optimization process of practical optical transmitter and receiver systems, as well as of the fiber plant connecting them • apply such design techniques and optimization processes autonomously to practical transmission system examples.

This course has the following mandatory prerequisites • a thorough understanding of the mathematical topics presented in Engineering Bachelor (or "Laurea") degree, including calculus and linear algebra. • bachelor-level prior knowledge on the fundamentals of electromagnetism, and in particular on field propagation in guided systems • a sound and well-established prior knowledge of the fundamentals of signal theory (including probability and stochastic processes) and of basic digital communications (digital modulations and their performance on the AWGN channel).

These are the main topics of the course: • Introduction to optical communication systems (3 hours) • System level description of the key optoelectronic components for optical fiber communications (6 hours) • semiconductor lasers • external modulators • optical filters • optical amplifiers • optoelectronic receivers based on photodiodes • Linear and non-linear propagation effects in single-mode optical fibers (6 hours) • chromatic dispersion • polarization linear effects • the Kerr non-linear effect • modeling of the interaction of linear and non-linear effects • Direct-detection systems based on PAM-M without optical amplification (12 hours) • practical non-amplified systems: typical structure, PIN+TIA or APD photodetection, modeling and performance calculation • design of systems using non-amplified systems: short and medium-haul systems, access and last-mile fiber-to-the-home (FTTH) systems based on PAM-M transmission • the ideal on-off optical transmission systems: an introduction to quantum-limited optical systems • Coherent transmission systems based on PM-QAM and optical amplification • generalities and description, block diagrams (3 hours) • ideal performance characterization in ASE noise (3 hours) • receiver DSP block diagrams and algorithms (6 hours) • coherent transmission systems and fiber nonlinearities: the Gaussian Noise model (8 hours) • Raman amplification and further fiber propagation effects (6 hours) • Seminars on application scenarios and related design optimization: (7 hours) • data-center networks • access networks (fiber-to-the-home, or FTTH) • multi-thousand km submarine systems • optically-routed national and international backbone networks • a look towards the future: quantum cryptography Note: each year two or three seminars out of the ones indicated above will be offered.

Theoretical lectures will be complemented by practice classes, which will be devoted to the solution of numerical problems and of small design projects on the course main topics, which are always related to real optical transmission systems with realistic parameters. These exercises will be solved in class. A laboratory experience will be conducted at the PhotoNext experimental laboratory. The break-up among theoretical lectures, practice classes and laboratory experience is: theoretical lectures: 36 hours practice classes: 20 hours laboratory experience: 4 hours (all figures approximately). For the students enrolled in the Electronic Engineering degree: a 12-hour tutorial on digital communication theory will be proposed in class. During the course, homework assignment may be carried out and evaluated. Specifically: - Homework may be assigned on IM-DD transmission systems - Homework may be assigned on coherent transmission systems In addition, a mandatory report on the experience conducted at the PhotoNext experimental laboratory is requested.

The optical system topics are fully covered by the material (handouts) provided by the teachers, both for the lectures and the design problems. All such material will be available on the website prior to classes. No specific extra material is needed. For personal further reading on optical fiber systems: • Springer Handbook of Optical Networks. Editors: Mukherjee, Tomkos, Tornatore, Winzer, Zhao. Springer Nature Switzerland, 2020. • Optical Fiber Telecommunications Volume VIA and VIB: Systems and Networks (Optics and Photonics) by Kaminow, Ivan, Li, Tingye and Willner, Alan E., Academic Press; 6 edition (May 11, 2013). ASIN: B00CZANHGW • Xiang Zhou and Chongjin Xie, Enabling Technologies for High Spectral-efficiency Coherent Optical Communication Networks, John Wiley and Sons, Inc., 2015. • J.Proakis and M.Salehi, Digital Communications (5th ed). McGraw-Hill, 2008.

Lecture slides; Exercises; Exercise with solutions ; Video lectures (previous years);

Exam: Written test; Optional oral exam;

The written exam is based on: - two numerical system design exercises, similar to those that will be solved during the course. - two-three theoretical questions, requiring a free-text answer. The goal of the exam is to verify that the students understand the design and optimization process of practical optical transmitter and receiver systems, as well as of the fiber plant connecting them, and that they can apply such design techniques and optimization processes autonomously to practical transmission system examples. The exam will last two hours and it will be scored on a full scale up to 30. The evaluation of the written exam is based on the correct development of the proposed exercises from the description of the symbolic-formula solutions up to the numerical results. The theoretical questions will be judged according to the completeness of the answers, but also on the ability of the students to reply in a concise way. The written exam proposes exercises that allows to judge if the student knows the topic of the course and is able to apply this knowledge to solve some simplified design examples on modern digital transmission systems. The open questions allows to judge if the student has acquired the most relevant theoretical topic of the course. This written exam is a “closed-book exam”. During the written exam the student can use only: • A pocket calculator (NO laptop, tablets etc. Any type of cellphone should be switched OFF) • A 4 pages (max) summary of formulas written by the student herself/himself (4 pages total, meaning 2 sheets if one writes on the front and back of each sheet) • No other technical material is allowed (thus no books, handouts, old exercises, etc) The students who will get a score above 15/30 at the written exam can ask for an optional oral exam, where the questions will mostly regard the theoretical aspects of the course. The optional oral exam is always organized a few days after the written exams. It awards between -5 and +5 points, that are added to the result of the written exam. During the semester, the Teachers will moreover propose three activities/homework, that the students solve and send to the Teachers. They will be evaluated and a maximum score of 2 points will be awarded to each of the 3 activities, for a total maximum of 6 points. The final grade for Optical Communication is the sum of the aforementioned results of the written exam + activities/homework + optional oral exam. If this final sum is above 32, the student will get “30 cum laude”.

In addition to the message sent by the online system, students with disabilities or Specific Learning Disorders (SLD) are invited to directly inform the professor in charge of the course about the special arrangements for the exam that have been agreed with the Special Needs Unit. The professor has to be informed at least one week before the beginning of the examination session in order to provide students with the most suitable arrangements for each specific type of exam.