The Optical Networking and Communication
Conference & Exhibition

Los Angeles Convention Center,
Los Angeles, California, USA

Short Courses

SC357 - Circuits and Equalization Methods for Short Reach Optical Links

Monday, 21 March
13:30 - 17:30

Short Course Level: Advanced Beginner


Alexander Rylyakov; Coriant, USA

Short Course Description:

Short reach (or computercom interconnect) links are defined as communication links found inside a single (possibly large) computer, reaching distances of up to several 100’s of meters. They are typically used in an environment featuring high integration levels (many thousands and tens of thousands of links) and high total aggregated bandwidth requirements (100’s of Tb/s and more).  The key performance parameters for short links are power efficiency, density, bandwidth, and cost. Many existing system and circuit solutions found in long haul (telecom or datacom) links are often not applicable to a short reach situation as being too bulky, too expensive or dissipating too much power. At the same time, at short distances the optical I/O is always in a direct competition with purely electrical wireline solutions, further driving the need for high power efficiency at high total aggregated bandwidth. To stay competitive, both optical and wireline links use highly specialized front-end circuits and equalization methods.

The main focus of the course will be on circuits for VCSEL-based multi-mode and for Silicon Photonics single-mode optical short reach links in the context of highly parallel, high bandwidth applications. For completeness, circuit topologies and performance parameters will be compared to corresponding wireline transceiver solutions.

We will start with outlining the basics of channel properties and communication techniques. We will then review the most common front-end I/O circuit topologies used in both optical and electrical short reach interconnects and compare their overall efficiencies. Typical transmitter and receiver architectures for both electrical and optical links will be presented, with discussion of basic functionality and performance requirements for each of the building blocks.  We will outline the similarities as well as the differences between the key front-end components (e.g., VCSEL driver vs wireline driver vs Silicon Photonic modulator driver), and their effect on the overall link performance. We will compare SiGe bipolar and CMOS technologies in terms of performance, power dissipation, area and cost. The review will also include a brief discussion of the high-speed digital MUX/DEMUX (serializer/deserializer) circuits and the CDR (clock and data recovery) function. Full link power efficiency examples will be presented  for several optical and wireline links, together with a discussion of scaling trends.

Equalization is an absolute necessity for electrical links due to severe bandwidth limitations of wireline channels, but optical solutions can also greatly benefit from equalization, even at short reach. We will discuss the most commonly used equalization methods:

• continuous-time linear equalizer (CTLE, often used on both sides of the link)
• feed-forward equalizer (FFE, typically employed in the transmitter pre-emphasis)
• decision-feedback equalizer (DFE, commonly present in the receiver)

High-level descriptions of several topologies of FFE transmitters and DFE receivers will be presented, together with a discussion of tradeoffs involved when selecting one equalizer over another, or using both. We will conclude with discussion of several recently published results demonstrating the benefits of equalization for short reach optical links.

Short Course Benefits:

This course should enable you to:

  • Outline overall transceiver architectures of typical wireline and optical short reach  links

  • Explain functionality and performance requirements of all key front-end I/O building blocks

  • Evaluate and compare the efficiencies of wireline and optical short reach interconnects

  • Compare SiGe bipolar and CMOS circuits for short reach optical and electrical links

  • Understand and compare equalization techniques (CTLE, FFE, DFE)

  • Discuss benefits and tradeoffs of equalization

  • Make an educated choice between an optical and electrical solution for short reach interconnect

Short Course Audience:

This course is for anyone interested in learning the basic transmitter and receiver circuit architectures for both optical and electrical short reach interconnects. The course will help gain the insight into the main tradeoffs involved in choosing between the optical and electrical links, as well as the integrated circuit topologies and technologies used in the transceiver circuits. The overview of advanced equalization techniques will be also of interest to audience already familiar with the basics of short reach interconnect.

Instructor Biography:

Alexander Rylyakov received the M.S. degree in physics from Moscow Institute of Physics and Technology in 1989 and the Ph.D. degree in physics from State University of New York at Stony Brook in 1997, where he worked on the design and testing of superconductor integrated circuits based on Josephson junctions.  In 1999 he joined the IBM T.J. Watson Research Center as a research staff member, working on the design and testing of high-speed digital and mixed-signal communication circuits for optical and channel-limited wireline communications. Many of those circuits, implemented in various generations of CMOS and SiGe bipolar, are now used in IBM products and several of them have established performance records in their respective technologies. Dr. Rylyakov's current research interests are in the areas of digital phase-locked loops for communication and microprocessor clocking, high-speed low power transceivers and equalization for wireline and optical communication, and integrated circuits for silicon photonics. He has published over 80 papers and has 20 patents issued, 48 filed.

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