The Optical Networking and Communication
Conference & Exhibition

San Diego Convention Center,
San Diego, California, USA

SC357 - Circuits and Equalization Methods for Coherent and Direct Detection Optical Links

Monday, 04 March
08:30 - 12:30

Short Course Level:


Alexander Rylyakov; Elenion, USA

Short Course Description:

We will start with an overview and comparison of different types of optical links: intensity modulated direct detection vs coherent, short reach vs long reach, multi-mode fiber vs single mode, direct modulation vs external modulation. We will discuss the main components of the link data path: starting with the DSP (or SerDes), driver, transmitter, optical channel, receiver, TIA and going back to DSP. We will also compare optical links to common wireline transceiver architectures.

The main focus of the course will be on circuits on the critical electro-optical interface: drivers and TIAs. We will discuss and compare drivers for different modulators types (MZI, EAM, ring, etc) as well as drivers for direct modulation (VCSEL, DML).  We will compare drivers for intensity modulated links (NRZ, PAM4) to drivers for coherent communication (QPSK, 16QAM). We will discuss the main tradeoffs and ways to achieve the desired combination of bandwidth, linearity, power dissipation and output optical power. We will also discuss the main performance metrics of the TIAs: input referred noise, transimpedance gain, bandwidth and linearity in the context of different types of optical links. We will review and compare different driver and TIA circuit architectures on the transistor level. We will discuss the benefits of electro-optical co-design, when circuits and optical devices are optimized together to achieve the best possible overall performance of the link.

Equalization is an absolute necessity for electrical links due to severe bandwidth limitations of wireline channels, but optical solutions 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 also review the key building blocks and overall architectures of typical wireline SerDes/retimer and coherent DSP, and their impact on the electro-optical analog front end. Full link power efficiency examples will be presented for several optical and wireline links, together with a discussion of scaling trends.

Short Course Benefits:

This course should enable you to:

  • Outline overall transceiver architectures of optical and wireline links

  • Compare different types of optical links (e.g., coherent vs direct detection)

  • Understand the critical interface between analog circuits and optics

  • Analyze key performance metrics of drivers and TIAs

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

  • Discuss benefits and tradeoffs of equalization

  • Evaluate and compare power efficiencies of wireline and optical interconnects

Short Course Audience:

This course is for anyone interested in learning the transmitter and receiver circuit architectures for optical communications. The course will help gain the insight into the main tradeoffs involved in driver and TIA design and the impact on the overall performance of the link. 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 and the Ph.D. degree in physics from State University of New York at Stony Brook, where he worked on integrated circuits based on Josephson junctions.  From 1999 to 2014 he was with IBM T.J. Watson Research Center as a research staff member, working on high-speed mixed-signal communication circuits for optical and wireline communications and digital PLLs. In 2015 he joined Elenion Technologies working on integrated circuits for silicon photonics. He has published over 100 papers and has over 50 patents.

Sponsored by: