From Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH): “Ultrafast optical switching can save overwhelmed datacenters”

From Swiss Federal Institute of Technology in Lausanne [EPFL-École Polytechnique Fédérale de Lausanne] (CH)

Arslan Sajid Raja
Nik Papageorgiou

EPFL and Microsoft Research scientists demonstrated ultrafast optical circuit switching using a chip-based soliton comb laser and a completely passive diffraction grating device. This particular architecture could enable an energy-efficient optical datacenter to meet enormous data bandwidth requirements in future.

Services from all hyper-scale cloud providers like Microsoft are powered by massive datacenters that employ hundreds of thousands of servers, whose performance depends heavily on the quality of the network between them. Current datacenter networks include multiple layers of electrical packet switches interconnected through optical fibers. These systems require electrical-to-optical conversion, which increases cost and power overhead. To make things worse, growing data rates due to applications like AI and data analytics could concur with the slowdown of Moore’s law which would make it extremely difficult to efficiently scale current network architectures relying on electrical chips.

Optical circuit switches (OCS) are emerging as an exciting option for overcoming bandwidth and scaling issues at datacenters. A particularly promising OCS architecture is wavelength switching where different servers are connected using different colors (wavelengths) of light leading to flatter network architecture and limiting the need for electrical switches and optical transceivers. Switching different wavelengths of light and routing signals to destination servers is done by a switching element, e.g. a glass prism through which different wavelengths can be separated by dispersion.

Although OCS technologies are commercially available today, they are extremely slow, which means they cannot handle increasingly bursty datacenter applications while properly utilizing network resources to reduce overheads and improve power consumption.

In a new paper published in Nature Communications, research teams led by Professor Tobias J. Kippenberg at EPFL and by Dr Hitesh Ballani at Microsoft Research Cambridge have successfully demonstrated ultrafast OCS for datacenters by using chip-based optics. The research teams have collaborated since 2018 as part of the Microsoft Swiss Joint Research Center.

In the proposed architecture, optical microcombs act as a multiwavelength source providing coherent carriers. Optical amplifiers and arrayed waveguide gratings based on semiconductor materials perform the switching and separate or combine the different colors of light respectively.

Optical microcombs, pioneered by Kippenberg’s group, provide hundreds of equidistantly spaced carriers that are suitable for many applications. The microcomb sources are generated through nonlinear frequency-conversion by using a chip-scale silicon nitride microresonator, presenting unique advantages in power and size over the laser arrays conventionally used as multi-wavelength sources.

Silicon nitride microresonators are fabricated using the photonic damascene process, a CMOS-compatible technique that features ultra-low propagation loss, which is extremely critical to make power-efficient microcomb sources.

The chip-scale indium phosphide-based optical amplifiers, fabricated using commercial foundries, perform the switching between different colors of light at sub-nanosecond timescales. This ultra-fast switching between different microcomb carriers is important for meeting the performance requirements of modern and future datacenter applications.

A proof-of-concept, system-level demonstration showed that data transmission with packet-by-packet switching can be achieved and hence, has the potential to meet the requirements of datacenter applications. Finally, the researchers present a unique architecture that employs a central comb system to improve power efficiency and reduce complexity.

“Soliton microcombs have been used in many key system-level applications such as LiDAR, long-haul data transmission, and optical coherence tomography since their discovery back in 2014,” says Kippenberg. “The potential use of microcombs in datacenters to meet future bandwidth requirements and reduce power consumption further consolidate the importance of this platform for scientific and technological applications.”

“We have been intrigued by the tremendous potential of optical microcombs so it was fantastic to be able to collaborate with the EPFL team on the application of their world-leading silicon nitride microcomb technology to potentially future-proof our data center networks,” says Ballani. “While there is a long way to go to be able to operate our architecture at scale, the rapidly improving performance of microcombs and other on-chip optical devices means that the performance gains could be even higher”. Paolo Costa, a co-author from Microsoft Research added that “this collaboration is a very good example of how we are re-imagining the future of our networks, from the ground-up, by both developing and leveraging bleeding-edge optical technologies with our academic partners.”

The silicon nitride samples were fabricated and grown in the Center of MicroNanoTechnology (CMi) at EPFL.


Microsoft Swiss Joint Research Center (Joint research ICES)

Air Force Office of Scientific Research (AFOSR)

Swiss National Science Foundation (SNF)

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The Swiss Federal Institute of Technology in Lausanne [EPFL-École polytechnique fédérale de Lausanne] (CH) is a research institute and university in Lausanne, Switzerland, that specializes in natural sciences and engineering. It is one of the two Swiss Federal Institutes of Technology, and it has three main missions: education, research and technology transfer.

The QS World University Rankings ranks EPFL(CH) 14th in the world across all fields in their 2020/2021 ranking, whereas Times Higher Education World University Rankings ranks EPFL(CH) as the world’s 19th best school for Engineering and Technology in 2020.

EPFL(CH) is located in the French-speaking part of Switzerland; the sister institution in the German-speaking part of Switzerland is The Swiss Federal Institute of Technology ETH Zürich [Eidgenössische Technische Hochschule Zürich)](CH) . Associated with several specialized research institutes, the two universities form the Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles polytechniques fédérales] (CH) which is directly dependent on the Federal Department of Economic Affairs, Education and Research. In connection with research and teaching activities, EPFL(CH) operates a nuclear reactor CROCUS; a Tokamak Fusion reactor; a Blue Gene/Q Supercomputer; and P3 bio-hazard facilities.

ETH Zürich, EPFL (Swiss Federal Institute of Technology in Lausanne) [École polytechnique fédérale de Lausanne](CH), and four associated research institutes form the Domain of the Swiss Federal Institutes of Technology (ETH Domain) [ETH-Bereich; Domaine des Écoles polytechniques fédérales] (CH) with the aim of collaborating on scientific projects.

The roots of modern-day EPFL(CH) can be traced back to the foundation of a private school under the name École spéciale de Lausanne in 1853 at the initiative of Lois Rivier, a graduate of the École Centrale Paris (FR) and John Gay the then professor and rector of the Académie de Lausanne. At its inception it had only 11 students and the offices was located at Rue du Valentin in Lausanne. In 1869, it became the technical department of the public Académie de Lausanne. When the Académie was reorganised and acquired the status of a university in 1890, the technical faculty changed its name to École d’ingénieurs de l’Université de Lausanne. In 1946, it was renamed the École polytechnique de l’Université de Lausanne (EPUL). In 1969, the EPUL was separated from the rest of the University of Lausanne and became a federal institute under its current name. EPFL(CH), like ETH Zürich(CH), is thus directly controlled by the Swiss federal government. In contrast, all other universities in Switzerland are controlled by their respective cantonal governments. Following the nomination of Patrick Aebischer as president in 2000, EPFL(CH) has started to develop into the field of life sciences. It absorbed the Swiss Institute for Experimental Cancer Research (ISREC) in 2008.

In 1946, there were 360 students. In 1969, EPFL(CH) had 1,400 students and 55 professors. In the past two decades the university has grown rapidly and as of 2012 roughly 14,000 people study or work on campus, about 9,300 of these being Bachelor, Master or PhD students. The environment at modern day EPFL(CH) is highly international with the school attracting students and researchers from all over the world. More than 125 countries are represented on the campus and the university has two official languages, French and English.


EPFL is organised into eight schools, themselves formed of institutes that group research units (laboratories or chairs) around common themes:

School of Basic Sciences (SB, Jan S. Hesthaven)

Institute of Mathematics (MATH, Victor Panaretos)
Institute of Chemical Sciences and Engineering (ISIC, Emsley Lyndon)
Institute of Physics (IPHYS, Harald Brune)
European Centre of Atomic and Molecular Computations (CECAM, Ignacio Pagonabarraga Mora)
Bernoulli Center (CIB, Nicolas Monod)
Biomedical Imaging Research Center (CIBM, Rolf Gruetter)
Interdisciplinary Center for Electron Microscopy (CIME, Cécile Hébert)
Max Planck-EPFL Centre for Molecular Nanosciences and Technology (CMNT, Thomas Rizzo)
Swiss Plasma Center (SPC, Ambrogio Fasoli)
Laboratory of Astrophysics (LASTRO, Jean-Paul Kneib)

School of Engineering (STI, Ali Sayed)

Institute of Electrical Engineering (IEL, Giovanni De Micheli)
Institute of Mechanical Engineering (IGM, Thomas Gmür)
Institute of Materials (IMX, Michaud Véronique)
Institute of Microengineering (IMT, Olivier Martin)
Institute of Bioengineering (IBI, Matthias Lütolf)

School of Architecture, Civil and Environmental Engineering (ENAC, Claudia R. Binder)

Institute of Architecture (IA, Luca Ortelli)
Civil Engineering Institute (IIC, Eugen Brühwiler)
Institute of Urban and Regional Sciences (INTER, Philippe Thalmann)
Environmental Engineering Institute (IIE, David Andrew Barry)

School of Computer and Communication Sciences (IC, James Larus)

Algorithms & Theoretical Computer Science
Artificial Intelligence & Machine Learning
Computational Biology
Computer Architecture & Integrated Systems
Data Management & Information Retrieval
Graphics & Vision
Human-Computer Interaction
Information & Communication Theory
Programming Languages & Formal Methods
Security & Cryptography
Signal & Image Processing

School of Life Sciences (SV, Gisou van der Goot)

Bachelor-Master Teaching Section in Life Sciences and Technologies (SSV)
Brain Mind Institute (BMI, Carmen Sandi)
Institute of Bioengineering (IBI, Melody Swartz)
Swiss Institute for Experimental Cancer Research (ISREC, Douglas Hanahan)
Global Health Institute (GHI, Bruno Lemaitre)
Ten Technology Platforms & Core Facilities (PTECH)
Center for Phenogenomics (CPG)
NCCR Synaptic Bases of Mental Diseases (NCCR-SYNAPSY)

College of Management of Technology (CDM)

Swiss Finance Institute at EPFL (CDM-SFI, Damir Filipovic)
Section of Management of Technology and Entrepreneurship (CDM-PMTE, Daniel Kuhn)
Institute of Technology and Public Policy (CDM-ITPP, Matthias Finger)
Institute of Management of Technology and Entrepreneurship (CDM-MTEI, Ralf Seifert)
Section of Financial Engineering (CDM-IF, Julien Hugonnier)

College of Humanities (CDH, Thomas David)

Human and social sciences teaching program (CDH-SHS, Thomas David)

EPFL Middle East (EME, Dr. Franco Vigliotti)[62]

Section of Energy Management and Sustainability (MES, Prof. Maher Kayal)

In addition to the eight schools there are seven closely related institutions

Swiss Cancer Centre
Center for Biomedical Imaging (CIBM)
Centre for Advanced Modelling Science (CADMOS)
École cantonale d’art de Lausanne (ECAL)
Campus Biotech
Wyss Center for Bio- and Neuro-engineering
Swiss National Supercomputing Centre