Outage probability due to crosstalk from multiple interfering cores in PAM4 inter-datacenter connections

In this work, we propose to use four-level pulse amplitude modulation (PAM4) and multicore fibers (MCFs) to support very high capacity datacenter interconnect (DCI) links. The limitations imposed by inter-core crosstalk (ICXT) on the performance of 112 Gb/s up to 80 km-long optically amplified PAM4 inter-DCI links with intensity-modulation and direct-detection and full chromatic dispersion compensation in the optical domain are analyzed through numerical simulation for high and low skew-symbol rate product (SSRP). With only one interfering core, we show that those PAM4 inter-DCI links achieve an outage probability (OP) of 10−4 with a maximum ICXT level of −13.9 dB for high SSRP and require an ICXT level reduction of about 8.1 dB to achieve the same OP for low SSRP. Due to using full dispersion compensation, for an OP of 10−4, the maximum acceptable ICXT level shows only a 1.4 dB variation with the MCF length increase from 10 km to 80 km. When considering the ICXT induced by several interfering cores, the maximum ICXT level per interfering core for an OP of 10−4 decreases around 3 dB when doubling the number of interfering cores. This conclusion holds for high and low SSRP regimes. For two interfering cores, we show that a single interfering core with low SSRP is enough to induce a severe reduction of the maximum acceptable ICXT level.info:eu-repo/semantics/publishedVersio

Beyond 5G Fronthaul based on FSO Using Spread Spectrum Codes and Graphene Modulators.

High data rate coverage, security, and energy efficiency will play a key role in the continued performance scaling of next-generation mobile systems. Dense, small mobile cells based on a novel network architecture are part of the answer. Motivated by the recent mounting interest in free-space optical (FSO) technologies, this paper addresses a novel mobile fronthaul network architecture based on FSO, spread spectrum codes, and graphene modulators for the creation of dense small cells. The network uses an energy-efficient graphene modulator to send data bits to be coded with spread codes for achieving higher security before their transmission to remote units via high-speed FSO transmitters. Analytical results show the new fronthaul mobile network can accommodate up to 32 remote antennas under error-free transmissions with forward error correction. Furthermore, the modulator is optimized to provide maximum efficiency in terms of energy consumption per bit. The optimization procedure is carried out by optimizing both the amount of graphene used on the ring resonator and the modulator’s design. The optimized graphene modulator is used in the new fronthaul network and requires as low as 4.6 fJ/bit while enabling high-speed performance up to 42.6 GHz and remarkably using one-quarter of graphene only

A Programmable ROADM System for SDM/WDM Networks

This paper proposed and evaluated a programmable ROADM system for MCF-based SDM/WDM networks. The proposed ROADM system employing both bypass connection and Route-and-Select wavelength switching enables adaptable virtual topology in optical networks by dynamically configuring bypass connection cores. The simulation results confirmed this ROADM system could provide acceptable performance with an around 10–20% reduction in the total cost including the number of ports and WSSs by comparing with a fully flexible SDM/WDM ROADM system, which cannot be implemented due to the required extremely high-port-count WSSs

Complexity Versus Accuracy Tradeoffs in Nonlinear Fiber Propagation Models

Some of the most widespread analytical models for nonlinear propagation in fiber optic coherent systems are reviewed, highlighting the tradeoffs between accuracy and complexity in different transmission scenarios, including wide-band optical systems and short-reach links

Advanced DSP Techniques for High-Capacity and Energy-Efficient Optical Fiber Communications

The rapid proliferation of the Internet has been driving communication networks closer and closer to their limits, while available bandwidth is disappearing due to an ever-increasing network load. Over the past decade, optical fiber communication technology has increased per fiber data rate from 10 Tb/s to exceeding 10 Pb/s. The major explosion came after the maturity of coherent detection and advanced digital signal processing (DSP). DSP has played a critical role in accommodating channel impairments mitigation, enabling advanced modulation formats for spectral efficiency transmission and realizing flexible bandwidth. This book aims to explore novel, advanced DSP techniques to enable multi-Tb/s/channel optical transmission to address pressing bandwidth and power-efficiency demands. It provides state-of-the-art advances and future perspectives of DSP as well

Evolution of system embedded optical interconnect in sub-top of rack data center systems

This research was funded by the EU FP7 project “PhoxTrot”, for which it has received funding from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement No. 318240, the Horizon2020 Nephele project (Grant No. 645212), the Horizon2020 COSMICC project (Grant No. 688516).In this paper we review key technological milestones in system embedded optical interconnects in data centers that have been achieved between 2014 and 2020 on major European Union research and development projects. This includes the development of proprietary optically enabled data storage and switch systems and optically enabled data storage and compute subsystems. We report on four optically enabled data center system demonstrators: LightningValley, ThunderValley2, Pegasus and Aurora, which include advanced optical circuits based on polymer waveguides and fibers and proprietary electro-optical connectors. We also report on optically enabled subsystems including Ethernet-connected hard disk drives and microservers. Both are designed in the same pluggable carrier form factor and with embedded optical transceiver and connector interfaces, thus allowing, for the first time, both compute and storage nodes to be optically interchangeable and directly interconnectable over long distances. Finally, we present the Nexus platform, which allows different optically enabled data center test systems and subsystems to be interconnected and comparatively characterized within a data center test environment.Publisher PDFPeer reviewe

Longer Wavelength GaAs-Based VCSELs for Extended-Reach Optical Interconnects

Data centers of today are increasing in size and are built to accommodate strong traffic demands while providing sustainably by having clients sharing resources under one roof. Their massive scale puts pressure on the server network topology and has incited a need for data transmission links that are energy efficient and capable of operation at high bit rates with reach up to a few kilometers. Optical interconnects (OIs) offer large bandwidth and low attenuation at long distances, and are therefore suitable for this task. The most commonly used OIs, with 850 nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) and multi-mode fiber (MMF), have a 25 Gb/s reach that is limited to a few hundred meters. However, the fiber chromatic dispersion and attenuation that limit the OI reach can be reduced significantly by increasing the wavelength of this very same technology. The upper limit of the GaAs-based VCSEL technology, with strained InGaAs quantum wells (QWs), is about 1100 nm.With further improved OI performance, new hyperscale data center topologies can be realized and explored. This will lead to a larger number of possible solutions in traffic engineering as well as for power management. 1060 nm VCSELs could soon open up for lane rates of 100+ Gb/s over distances up to 2 km and help reach the Tb/s link speed aim of data center OI standards, in which capacity is built up mainly by employing multiple parallel lanes, increasing symbol rate by going from binary to four-level pulse amplitude modulation (PAM-4), and optimizing with electrical mitigation techniques such as digital signal processing.In this work we show that 1060 nm GaAs VCSELs are suitable light sources for long-reach OIs by first demonstrating their overall stable performance and capability of error-free data transmission up to 50 Gb/s back-to-back and 25 Gb/s over 1 km of MMF. With PAM-4, we show 100 Gb/s error-free capability over 100 m of MMF, suitable for wavelength division multiplexed OIs that can transmit data at several wavelengths from 850 to 1060 nm over the same fiber channel. We also assemble single-mode 1060 nm VCSEL and single-mode fiber links and demonstrate 50 Gb/s error-free transmission over 1 km using pre-emphasis and 40 Gb/s over 2 km without the use of any electrical mitigation techniques. These results stem from careful VCSEL design, including strained InGaAs QWs with GaAsP barriers, doped AlGaAs distributed Bragg reflectors, a short optical cavity and multiple oxide layers. In addition, we show that the fabrication of such a device poses no increase in complexity and can be realized using standard processing techniques

Optics for AI and AI for Optics

Artificial intelligence is deeply involved in our daily lives via reinforcing the digital transformation of modern economies and infrastructure. It relies on powerful computing clusters, which face bottlenecks of power consumption for both data transmission and intensive computing. Meanwhile, optics (especially optical communications, which underpin today’s telecommunications) is penetrating short-reach connections down to the chip level, thus meeting with AI technology and creating numerous opportunities. This book is about the marriage of optics and AI and how each part can benefit from the other. Optics facilitates on-chip neural networks based on fast optical computing and energy-efficient interconnects and communications. On the other hand, AI enables efficient tools to address the challenges of today’s optical communication networks, which behave in an increasingly complex manner. The book collects contributions from pioneering researchers from both academy and industry to discuss the challenges and solutions in each of the respective fields

Low complexity DSP for high speed optical access networking

A novel low-cost and energy-efficient approach for reaching 40 Gb/s signals is proposed for cost-sensitive optical access networks. Our proposed design is constituted of an innovative low-complex high-performance digital signal processing (DSP) architecture for pulse amplitude modulation (PAM-4), reuses existing commercial cost-effective 10-G components and eliminates the need of a power-hungry radio frequency (RF) component in the transmitter. Using a multi-functional 17-tap reconfigurable adaptive Volterra-based nonlinear equalizer with noise suppression, significant improvement in receiver optical power sensitivity is achieved. Results show that over 30 km of single-mode fiber (SMF) a link power budget of 33 dB is feasible at a bit-error-rate (BER) threshold of 10−3.</jats:p