Adaptive optical interconnects: The ADDAPT project

Existing optical networks are driven by dynamic user and application demands but operate statically at their maximum performance. Thus, optical links do not offer much adaptability and are not very energy-effcient. In this paper a novel approach of implementing performance and power adaptivity from system down to optical device, electrical circuit and transistor level is proposed. Depending on the actual data load, the number of activated link paths and individual device parameters like bandwidth, clock rate, modulation format and gain are adapted to enable lowering the components supply power. This enables exible energy-efficient optical transmission links which pave the way for massive reductions of CO2 emission and operating costs in data center and high performance computing applications. Within the FP7 research project Adaptive Data and Power Aware Transceivers for Optical Communications (ADDAPT) dynamic high-speed energy-efficent transceiver subsystems are developed for short-range optical interconnects taking up new adaptive technologies and methods. The research of eight partners from industry, research and education spanning seven European countries includes the investigation of several adaptive control types and algorithms, the development of a full transceiver system, the design and fabrication of optical components and integrated circuits as well as the development of high-speed, low-loss packaging solutions. This paper describes and discusses the idea of ADDAPT and provides an overview about the latest research results in this field

Photonic integration enabling new multiplexing concepts in optical board-to-board and rack-to-rack interconnects

New broadband applications are causing the datacenters to proliferate, raising the bar for higher interconnection speeds. So far, optical board-to-board and rack-to-rack interconnects relied primarily on low-cost commodity optical components assembled in a single package. Although this concept proved successful in the first generations of optical-interconnect modules, scalability is a daunting issue as signaling rates extend beyond 25 Gb/s. In this paper we present our work towards the development of two technology platforms for migration beyond Infiniband enhanced data rate (EDR), introducing new concepts in board-to-board and rack-to-rack interconnects. The first platform is developed in the framework of MIRAGE European project and relies on proven VCSEL technology, exploiting the inherent cost, yield, reliability and power consumption advantages of VCSELs. Wavelength multiplexing, PAM-4 modulation and multi-core fiber (MCF) multiplexing are introduced by combining VCSELs with integrated Si and glass photonics as well as BiCMOS electronics. An in-plane MCF-to-SOI interface is demonstrated, allowing coupling from the MCF cores to 340x400 nm Si waveguides. Development of a low-power VCSEL driver with integrated feed-forward equalizer is reported, allowing PAM-4 modulation of a bandwidth-limited VCSEL beyond 25 Gbaud. The second platform, developed within the frames of the European project PHOXTROT, considers the use of modulation formats of increased complexity in the context of optical interconnects. Powered by the evolution of DSP technology and towards an integration path between inter and intra datacenter traffic, this platform investigates optical interconnection system concepts capable to support 16QAM 40GBd data traffic, exploiting the advancements of silicon and polymer technologies

Free-space optics for high speed reconfigurable card-to-card optical interconnects

High-speed card-to-card optical interconnects are highly demanded in high-performance computing and data centers. Compared with other solutions, free-space optical interconnects have the capability of providing both reconfigurability and flexibility. In this paper we propose and experimentally demonstrate a free-space based reconfigurable optical interconnect architecture and it is capable of connecting cards located both inside the same rack as well as in different racks. Results show that 3xiO Gb/s data transmission is achieved with a worst-case receiver sensitivity better than -9.38 dBm

On the benefits of resource disaggregation for virtual data centre provisioning in optical data centres

Virtual Data Centre (VDC) allocation requires the provisioning of both computing and network resources. Their joint provisioning allows for an optimal utilization of the physical Data Centre (DC) infrastructure resources. However, traditional DCs can suffer from computing resource underutilization due to the rigid capacity configurations of the server units, resulting in high computing resource fragmentation across the DC servers. To overcome these limitations, the disaggregated DC paradigm has been recently introduced. Thanks to resource disaggregation, it is possible to allocate the exact amount of resources needed to provision a VDC instance. In this paper, we focus on the static planning of a shared optically interconnected disaggregated DC infrastructure to support a known set of VDC instances to be deployed on top. To this end, we provide optimal and sub-optimal techniques to determine the necessary capacity (both in terms of computing and network resources) required to support the expected set of VDC demands. Next, we quantitatively evaluate the benefits yielded by the disaggregated DC paradigm in front of traditional DC architectures, considering various VDC profiles and Data Centre Network (DCN) topologies.Peer ReviewedPostprint (author's final draft

Performance of reconfigurable free-space card-to-card optical interconnects under atmospheric turbulence

Free-space based card-to-card optical interconnects are promising candidates for the provision of parallel high-speed and reconfigurable interconnectivity in data-centers and high-performance computing clusters. However, the atmospheric turbulence may degrade the interconnect performance due to the beam wander, signal scintillation, and beam broadening effects. In this paper, the experimental investigation of the impact of both moderate and comparatively strong atmospheric turbulence on the bit-error-rate (BER) performance of our proposed reconfigurable free-space card-to-card optical interconnects is presented. Experimental results show that the BER performance does suffer power penalties of ∼0.5 dB and ∼1.6 dB at BER of 10 -9 under moderate and strong levels of turbulence respectively

Experimental demonstration of high-speed full-duplex reconfigurable free-space card-to-card optical interconnects

A high-speed full-duplex free space based card-to-card optical interconnect architecture with flexibility and reconfigurablity is proposed and experimentally demonstrated. 3×3 10Gb/s data transmission for up to 30cm is achieved with receiver sensitivity better than -11.5dBm

Bandwidth enhancement in multimode polymer waveguides using waveguide layout for optical printed circuit boards

© 2016 OSA. Dispersion studies demonstrate that waveguide layout can be used to enhance the bandwidth performance of multimode polymer waveguides for use in board-level optical interconnects, providing >40 GHz×m without the need for any launch conditioning.The authors would like to acknowledge Dow Corning for providing the waveguide samples and EPSRC for supporting the work. Additional data related to this publication is available at the University of Cambridge data repository (https://www.repository.cam.ac.uk/handle/1810/251390)

PERFORMANCE ASSESSMENT OF SCHEDULERS IN OPTICAL INTERCONNECTION NETWORKS

With ever-increasing demand for high-performance computing systems, interconnection networks, serving as the communication links in multicore architectures have become a key element for guaranteeing the system performance. Compared with bandwidth-limited power hungry electrical interconnection networks, optical integrated interconnection networks also referred to as networks-on-chip (ONoC) architectures are emerging as a promising alternative to enable future computing performance. In ONoC architectures, scheduling algorithms are necessary for avoiding packet collisions while achieving high throughput, low latency, and good fairness. Scheduling algorithms exist for non-blocking electrical NoC. These algorithms can be applied to ONoC, while accounting for additional constraints arising from optical component limitations. In this thesis various scheduling algorithms are simulated, With the objective of comparing their latency and throughput using C + + programming language for ONoC with bus and ring topologies. An optimal scheduler based on two-step scheduling (TSS) technique is proposed. The optimal TSS models the scheduling problem in two steps for ONoC. The first step is the matching step which is done by representing each node pair as input bipartite graph then matching takes place between the input and output ports. The second step performs the wavelength assignment between each paired node while avoiding collisions and also with the consideration of wavelength continuity. The two-step approach with the iSLIP and MWM algorithms are considered. The proposed optimal TSS is simulated and its performances are evaluated. The optimal scheduler with maximum weighted matching (MWM) scheduling policy achieves better results in comparison to iSLIP scheduling policy based on queue length under any packet arrival process. The optimal MWM scheduling policy achieved better performance for both bus and ring topologies. The main result is that unidirectional ring topology outperforms the bus topology for any number of wavelengths less or equal to the number of ONoC port, even if the average path length is longer. The reason is that in the bus topology half of the wavelengths are allocated in each direction, fixing the maximum number of packets in each direction using two transceivers per node can compensate this issue, reaching to better performance than the ring