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

High speed direct modulation of a heterogeneously integrated InP/SOI DFB laser

An integrated laser source to a silicon photonics circuit is an important requirement for optical interconnects. We present direct modulation of a heterogeneously integrated distributed feedback laser on and coupled to a silicon waveguide. We demonstrate a 28 Gb/s pseudo-random bit sequence non-return-to-zero data transmission over 2 km non-zero dispersion shifted fiber with a 1-dB power penalty. Additionally, we show 40-Gb/s duobinary modulation generated using the bandwidth limitation of the laser for both back-to-back and fiber transmission configurations. Furthermore, we investigate the device performance for the pulse amplitude modulation (PAM-4) at 20 GBd for high-speed short-reach applications

A 56 Gbaud Reconfigurable FPGA Feed-Forward Equalizer for Optical Datacenter Networks with flexible Baudrate- and Modulation-Format

The staggering growth of datacenter traffic has spurred the rapid uptake of advanced modulation-formats to increase throughput. Commodity optoelectronic components are used for cost-efficiency, assisted with digital equalizers to mitigate their bandwidth limitations. With optically-switched datacenter architectures gaining momentum, reconfigurable equalizers are sought allowing the receiver to adapt to different fiber lengths, bitrates and modulation-formats associated to different optical paths. An FPGA-based feed-forward equalizer (FFE) reconfigurable in baudrate and modulation-format is demonstrated. We verify its performance with NRZ and PAM-4 experimental data up to 56 GBaud, investigate its accuracy and extract the optimum FFE implementation for different transmission scenarios

A 64 Gb/s PAM-4 linear optical receiver

We present a linear optical receiver realized on 130 nm SiGe BiCMOS. Error-free operation assuming FEC is shown at bitrates up to 64 Gb/s (32Gbaud) with 165 mW power consumption, corresponding to 2.578 pJ/bit

End-to-End Real-Time Demonstration of the Slotted, SDN-Controlled NEPHELE Optical Datacenter Network

The NEPHELE hybrid electro-optical datacenter network (DCN) architecture is proposed as a dynamic network solution to provide high capacity, scalability, and cost efficiency in comparison to the existing DCN infrastructures. The details of the NEPHELE DCN architecture and its various key parts are introduced, and the performance of its implementation is evaluated through an end-to-end NEPHELE demonstrator, which was built at the National Technical University of Athens. Several communication scenarios are demonstrated in real time, exploiting a scalable optical data-plane architecture with a software-defined network (SDN) control plane capable of slotted operation for dynamic allocation of network resources. Real-time end-to-end functionality and integration of various software and hardware components are verified in a six-host prototype datacenter cluster