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

Abstract

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 opticalinterconnect 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.

Low Cost 100 Gbps Multicore VCSEL Based Transmitter Module Platform

“…A 1x4 VCSEL array is directly coupled to a 3D glass interposer fabricated using ultrafast laser inscription (ULI) [7], a well-established technique to embed 3D waveguides in a glass interposer. Thanks to this technique a 'fan-out' structure can be easily achieved from the linear arrangement of the VCSELs to the cylindrical geometry of the MCF [8]. Error free operation of 3 of the 4 VCSEL channels at 25 Gbps per lane is presented.…”

112 Gb/s sub-cycle 16-QAM Nyquist-SCM for intra-datacenter connectivity

“…The feasibility of serial 100 Gb/s connectivity using non-return-to-zero (NRZ) modulation has been demonstrated in 4 based on specialized stateof-the-art photonics and electronics technologies, but, in order to reach the cost and energy consumption targets for future systems, implementation with available CMOS nodes is an outright requirement. With CMOS speeds unable to keep pace with surging interconnect lane speeds, there is growing consensus among academia and industry towards migration to higher-order modulation (HOM) providing more bits-per-symbol 3,5 .…”

Scaling single-wavelength optical interconnects to 180 Gb/s with PAM-M and pulse shaping

“…Serial 100 Gb/s connectivity presents a formidable challenge, as it requires state-of-the-art high-bandwidth electronics, optics and printed circuit boards (PCBs) which currently struggle to cope with the extremely cost-sensitive requirements of the datacenter ecosystem. To circumvent this obstacle, higher-order modulation (HOM) is gaining momentum 4,5 . Providing more bits-per-symbol, HOM decouples the aggregate bitrate of the optical interconnect link with the speed capabilities of available CMOS nodes and the bandwidth of commodity optics such as DMLs and EMLs.…”