Alex Worrall

960 Gb/s Optical Backplane Ecosystem Using Embedded Polymer Waveguides and Demonstration in a 12G SAS Storage Array

An optical backplane ecosystem is described and demonstrated that is capable of multi-Tb/s bandwidth and is based on embedded polymer waveguides, passive optical backplane connectors, and midboard optical transceivers with bandwidth up to 28 Gb/s per lane. These systems provide the highest bandwidth-density, lowest power consumption, while maintaining the signal integrity. Ecosystems built around this architecture will provide the bandwidth-density required for next generation fabric interconnect for storage, switching, and routing applications in future high capacity generations of Data Centers and HPC systems. To demonstrate the applicability of this technology, it was used to provide embedded optical connectivity within a functional data storage enclosure.

Pluggable Electro-Optical Circuit Board Interconnect Based on Embedded Graded-Index Planar Glass Waveguides

Widespread adoption of electro-optical circuit boards based on embedded glass waveguide technology would enable seamless optical connectivity from external fiber-optic networks to system embedded optical interconnect architectures. In this paper, we report on the fabrication of planar multimode waveguides within thin glass foils based on a two-step thermal ion exchange process. Novel lamination techniques were developed to allow glass waveguide panels to be reliably integrated into a conventional electronic multilayer printed circuit board. In addition, a complete suite of optical connector technologies were developed to enable both direct fiber-to-board and board-to-board connectivity. We present the design, development, and characterization of a fully integrated connection platform, comprising a 281×233 mm2 multilayer electro-optical backplane with integrated planar glass waveguides, a pluggable connector system, and five pluggable test cards. Both on-card and externally generated 850 and 1310-nm optical test data were conveyed through the connector and waveguide system and characterised for in-system and system-to-system optical connectivity at data rates up to 32 Gb/s per channel exhibiting bit error rates of less than 10-12.

Demonstration of fully enabled data center subsystem with embedded optical interconnect

The evolution of data storage communication protocols and corresponding in-system bandwidth densities is set to impose prohibitive cost and performance constraints on future data storage system designs, fuelling proposals for hybrid electronic and optical architectures in data centers. The migration of optical interconnect into the system enclosure itself can substantially mitigate the communications bottlenecks resulting from both the increase in data rate and internal interconnect link lengths. In order to assess the viability of embedding optical links within prevailing data storage architectures, we present the design and assembly of a fully operational data storage array platform, in which all internal high speed links have been implemented optically. This required the deployment of mid-board optical transceivers, an electro-optical midplane and proprietary pluggable optical connectors for storage devices. We present the design of a high density optical layout to accommodate the midplane interconnect requirements of a data storage enclosure with support for 24 Small Form Factor (SFF) solid state or rotating disk drives and the design of a proprietary optical connector and interface cards, enabling standard drives to be plugged into an electro-optical midplane. Crucially, we have also modified the platform to accommodate longer optical interconnect lengths up to 50 meters in order to investigate future datacenter architectures based on disaggregation of modular subsystems. The optically enabled data storage system has been fully validated for both 6 Gb/s and 12 Gb/s SAS data traffic conveyed along internal optical links.

Planar polymer and glass graded index waveguides for data center applications

Embedded optical waveguide technology for optical printed circuit boards (OPCBs) has advanced considerably over the past decade both in terms of materials and achievable waveguide structures. Two distinct classes of planar graded index multimode waveguide have recently emerged based on polymer and glass materials. We report on the suitability of graded index polymer waveguides, fabricated using the Mosquito method, and graded index glass waveguides, fabricated using ion diffusion on thin glass foils, for deployment within future data center environments as part of an optically disaggregated architecture. To this end, we first characterize the wavelength dependent performance of different waveguide types to assess their suitability with respect to two dominant emerging multimode transceiver classes based on directly modulated 850 nm VCSELs and 1310 silicon photonics devices. Furthermore we connect the different waveguide types into an optically disaggregated data storage system and characterize their performance with respect to different common high speed data protocols used at the intra and inter rack level including 10 Gb Ethernet and Serial Attached SCSI.

International standardisation of optical circuit board measurement and fabrication procedures

Widespread adoption of optical circuit boards will herald substantial performance, environmental and cost benefits for the data communications industry. Though optical circuit board technology has advanced considerably over the past decade, commercial maturity will be gated by the availability of conformity standards to forge future quality assurance procedures. One important prerequisite to this is a reliable test and measurement definition system, which is agnostic to the type of waveguide system under test and therefore can be applied to different optical circuit board technologies as well as being adaptable to future variants. A serious and common problem with the measurement of optical waveguide systems has been lack of proper definition of the measurement conditions for a given test regime, and consequently strong inconsistencies ensue in the results of measurements by different parties on the same test sample. We report on the development of a new measurement identification standard to force testers to capture sufficient information about the measurement conditions for a given optical circuit board such as to ensure consistency of measurement results within an acceptable margin. Furthermore we demonstrate how the application of the measurement identification system can bring about a dramatic improvement in results consistency, by comparative evaluation of the results on multimode polymer waveguide based optical circuit test boards from a large selection of testing organisations.

Converged photonic data storage and switch platform for exascale disaggregated data centers

We report on a converged optically enabled Ethernet storage, switch and compute platform, which could support future disaggregated data center architectures. The platform includes optically enabled Ethernet switch controllers, an advanced electro-optical midplane and optically interchangeable generic end node devices. We demonstrate system level performance using optically enabled Ethernet disk drives and micro-servers across optical links of varied lengths.

Polymer optical waveguides with reduced in-plane bend loss for electro-optical PCBs

In-plane bend loss represents the greatest commercial inhibitor to deploying multimode optical waveguides on densely populated electro-optical printed circuit boards (OPCB) as the minimum bend radii currently possible are too large to be practical in common designs. We present a concept and fabrication method for creating novel polymer optical waveguide structures with reduced bend losses to enable higher density routing on an OPCB. These nested core waveguide structures comprise a core surrounded by a thin shell of cladding, which allows for two-fold modal containment by first a conventional low refractive index contrast (LIC) boundary followed by a secondary high refractive index contrast (HIC) boundary. The purpose of this is to reduce the in-plane bend losses incurred on tightly routed optical channels, while not incurring prohibitive dispersion, sidewall scattering and optical crosstalk penalties. We have designed and fabricated nested core multimode polymer waveguides, evaluated their performance in comparison to conventional step-index waveguides and simulated these structures using the beam propagation method. Preliminary results are presented of our measurements and simulations