Sep 26 – 30, 2011
Vienna, Austria
Europe/Zurich timezone

The Versatile Link Common Project: Feasibility Report

Sep 29, 2011, 9:50 AM
Room EI 8 (Vienna, Austria)

Room EI 8

Vienna, Austria

<font face="Verdana" size="2"><b>Vienna University of Technology</b> Department of Electrical Engineering Gusshausstraße 27-29 1040 Vienna, Austria


Mr Francois Vasey (CERN)


The Versatile Link is a bi-directional digital optical data link operating at rates up to 4.8 Gbit/s and featuring radiation resistant low power and low mass front-end components. The system is developed in multimode or singlemode versions operating at 850nm or 1310nm wavelength respectively. It has serial data interfaces and is protocol-agnostic, but is targeted to operate in tandem with the GigaBit Transceiver (GBT) serializer/deserializer chip. This presentation will give an overview of the project status 3.5 years after its launch. It will describe the encountered challenges and highlight the solutions proposed at the system as well as component level. It will conclude with a positive feasibility assesment and an outlook of future project development possibilities.

Summary 500 words

The Versatile Link is a joint ATLAS-CMS project, launched in April 2008 and due to be completed in September 2012. It is broken down in 4 concurrent workpackages, one at the system level and three at the component level (front-end components, back-end components and passive components). This presentation will report on the completion of the second project phase assessing feasibility. It will give a broad project overview, while leaving most of the technical details to additional contributions presented by the individual workpackages.
The Versatile Link system is a bi-directional digital optical data link operating at rates up to 4.8 Gbit/s over a distance of typically 100m. It is described by a coherent set of specifications covering components and system, as well as system-level power and jitter budget tables. These specifications and tables will be presented and discussed, highlighting in particular the margins included to account for radiation-induced performance degradation and other penalties.
In a basic point-to-point configuration, the link is driven by two transceivers, one at each end. The form factor for the Versatile Link transceiver was selected early on to be SFP+. This choice allowed a quick determination of the test system interfaces. It also contributed to narrowing down the choice of commercial module types to be evaluated as reference components. Carrier boards for SFP+ modules have been built and distributed to project partners. Test setups with 10Gbps capabilities are now available at CERN, FNAL and SMU. In addition to full fledged 12G commercial BER testers, custom BER testers based on Xilinx and Altera FPGA evaluation platforms have been built, allowing testing of not only the basic BER but also of the performance of proposed Forward Error Correction (FEC) codes and protocols. Routinely performed characterization and comparative tests will be presented. They confirm that a wide range of front-end and back-end components comply to the Versatile Link functional specifications, but also indicate a few cases where power margins may be tight. In addition to these results, the possible use of dense optical arrays at the backend will be mentioned, and a few implementation examples will be shown.
Whereas the transceiver located at the Versatile Link backend can be a standard commercial device, the front-end transceiver must withstand radiation, operate in a magnetic field and be as low mass as possible. The SFP+ module to be developed for the Versatile Link front-end thus needs to be customized to include a radiation hardened transceiver chipset along with a radiation-qualified laser diode and photodiode. The module housing must also be customized to reduce as much as possible its material while maintaining both EMI susceptibility and emission within acceptable limits. Versatile Transceiver prototypes fullfilling functional and environmental requirements will be presented.
The Versatile Link is developed in multimode (MM) or singlemode versions (SM) operating at 850nm or 1310nm wavelength respectively. SM as well as MM fibre samples have been tested during several gamma irradiation runs. Significant temperature effects on the radiation induced fibre absorption (RIA) have been observed. Cold irradiations (representative of a typical tracker operating temperature of -20 deg C) of candidate fibres have been carried out to full HL-LHC doses and at various rates. Radiation test results of SM as well as MM fibres and connectors will be shown.
To conclude, the feasibility of the Versatile Link system will be assessed and an outlook will be given pointing at future project development possibilities.

Primary author


Mr Alan Prosser (FNAL) Mrs Annie Xiang (Southern Methodist University) Mr Jan Troska (CERN) Mr Jingbo Ye (Southern Methodist University) Mr Simon Kwan (FNAL) Mr Todd Huffman (University of Oxford) Mr Tony Weidberg (University of Oxford)

Presentation materials