Sep 25 – 29, 2006
Valencia, Spain
Europe/Zurich timezone

Bandwidth of Micro-Twisted Cables and Spliced SIMM/GRIN Fibers and Radiation Hardness of PIN/VCSEL Arrays

Sep 27, 2006, 12:35 PM
Valencia, Spain

Valencia, Spain

IFIC – Instituto de Fisica Corpuscular Edificio Institutos de Investgación Apartado de Correos 22085 E-46071 València SPAIN


Kock Kiam Gan (The Ohio State University)


We study the feasibility of fabricating an optical link for the SLHC ATLAS silicon tracker based on the curret pixel optical link architecture. The electrical signal between the current pixel modules and the optical modules is transmitted via micro-twisted cables. The optical signal between the optical modules and the data acquisition system is transmitted via rad-hard SIMM fibers spliced to rad-tolerant GRIN fibers. The link has several nice features. We will present the result of a study of the bandwidth of the link and an irradiation of PIN/VCSEL arrays with 24 GeV protons at CERN to SLHC dosages.


The SLHC is designed to increase the luminosity of the LHC by a factor of ten to 10^35 /cm^2/s. The optical
components of the present pixel detector are mounted on patch panels (PP0) instead of directly on the pixel
modules. The radiation level at the optical link location is also expected to increase by a factor of ten. After
five years of operation at the SLHC, we expect a silicon component (e.g. ASIC and PIN) of the optical link to be
exposed to a maximum total fluence of 2.5 x 10^15 1-MeV neq/cm^2. The corresponding fluence for a GaAs
component (e.g. VCSEL) is 1.4 x 10^16 1-MeV neq/cm^2.
In the present pixel detector, the electrical signal between the pixel modules and the optical modules (opto-
boards) is transmitted via ~ 1 m of micro twisted cables. The opto-boards contain optical packages with PIN
and VCSEL arrays to receive and transmit optical signal. Each array in an package couples to a rather robust
fiber ribbon with a removable MT connector. Each ribbon consists of 8 m of rad-hard SIMM fibers spliced to
70 m of rad-tolerant GRIN fibers.
The design of the present pixel optical links has several nice features:
• Much reduced radiation level: Since the optical components are mounted on PP0 instead of directly on the
pixel modules, the radiation exposure is much reduced.
• Separation of pixel modules and opto-boards production: The separation of the opto-boards from the pixel
modules decouples the production of both components and greatly simplifies their design and fabrication.
• Removable and robust fiber ribbon: An optical package on a pixel opto-board couples to a removable and
robust 8-channel fiber ribbon terminated with an MT connector.
For the SLHC, we would like to take advantage of the several years of R&D that produced this design.
We currently transmit optical signals at 80 Mb/s and expect to transmit signals at ~ 1 Gb/s at the SLHC. We
have studied the feasibility of an upgrade for the silicon tracker based on the present architecture. If the
present architecture can transmit signals at the higher speed, the constrain of requiring no extra service space
is automatically satisfied. We will present our measurement of the bandwidth of the micro-twisted cables and
the spliced SIMM to GRIN fiber ribbon. In addition, we will present the results on irradiation with 24 GeV
protons at CERN to SLHC dosages for candidate PIN and VCSEL arrays from various vendors, including
measurements of the single event upset (SEU) rates.

Primary author

Kock Kiam Gan (The Ohio State University)

Presentation materials