The Radiation Tolerance of Specific Optical Fibers at -25ºC

This research project seeks to characterize a number of optical fibers in an irradiated, low temperature environment.The purpose of these tests is to qualify suitable fibers for use in the optical links with the high luminosity upgrade of the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN). In the LHC experiments such as ATLAS and CMS, silicon pixel detectors are commonly used to preciselymeasure the trajectories of charged particles. These detectors operate in a high radiation environment and in anambient temperature of -20 to -30ºC to reduce radiation damage to the silicon sensors, hence the requirement of radiation tolerance at low temperatures for the readout optical links in which the fibers are deployed. A number of new fibers, both single-mode and multi-mode, have been selected for their decreased bend sensitivity and improved bandwidth. Given that the LHC luminosity upgrade requirement is much more stringent than these fibers’ originally-intended applications, as well as prior knowledge that radiation induced absorption (RIA) is highly temperature-dependent, the vendor’s specification data will be replaced with our own beam test results. An optical test bench is needed to characterize optical fibers in ionizing radiation from a ⁶⁰Co gamma ray source atthe Brookhaven National Laboratory in February of 2011. Such a multi-channel optical measurement setup is not commercially available and is therefore designed in-house. My task in this research work is to estimate, adjust, and calibrate the dynamic range of the optical power injected into and measured from the fibers. Multiple 850nm VCSEL laser are used as the sources and TI OPT101 chips are used as the detectors; one laser and one chip will beused per fiber in the multi-channel setup. The dynamic range for each can be shifted up or down by altering the voltage supplied to the detector and the current supplied to the laser. The calibration process, LabVIEW routine, design and construction of the chamber, final irradiation tests on the fibers, and experimental results will be presented. My research contributes to the optical link R&D project with theFermi National Laboratory, Oxford University, and CERN, and my work progress is integrated into the project flow of this international collaborative group