Radiation Resistance of Ge-doped Multi-Mode Fiber for Optical Links in Collider Experiments

TL;DR

This work evaluates radiation hardness of Ge-doped multimode telecom fibers for high-energy physics optical links. Using a Co-60 gamma irradiation setup, the authors measure Radiation-Induced Attenuation (RIA) as a function of total ionizing dose $TID$ across dose rates and temperatures, with annealing after shielding. They identify two non-radhard fibers with linear RIA growth and two radiation-resistant fibers that maintain very low RIAs, achieving $RIA \approx 0.05~\mathrm{dB/m}$ at a total dose of $300~\mathrm{kGy(SiO_2)}$. The findings indicate that appropriate Ge-doped fiber fabrication and post-irradiation annealing enable stable optical links under LHC-like radiation, supporting deployment in collider experiments.

Abstract

The applications of optical links in collider experiments provide the advantage of high-speed data transmission with low mass fibers over distances of a few hundred meters. Ge-doped multi-mode fibers are evaluated for radiation tolerance in ionizing doses of Co-60 gamma rays. The Radiation-Induced Attenuation (RIA) varies significantly depending on doping substances and fabrication technologies. A type of telecom-grade fiber has demonstrated an RIA of 0.05 dB/m under a total ionizing dose of 300 kGy(SiO2). The dependence on dose rate is compared in the range between 5 Gy/hr and 1.4 kGy/hr, and the annealing recovery is observed after the Co-60 source is shielded. The temperature dependence is investigated across a range of -15 oC to room temperature. At cold temperatures, stagnant annealing leads to a substantially higher RIA during irradiation. The recovery of radiation-induced defects is typically within a few hours, resulting in similar RIA levels regardless of the dose rate and temperature during exposure. Ge-doped fibers of chosen fabrication methods are capable of enduring high ionizing doses for use in high-energy physics experiments.

Figures (6)

• Figure 1: Bare-fiber reels were sealed in a water tank with fiber ends connected by 40 m patch cords to Anritsu CMA5 laser sources. The transmission of laser light was returned and measured by an EXPO LTB1 power meter. The sealed fiber samples had thermal couples attached inside to record temperatures by MCR-4TC.
• Figure 2: Two types of Ge-doped fibers (Type-B, O) exhibited significant transmission losses when exposed to ionizing radiation. The Co-60 irradiation tests were conducted at a dose rate of 33.7 Gy/hr, at -15 °C. The fiber samples were immersed in a compressor-chilled water tank. The temperature deviated by $\pm$2$^\circ$ due to the control latch switching periodically. The RIAs measured during irradiation (solid line) and subsequently in annealing with the Co-60 shielded (dashed line) are plotted.
• Figure 3: Samples of two non-radiation hard fiber types were tested under dose rates from 2.8 to 39 Gy/hr at temperatures of -15$^\circ$ and 15$^\circ$. The dashed lines are the instant RIAs at daily accumulated doses, while the markers denote the corresponding RIAs after 10 hours of annealing. The RIA increased linearly with TID, showing little annealing recovery. The overlapping of data points of different samples suggest minimal dependencies on dose rate and temperature.
• Figure 4: RIA measurements are plotted for two types of radiation-resistant Ge-doped fibers in the initial days at dose rates of a) 6 Gy/hr and b) 1.43 kGy/hr, at 32 °C. The solid lines were recorded under irradiation, and the dashed lines were the annealing with the Co-60 being shielded. At a dose rate of 1.43 kGy/hr, the radiation had heated up the water tank by 1$^\circ$. The instant RIAs are twice higher than those of the annealed for both fiber types.
• Figure 5: The radiation dose rate of around 30 Gy/hr is compatible with the conditions at the LHC. The RIA measurements of radiation-resistant fibers were conducted at a) -15$^\circ$ and b) 13$^\circ$, in initial days during irradiation (solid lines) and in annealing with the Co-60 source shielded (dashed lines). The samples immersed in water tanks were chilled by a compressor, with temperatures deviating due to the control latch switching periodically. In cold (-15$^\circ$), the RIAs in radiation deviated with temperature, and the stagnant recovery had the RIA levels twice higher than at 13$^\circ$.