Effects of e-beam and gamma sterilization on attenuation of selected single-mode and mutimode optical fibers

Abstract

Sterilization of medical equipment using e-beam or gamma radiation produces high sterility assurance but may lead to alterations in materials being treated. Thus, color centers developed in optical fibers result in added attenuation. In this work a series of specialty single-mode (SM) and multimode (MM) optical fibers (13 in total) were exposed to gamma and e-beam sterilization doses of 32 kGy, and the radiation-induced attenuation was investigated. The optical fibers selected for the study had different core chemical compositions, including pure silica and also SiO2 doped with Ge, F, P and Al. The fibers also differed in the clad diameters (80 and 125 μm), numerical aperture (0.1 – 0.21), coating types (carbon, acrylate, polyimide) and the cutoff wavelength (SM fibers only, 930 – 1470 nm). Effects of all these features on the radiation-induced attenuation were analyzed primarily in the framework of medical applications. The radiation-induced optical losses can be moderated by subsequent thermal treatment of the fibers, and such option was also investigated. Our results showed that while the radiation-induced losses may be high (102 – 104 dB/km), sterilization using e-beam and gamma radiation can be acceptable for many medical applications that deploy 3 m or less fiber lengths. After gamma or e-beam sterilization, 3 meters length of SM fibers with pure SiO2 and Ge doped core transmit >98% of optical power at 1550 and 1310 nm. In contrast, similar length of SM fibers with P and Al doped cores exhibit very low transmission and cannot be used after ionizing sterilization. Among the MM fiber, F-doped core fibers display much higher transmission than Ge-core fibers, especially at 850 nm. The clad diameter, coating type and bend insensitive features in the refractive index profile did not show much effect on the radiation-induced loss. While gamma and e-beam radiation caused similar changes in the attenuation spectra, gamma radiation caused ~25% higher loss increase than e-beam at the same 32 kGy dose. Since our data showed that postradiation annealing at 100°C for 24 hours results in only ~30% recovery of the radiation induced loss, it may not be practical to implement such annealing scheme for medical applications.