30 years of UV fibers: past and trends

Multimode UV fibers with a high-OH synthetic silica core and F-doped silica cladding have been available for over 50 years. Initially, their use was limited to wavelengths above 250 nm due to UV-absorbing defect centers that hindered reliable transmission at shorter wavelengths. Advances in preform and fiber manufacturing, along with additional treatments, significantly improved their performance over the past decade. Now, the DIN 58145 standard provides a method to quantify solarization in fibers for various applications. Using a deuterium lamp, this standardized approach induces UV damage over four hours, enabling comparisons of UV transmission and solarization starting at 185nm. Studies on solarization from pulsed UV lasers, particularly Nd:YAG lasers at 213 nm, 266 nm, and 355 nm, have revealed defect generation, annealing, and transfer mechanisms. The resulting UV-induced losses can be modeled with Gaussianshaped absorption bands, where peak values (amplitudes), central wavelengths, and FWHM are adjusted for optimal fitting. Current trends include advancements in preform techniques, hermetic coatings with hydrogen loading, and improvements in hydrogen-free, low-OH fibers for better temperature and UV resistance. Finally, innovations in side-illuminating fibers and long-length applications will be presented.