An optical fiber bundle unit is provided for transmitting ultraviolet light in
which the increase of the transmission loss caused by radicals generated in the
optical fiber by irradiation or transmission of ultraviolet light is suppressed
and a stable energy state is maintained even after the irradiation or transmission
of ultraviolet light. The optical fiber bundle unit for transmitting ultraviolet
light includes an optical fiber bundle and a sealed container in which the optical
fiber bundle is held, wherein the sealed container contains a hydrogen gas.
