New Possibilities: UV LEDs and lasers are more cost effective than deuterium and xenon lamps. As a result, optical fibres are becoming more and more interesting for UV transmission.
Three criteria are crucial in deciding which fibre is suitable for which application:
1. Initial Attenuation
The attenuation of a new fibre prior to UV irradiation depends on the wavelength and is typically provided in dB/km.
2. Solarization
Solarization refers to attenuation caused by UV radiation. The greatest impairment occurs at wavelengths below 250 nm. The damage is particularly significant at about 214 nm. The magnitude of these additional losses strongly depends on the fibre type.
3. Stability after UV Irradiation
After irradiation, some of the initial solarization damage recedes after a few hours. The condition of the fibre after regeneration remains permanent.
Standard high-OH fibres for Vis transmission exhibit relatively low attenuation in the UV spectrum as well.
Inexpensive standard UV fibres: The core of a high-OH fibre has been modified to exhibit improved properties under UV light.
In FVP UVM fibres that have been enriched with hydrogen and that exhibit optimal properties for UV light, the hydrogen enrichment is lost again after a short time. The lifetime can be extended considerably by cooling or by using a large core diametre.
Solarization-resistant fibres used in the deep UV (190 nm) do not have limitations in performance and lifetime, even without cooling.
