2 Fiber Optics & Optical Fiber Fluorescence in Fiber Optical Materials Fused silica glass, especially the lower -OH types, can exhibit fluorescence when illuminated with 254nm light with a Schott UG-5 glass filter. From Heraeus Amersil data, this apparently does not occur in the High -OH materials in the Suprasil® family. Slight blue to blue-violet appears in materials such as Homosil®, Herasil®, Infrasil® and HOQ 310. Quartz glass is free from visible fluorescence at excitation wavelength greater than 290nm. Some varieties of sapphire have been reported to exhibit fluorescence under UV excitation. Cladding and buffer materials used in the manufacturing of optical fiber may exhibit similar emission characteristics under some types of excitation, UV, soft X-ray or energetic particles. Polymicro offers a variety of fiber types that use low fluorescence silica.
UV Fiber Performance (Solarization) Polymicro manufactures several categories of silica fibers that are capable of operation in the UV wavelength range. These include: 1)
FVP (Standard High -OH)
2)
FVP-UVM (Modified Core High -OH)
3)
FVP-UVMI (Hydrogen Loaded UVM)
4)
FDP (Deep UV Fiber)
In selecting the best product for a UV application, there are 3 main performance criteria that should be considered. These are: 1)
Initial Attenuation.
2)
Additional attenuation caused by UV radiation.
3)
Stability following initial UV degradation.
Initial Attenuation. This is the attenuation as a function of wavelength for new fiber prior to any UV exposure. This is typically measured in dB/km, and it can be changed to dB/m by dividing by 1000. Figure 2-21 below shows a typical initial attenuation for all of Polymicro’s UV products. UV Induced Additional Attenuation. This is the damage induced by exposure to UV radiation. It is commonly known as solarization. Most of this damage occurs at wavelengths less than 250nm, with peak damage occurring at approximately 214nm. The degree of damage varies greatly with the type of fiber. Figure 2-22 shows typical solarization levels as a function of time for various Polymicro UV products as shown in linear units for 1m length. Figure 2-23 shows comparison of 4hr exposure levels as a function of wavelength. Typically, this additional attenuation is measured in units of dB/m and is scalable to any length. FVP-UVM fiber has improved performance compared to the standard High -OH FVP fiber. The hydrogen loaded fiber, FVP-UVMI, has almost no degradation, but this fiber has a limited lifetime and eventually reverts to typical FVP-UVM performance. This lifetime can be extended by keeping the fiber refrigerated and by using larger diameter fibers. The deep-UV enhanced FDP fiber has low solarization degradation, but with no limit on lifetime and no need for refrigeration. Figure 2-21 Typical Attenuation of Polymicro High -OH UV Fiber Products
Herasil®, Homosil®, Infrasil® and Suprasil® are registered trademarks of Heraeus Quarzglas GmbH & Co.
© Polymicro Technologies, a Subsidiary of molex.
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