Radiation characteristics of optical fibers

Recently, the radiation characteristics of various optical fibers have been examined, but those of single mode fibers have been rarely reported. The authors examined the radiation characteristics of the single mode fibers prepared by VAD (vapor axial deposition) method to compare them with those of multi-mode fibers. The fibers prepared are: (A) Ge-doped quartz glass core, highly pure quartz glass clad and (B) OH-doped quartz glass core, F-doped quartz glass clad as the single mode fibers, and (C) Ge and P-doped quartz glass core and quartz glass clad and (D) Ge-doped quartz glass core and quartz glass clad as the GI fibers. Those were irradiated with 60Co γ-ray at 2.7 x 104 rad/h to examine the increase of loss. For the element fibers of these, the loss spectra in infrared region were also measured with a monochromator after they had been left for 4 hours in a furnace at 200 deg C through which only hydrogen gas flowed and cooled. Both the samples (A) and (B) increased the loss with the increase of radiation dose, and the increase tended to saturate at 5 x 105 Rad. The radiation characteristics of the sample (B) were inferior, and this was the exact opposite to the result which has so far been obtained in multi-mode fibers. The increase of loss at 850 nm in the sample (C) was about 17 times as large as the sample (D) in the results for the GI fibers. This shows that the effect of phosphorus was more remarkable than that of germanium because the Ge content in both samples (C) and (D) was almost the same. (Wakatsuki, Y)