Radiation-induced transmission loss in Low Water Peak Single Mode (LWPSM) fiber has been investigated. Formation
and conversion processes of defect centers also have been proposed using electron spin resonance in the fiber irradiated
with gamma rays. When the irradiation dose is low, Germanium electron center (GEC) and self-trapped hole center
(STH) occur. With the increase of dose, E’ centers (Si and Ge) and nonbridge oxygen hole centers (NBOHCs) generate.
With the help of thermal-bleaching or photo-bleaching, the radiation-induced loss of pre-irradiation optical fiber can be
reduced effectively. The obtain results also have been analyzed in detail.
Infrared spectra of optical fiber cladding materials have been investigated by the irradiating treatment, and the
quenching and annealing process with different temperature. The results show that, with the method of quenching firstly,
the 1100 cm-1 peak in the IR spectrum of cladding materials changes dramatically, which may attribute to the quenching
process, corrected the fictive temperature and induced structural disorder. And then, the irradiation process induces
defects. Finally annealing process can make the material become more stable, but the intensity and shape of 1100 cm-1
peak no change remarkably. This result shows that annealing process repaired the structural disorder induced by
quenching process and the defects induced by irradiated.
Reducing the radiation-induced transmission loss in low water peak single mode fiber (LWP SMF) has been investigated
by using photo-bleaching method with 980nm pump light source and using thermal-bleaching method with temperature
control system. The results show that the radiation-induced loss of pre-irradiation optical fiber can be reduced effectively
with the help of photo-bleaching or thermal-bleaching. Although the effort of photo-bleaching is not as significant as
thermal-bleaching, by using photo-bleaching method, the loss of fiber caused by radiation-induced defects can be
reduced best up to 49% at 1310nm and 28% at 1550nm in low
pre-irradiation condition, the coating of the fiber are not
destroyed, and the rehabilitating time is just several hours, while self-annealing usually costs months' time. What's more,
the typical high power LASER for photo-bleaching can be 980nm pump Laser Diode, which is very accessible.
Defect centers play a major role in the radiation-induced transmission loss for silica optical fibers. We have investigated
characteristics of the best known defect centers E' in silica optical fiber material irradiated with γ ray at room temperature,
and measured by using electron spin resonance (ESR) and spectrophotometer. The results show that the defect
concentrations increase linearly with radiation doses from 1kGy to 50kGy. We have established the mechanism models
of radiation induced defect centers' formation. We have also studied the influences of thermal annealing on defect centers.
The radiation induced defect centers can be efficiently decreased by thermal annealing. Particularly, the defect
concentration is less than the initial one when the temperature of thermal annealing is over 500°C for our silica samples.
These phenomena can also be explained by the optical absorption spectra we have obtained.