Formation and conversion of defect centers in low water peak single mode optical fiber induced by gamma rays irradiation

Abstract

The formation and conversion processes of defect centers in low water peak single mode optical (LWPSM) fiber irradiated with gamma rays were investigated at room temperature using electron spin resonance. Germanium electron center (GEC) and self-trapped hole center (STH) occur when the fibers are irradiated with 1 and 5 kGy cumulative doses, respectively. With the increase in irradiation doses, the GEC defect centers disappear, and new defect centers such as E′ centers (Si and Ge) and nonbridge oxygen hole centers (NBOHCs) generate. The generation of GEC and STH is attributed to the electron transfer, which is completely balanced. This is the main reason that radiation-induced attenuation (RIA) of the LWPSM fiber is only 10 dB/km at communication window. The new defect centers come from the conversion of GEC and STH to E′ centers and NBOHC, and the conversion processes cause bond cleavage, which is the root cause that the RIA of the LWPSM fiber significantly increases up to 180 dB/km at working window. Furthermore, the concentration of new defect centers is saturated easily even by increasing cumulative doses.

Influence of Irradiation and Annealing on Structural Properties of the Optical Fiber Cladding Material

“…We think the Ge elements may diffuse into the cladding material during the optical fiber preform manufacturing. Then the GeE's are generated when Ge-O bonds breakage happen, while Ge(1) and Ge(2) centers are generated when radiation-induced electrons are transferred from bridging oxygen to a adjacent fourfold coordinated Ge ions [2]. Because Ge contained in fiber cladding materials is the minority from the limited amount of diffusion, Ge-related defect centers are not discussed here; instead, we mainly focus on the Si-O bond breaking process and breakage position.…”

“…Therefore, the ESR peak labeled is the result of the joint action of the SiE' and GeE' color centers. The signal labeled corresponds to the nonbridging oxygen hole center (NBOHC), characterized by g values: [2], [23]. The SiE' and NBOHC in the fiber material are mainly from the Si-O-Si bond breakage [2], [15], [24], [25] while the Ge-O-Si bond breaking produces the GeE' and NBOHCs [2].…”

“…3(a) and 3(b), it is obvious that defect centers completely disappear after annealing, which shows that high temperature thermal process can repair defects induced by irradiation. The Ge(1) and Ge(2) defects caused by Ge impurities are annealed too, because the GEC centers are thermally less stable [26], and at high temperature they also disappear [2], [28].…”

“…L OW water peak single-mode optical fiber (LWP SMF) has become widely used to extend the bandwidth of dense wavelength division multiplexing (DWDM) communication systems because the absorption effect of 1383 nm peak is greatly reduced [1], [2]. With the continuous extension of optical fiber applications in the radiation field, radiation property of fiber has attracted much research attention [3]- [6].…”

“…Since R. A. Weeks [8] first reported the center in Manuscript 1956, many groups [2], [9]- [15] analyzed its characteristics. Generally, formation of E' color center is attributed to the bond breakage of oxygen deficiency centers [11]- [13], the Si-O bond breaking [2], [14], [15], and some other precursors changes under radiation conditions.…”