Photo-Annealing Effects on Gamma Radiation Induced Attenuation in Erbium Doped Fibers and the Sources Using 532-nm and 976-nm Lasers

Two erbium doped fibers (EDFs) with different radiation sensitivities were used in the photo-annealing tests, and their photo-annealing efficiencies were compared by using 532-nm and 976-nm lasers. For both EDFs, the 532-nm laser with 10 mW showed better efficiency than 976-nm laser with 290 mW. The radiation induced attenuation (RIA) could nearly be diminished in the wavelength range from 900 nm to 1700 nm by the photo-annealing of 532-nm laser. The half-time of recovery was 5.6 seconds by using 532-nm laser, and was about 40 minutes by using 976-nm laser whose annealing rate was similar to that of purely thermal annealing at about 330°C. For γ-irradiation tests of superfluorescent fiber sources (SFSs) exposed to a dose rate of 129.2 krad/hr, the rate of output power loss could be reduced by the 976-nm pump laser, but the output power loss could not be recovered. A most radiation-tolerant case was an SFS with 2.8-meter EDF#1 co-pumped by both the 532 nm and the 976 nm lasers. The output power loss could be recovered with a rate of 0.009 dB/min.

I. Introduction

Erbium Doped Fibers (EDFs) have been widely employed for optical communication and sensing. The EDFs show good performance and stability except in radiation environments such as for nuclear reactor or space applications. The reason has been known that the performance of an EDF-based device would be severely degraded by the RIA [1]–[5]. The RIA includes optical absorption bands of the corresponding radiation induced defects. To decrease RIA, some methods have been reported to reduce the defects such as thermal annealing [6], [7], hydrogen pre-loading [8], [9], and photo-annealing [9]–[14]. For thermal annealing, it needs to take up to 300°C to decrease RIA. Such a high temperature could damage many other devices; therefore, this method could not be employed practically. The hydrogen pre-loading method needs a hermetic coating to avoid out-diffusion of hydrogen, and the fabrication process of a hermetic coating might be complicated. The photo-annealing method may provide a simple and practical way to reduce RIA of an EDF-based device.