Radiation response behaviour of high phosphorous doped step-index multimode optical fibers under low dose gamma irradiation

The radiation response behaviour of high phosphorous doped step index multimode (SIMM) fibers of different P2O5 concentrations and core diameters has been investigated in comparison with Ge doped SIMM fiber at different transmission wavelengths under 60Co gamma irradiation with variation of dose rates from 1Rad/hr to 100Rad/hr. Radiation induced absorption curves of P doped fibres show two broad absorption peaks in the wavelength ranges 400-420nm & 500-560nm which arise due to phosphorous oxygen hole center defect. It has been observed that at 540nm & 560nm transmission wavelengths sensitivity shows strong dose rate dependence compared to that at 502nm wavelength but does not show any saturation behaviour. This reveals that P related defects do not anneal at room temperature and yield permanent change. The radiation sensitivity decreases with increasing transmission wavelengths from 502nm to 560nm with very low fading behaviour. The fiber containing 16mol% P2O5 with coreclad dimension of 42:125 micron has an excellent linear radiation response behaviour with sensitivity around 1.0dB/m/100Rad at 502nm wavelength as well as very low recovery and dose rate independence. This enables its practical application in fiber optics personal dosimeter for measurement of low dose gamma radiation.