Spun-Related Effects on Optical Properties of Spun Silica Optical Fibers

Spun-related effects on optical properties of silica optical fibers have been investigated experimentally. In addition to the previously known spun effects on polarization mode dispersion (PMD), we observed previously unknown spun-related effects on mode field diameter (MFD), cutoff wavelength and Verdet constant. These effects are significant at highly spun (short pitch length) fibers which are draw at high rotation rate and low drawing speed. By fabricating and testing spun fibers of varying pitch lengths, we found that MFD, cutoff wavelength and PMD all decrease as the pitch length decreases, while the fiber loss increases significantly when the pitch length is lower than 1.5 mm. We have also investigated the spun and annealing effects on Verdet constant of spun fibers. Our experimental results reveal that, by increasing the spun rate (i.e., decreasing the spun pitch length), the Verdet constant is increased appreciably. One relevant finding is that the increase of Verdet constant of spun fibers after annealing is inversely proportional to the pitch length. The overall Verdet constant increase, due to spun and annealing processes, can reach about 4.5% at 1550 nm wavelength in a spun fiber with 1.0 mm pitch.