Abstract

In recent years much work has been done to determine the cause of photosensitive grating effects in germanium-doped silica fibers. Past research has suggested a link between the formation of defect centers and the occurrence of photosensitivity in these materials. For the first time, we observe a correlation between photosensitivity and the Ge E' center, characterized by a singly charged oxygen vacancy, as measured with electron-spin resonance (ESR) techniques. We irradiated a length of single-mode optical fiber (n = 0.028, c = 438 nm) with argon laser radiation in the usual manner. A grating was written in the fiber, and optical transmission and reflection data were recorded. Subsequently, the fiber end was dipped in index-matching fluid, prohibiting back reflection, and the sample was re-exposed with a high-power Ar⁺ laser beam for an extended time to induce sufficient defects to be detectable with ESR. Analysis of optical data at a wavelength of 488 nm showed a 50% decrease in fiber transmission after 3.5 s. ESR analysis of the same sample showed the Ge E' defect concentration more than doubled over that of an identical, but unexposed, fiber. We will discuss the significance of these results in the context of the current theory of two-photon absorption to these E' centers.

© 1990 Optical Society of America