Abstract

The achievement of high conversion efficiencies for second-harmonic generation (SHG) in germania-doped optical fibers requires an understanding of the material properties of the fiber as well as the saturation mechanisms limiting the growth of the (2) grating. In this paper we report material modification of germania doped fibers by gamma rays irradiation that allows previously un-conditionable fibers to be conditioned for SHG. We also observed significant enhancement in the efficiency and preparation rate of previously conditionable fibers. In the context of our previously developed rate equation model for the evolution of (2) gratings,¹ these results suggest an enhancement of the number density of defects participating in the self-organization process. We investigated the nature of these defects and the role of oxygen vacancies in the germanosilicate matrix in the self-organization process by use of high-energy radiation, which can produce oxygen vacancies,² as well as low energy radiation that is incapable of producing any vacancies. We also present results of a Raman study of gamma-irradiated fibers. New insights into the preform preparation environment and fiber drawing conditions, suitable for writing of self-organized (2), gratings, are gained from these studies.

© 1990 Optical Society of America