Abstract

In the last few years, there has been a tremendous growth in uv-exposed grating-based devices. The use of hydrogen-loading¹ to sensitize fibers has resulted in index changes as high as 10'². Two predominant fabrication methods include the holographic interference of two beams² and the use of phase masks³. While extremely efficient gratings have been fabricated, the increase in birefringence of the fiber device during the writing process is not completely understood. The evaluation of the cause of this birefringence is critical to the design and analysis of grating-based resonant devices such as stable fiber lasers⁴ and laser-based polarimetric heterodyned sensors.⁵ Two plausible explanations have been put forth in the past to explain this phenomenon. It has been shown® that birefringence is dependent on the polarization of the writing beam and that uv-light polarized along the fiber propagation axis results in reduced birefringence.⁷ Additionally, the geometrical asymmetry of the writing process has been considered to be a possible cause but no proof of corroboration or contradiction has been put forth. In this paper, we provide concrete evidence demonstrating the geometrical asymmetry as a major cause of the birefringence. Further, we also show that a double-sided exposure of the fiber reduces the birefringence independent of the polarization of the writing beam.

© 1994 Optical Society of America