Stress-dependent growth kinetics of ultraviolet-induced refractive index change and defect centers in highly Ge-doped SiO2 core fibers

The evolution of the index change of type-IIa gratings observed in 28 mol % Ge-SiO2 core fibers with 1.8 mu m core diameter under various strains was measured from the optical spectra, and the induced defects at high and low strains were studied with electron spin resonance. Data will be presented t o show that the index modulation (Delta n(mod)) of type-IIa gratings is lik ely associated with Ge E-' centers. (C) 1999 American Institute of Physics. [S0003-6951(99)04141-8].