CORRELATION OF REFRACTIVE-INDEX PROFILES WITH SUBSTITUTIONAL HYDROGEN CONCENTRATIONS IN ANNEALED PROTON-EXCHANGED LINBO3 WAVE-GUIDES

We have studied the behavior of the extraordinary refractive index in a set of annealed z-cut proton-exchanged lithium niobate (LiNbO3) substrates by means of optical prism-coupling measurements and numerical simulations. Values of the index as a function of depth have been determined and fitted with a single Gaussian diffusion expression. At 400-degrees-C, the effective index diffusivity D(n) of 4.6 x 10(-12) cm-2/s is nearly identical to the diffusivity of substitutional H in these samples. Furthermore, we find a linear relationship between the increase in the extraordinary refractive index and the substitutional H concentration. At a wavelength of 0.6238 mum, the coefficient for this relationship is approximately 1.5 X 10(-23) (H cm-3)-1.