Wavelength dispersion of Ti induced refractive index change in LiNbO3as a function of diffusion parameters

Z
-cut
X
-propagating, LiNbO
3
:Ti planar waveguides have been characterized over a wide range of diffusion conditions. Measurements of Ti concentration and refractive indexes have revealed Gaussian profiles. Their dependence with diffusion conditions have been studied. The relation, established at several wavelengths (
\lambda = 0.6328 \mu
m, 1.1523 μm, 1.523 μm), between extraordinary and ordinary refractive index change
\Deltan_{e,0}(z)
and titanium concentration
C(z)
is found to be nonlinear and of the form:
\Deltan_{e,0}(z) = A_{e,0}(C_{0},\lambda) (C(z))^{\alpha_{e,0}}
While
\alpha_{e,0}
is a constant, the proportionality coefficient
A_{e,0}
depends not only on the wavelength λ, but also on the diffusion conditions, characterized by C
0
, the Ti surface concentration of the diffused guide. Such a nonlinearity of Ti diffusion in LiNbO
3
has been revealed thanks to a complete and wide range investigation on both indiffused Ti and index profiles.