Refractive-index changes of titanium-doped near-stoichiometric LiNbO3 crystals

Titanium-doped (up to 9 mol%) near-stoichiometric LiNbO3 (SLN) crystals were grown from lithium-rich solutions by the top-seeded solution-growth method. The ordinary and the extraordinary refractive indices (n(o) and n(e)) of the titanium-doped SLN (Ti:SLN) crystals were measured at room temperature by the prism-coupling technique in the wavelength range from 440 to 1550 rim. The relations between titanium concentrations and the ordinary and the extraordinary refractive-index changes (Deltan(o) and Deltan(e)) of the Ti:SLN crystals were investigated. Accordingly, it was found that both Deltan(o) and Deltan(e) linearly increase with increasing titanium concentration up to 9 mol% and that Deltan(e) is much larger than Deltan(o) over the whole wavelength range. It was also found that both Deltan(o) and Deltan(e) increase with decreasing wavelength in all the Ti:SLN crystals with different titanium concentrations. Moreover, Deltan(e) of Ti:SLN doped with approximately 4 mol% of titanium (approximately 1 x 10(-2)) is almost the same as that of titanium-diffused SLN waveguides. In addition, a photoelastic effect on the refractive-index changes in the Ti:SLN crystal was estimated from using lattice-constant data determined by X-ray diffraction.