Anomalous attenuation and depolarization scattering in y-cut LiNbO3proton exchanged waveguides

A large anomalous attenuation and depolarization scattering have been observed in
y
-cut,
x
-direction propagating LiNbO
3
proton exchanged waveguides at 0.632 μm wavelength. We observe this phenomenon only when the mode effective index is smaller than the ordinary index
n_{0} (n_{0} = 2.286)
. The effect is caused by phase-match scattering into the substrate. Exchange solutions with various mole percentages of lithium benzoate have been used and the same phenomenon has been consistently observed.