Notice of Retraction: Excitation direction effect on polarization property of Er³⁺ electronic transition in LiNbO₃ waveguide and bulk material

We report that the polarization property of Er³⁺ transition in LiNbO₃ waveguide or bulk material is closely related to the incident direction of excitation beam relative to the optical axis of the crystal. It is found that the 1.5-μm transition is highly σ-(π-) polarized as the excitation direction is perpendicular (parallel) to the optical axis, and the 0.67-μ m transition reveals a reversed effect. Incident perpendicularly (parallel), the transition is highly π-(σ-) polarized. The effect is found to be independent of the polarization state and wavelength of the excitation light. It is attributed to the selective Er site excitation.