Polarization and angle dependent subwavelength coupling and dramatic reflection enhancement/reduction from an ITO-LiNbO3 interface

摘要

Two-dimensional electron gases (2DEGs) were demonstrated in indium-tin-oxide (ITO)-coated lithium niobate (LN) slabs by monitoring the very first reflection (VFR). Being dictated by light-matter interaction within the half-a-wavelength range, two-fold enhancement of the VFR was observed at one incidence angle, while two-and-half-fold reduction was obtained at another angle, when illuminating a Z-cut ITO-LN slab with two laser beams at 532 nm from the same side. In terms of exponential gain coefficient, such VFR enhancement/reduction corresponds to a range from -7.416 x 10(4) cm(-1) to +4.68 x 10(4) cm(-1), three orders of magnitude higher than that expected from the conventional photorefractive (PR) theory. The nanometer-thick 2DEG and the coupling role played by the evanescent field of the surface plasmon polaritons (SPPs) impose a much looser coherency requirement for the interacting light beams, which was verified by the solid energy coupling observed while rotating the polarization state of one laser beam. As much as 18.4 mW of the side diffraction mode associated with the light track formed on the slab surface, which sheds some light on the dramatic coupling dynamics. All these findings above were far beyond the reach of conventional PR theory, yet well consistent with the physical picture of 2DEG-supported SPPs and their interactions at the ITO-LN interface, offering a good opportunity to conceive and design future photonic/electronic devices for optical modulators.