Coherent Control of Surface Plasmon Polaritons in Anisotropic Medium

We theoretically investigate the coherent control of anisotropic surface plasmon polaritons (SPPs) in an anisotropic medium. The transverse electric and transverse magnetic reflection and transmission coefficients, dispersion relations, wavelengths, and propagation lengths of the SPPs are analyzed under the influence of a coherent field. The perpendicular component of the dielectric tensor incorporates a three-level Λ-type atomic configuration. The dispersion along the x and y axes can be tuned by adjusting the control field, probe-field detuning, and the optical axis orientation ϕ. The SPP wavelength along both directions remains in the sub-wavelength regime for almost all control field values and optical orientation angles, except at ϕ=40∘, where the wavelength along the y direction slightly exceeds the incident wavelength. A maximum propagation length of 270 μm along the x direction is observed for ϕ=30∘ and a control field Ωc=2γ (with all other parameters scaled to γ), which is nearly five times longer than the propagation distance along the y direction, indicating lower energy losses along the horizontal direction. These results enable precise spatial manipulation of SPPs and may be leveraged in the development of active plasmonic components such as tunable directional waveguides, reconfigurable optical switches, and anisotropic metasurfaces for polarization-sensitive signal processing.