Dispersion relation of core odd mode, SPP mode and loss spectra of core odd mode for (a) X-polarization and (b) Y-polarization light. The insets show the distribution of modal electric field at the resonance wavelength. The loss of X-polarization odd mode is larger than that of Y-polarization odd mode. The structural parameters used for the calculations are d₁ = 0.8 μm, d₂ = 0.8 μm, Λ = 2.0 μm.