Figure 3. The normalized wavenumber Re(β)/k₀ of the anti-symmetric coupled SPPs (a) as a function of the thickness d₄ of the PR layer and (b) as a function of the dielectric constant ε₄ of the PR layer.

The operating wavelength λ₀ ( = 2π/k₀) is fixed at 193 nm. The dielectric constant ε₄ of the PR layer is 2.89 in (a). The thickness d₄ of the PR layer is 25 nm in (b).