Conventional optical modes are supported by the total internal reflection occurring due to refractive index difference. Surface modes guided through an interface seem to have a different origin from them because they are supported by the difference in the signs of constitutive parameters of two media comprising the interface. Here, we propose that these surface modes have their origin in the accumulated polarization charges (or magnetization currents) near the interface. To induce such an accumulation, we need to make the normal component of the electric field (or the tangential component of magnetic flux density) on each side of the interface mutually antiphase, which entails different signs of constitutive parameters across the interface.
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