Tunneling of electromagnetic waves: paradoxes and prospects

Electromagnetic wave tunneling through photonic barriers and effects of frustrated total internal reflection (FTIR) are considered for waves of different spectral regions. The discovered effects of nonlocal dispersion of gradient dielectric barriers, wherein the spatial permittivity profile $\varepsilon(z)$ determines the cutoff frequency that depends on the shape and geometric parameters of this profile are shown to play the decisive role in wave tunneling through nonuniform barriers. Special emphasis is placed on the effects of total wave transmission at frequencies lower than the cutoff frequency in the FTIR mode (reflection-free tunneling) characteristic of gradient media. The generality of these effects for а broad wave spectrum is illustrated using exact analytic solutions of the Maxwell equations describing wave tunneling through nonuniform transparent dielectrics. Also discussed are controversial issues surrounding the FTIR theory and the prospects for using gradient photonic barriers for the development of thin-film filters and polarizers, efficient reflectors, and reflection-free coatings.