Year: 2007
Vladimír Kuzmiak, Ph.D.
We studied dielectric layers characterized by gradient dielectric function which leads to a non-local dispersion with a cutoff frequency that separates frequency ranges supporting traveling and evanescent waves. For realistic values of the modulation of the refractive index the system supports evanescent s-waves while for p-waves predicts traveling regime, i.e. in contrast to photonic barrier with a homogeneous profile the tunneling becomes polarization-depentent. By using exactly solvable model we examined the effect of concave profile that characterizes photonic barrier on the reflectance and transmittance of a single and double layer for both s- and p-wave incidenting with arbitrary angle. We have shown that by increasing of the modulation depth of the refractive index our model predicts in the regime of reflectionless tunneling the existence of the transmittance peaks for s-waves – see Fig. 1.We proved that unlike in the case of the square barrier with constant refraction index the cancellation of the reflected wave occurs due to the interference between the reflected wave and transmitted part of the evanescent wave at the interface between the gradient layer and vacuum. The effect of nonattenuated tunneling is analogous to the superlensing phenomenon in which evanescent waves contribute to the perfect image of the objects by means of negative refractive index medium and represent an alternative concept of energy transfer that employs evanescent waves and may be useful in design of subwavelength devices. Using different profiles opens a possibility of design of new class of metamaterials in which spatial distribution implies resonant behavior of the permittivity that is in contrast to metallic negative index medium not accompanied with a sizable absorption.
Transmittance of both gradient and homogeneous single layer (n0 = 1.4) for inclined incidence of s- (full line) and p- waves (dotted line) vs. frequency dependent parameter γ(u) with modulation depth m = 0.75 and angle of incidence θ = 65°. Transmittances of the homogeneous layers for s- and p-waves are denoted as shmg and phmg, respectively.
