Abstract
Amplitude–phase spectra of IR waves tunneling through a gradient dielectric nanophotonic barrier, found in the framework of an exactly solvable model of this medium, are used for optimization of superluminal reshaping of tunneling pulses. This barrier, characterized by a cut-off frequency Ω, determined by the shape of distribution of refractive index across the barrier, provides the tunneling regime for waves whose frequencies are less than Ω. In a spectral range, located nearby this cut-off frequency Ω, an almost reflectionless tunneling of these waves occurs, accompanied by large strongly dispersive phase shifts. These shifts outstrip in some spectral range the phase shifts accumulated by the same harmonics along the same way in free space. Depending on the detuning between the pulse carrier frequency and Ω, the interplay between superluminal (tunneling) and subluminal (transparent) harmonics results in an ultrafast reshaping of the transmitted waveform, yielding a pulse spatial broadening, formation of superluminal precursors at the front edge of the transmitted pulse, and the splitting of the pulse’s maximum, while the displacement of the center of gravity of reshaped pulse stays subluminal.
© 2011 Optical Society of America
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