| Summary: | 碩士 === 國立中央大學 === 光電科學與工程學系 === 102 === Radiation-mode-enabled resonant optical tunneling in asymmetric, single barrier potential system with metal is investigated. The system consists of BK7 glass/silver (Ag)/titanium dioxide (TiO2)/air with the silver as the tunnel barrier. High transmittance (up to >70%) is shown to occur with transverse-electric wave incidence at near critical angle and a wavelength of 633 nm. Using finite-element-method-based simulation shows that the high transmittance - is -due to the excitation of a radiation mode of the geometry. Unlike ordinary resonator, the transmittance peaks at 328.2 and 473.9 THz in the frequency spectrum and decreases toward lower and higher frequencies. At lower frequencies, the reflectance at Ag-TiO2 interface decreases as the frequency is decreased which, from the Fabry-Perot model, weakens the resonance and leads to a lower transmittance. The decrease in transmittance as the frequency is increased is due to a low transmittance through the Ag layer , which reduces the field amplitudes penetrating into the TiO2 cavity. In the anology of quantum mechanics, the barrier thickness (normalized to wavelength) increases with the increasing frequency, which lowers the tunneling probability (i.e. transmittance) for a particle to penetrate into the cavity. On the other hand, decreasing frequency causes thinner normalized barrier thickness which would lower the confinement capability on the tunnel barrier side and increase the reflection probability back to the incident region. Experimental demonstration is pursued but to no avail due largely to sample preparations that require a small fabrication tolerance of <±1.7 nm.
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