Epsilon-near-zero (ENZ) metamaterials have been studied in various research areas such as wavefront engineering, supercoupling effect, strong coupling, nonlinear optics, and perfect absorption. An ideal ENZ material of ε=0 is highly omnireflective at any angle of incidence. For a real ENZ material of Re(ε)≈0 the imaginary part Im(ε) is not zero from the causality principle. At an ENZ wavelength at Re(ε)≈0, the normal electric field (E_z ) in an ENZ thin film with a very small Im(ε) becomes very strong and the group velocity slows down; E_z is inversely proportional to the thickness of the film and the imaginary part of ε, resulting in a large light absorption in a low optical loss ENZ thin film. We investigate the tunable ENZ wavelength of indium tin oxide (ITO) thin films in the NIR wavelength regime which are controlled by the film growth conditions and demonstrate the broadband perfect absorption (PA) using the ITO multilayers of different ENZ wavelengths.
Coherent perfect absorption (CPA) is an optical phenomenon occurring in an absorbing thin film by the interaction of two counter-propagating coherent waves. We propose a new broadband CPA scheme based on ENZ multilayer films and investigate the multi-wavelength optical switching, indicating that the on- and off-states can be controlled by the phase shift and wavelength of the two incident waves.
In this lecture we provide design principles and fabrication guidelines for thin film ENZ devices for PA and CPA, which can find various applications in optical switches, modulators, filters, sensors, and energy harvesting devices.
Chang Kwon Hwangbo, "Broadband perfect absorption of epsilon-near-zero thin films (Conference Presentation)," Proc. SPIE 10356, Nanostructured Thin Films X, 103560A (Presented at SPIE Nanoscience + Engineering: August 10, 2017; Published: 3 October 2017); https://doi.org/10.1117/12.2272541.5597185658001.
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