Abstract
We propose a general, easy-to-implement scheme for broadband coherent perfect absorption (CPA) using epsilon-near-zero (ENZ) multilayer films. Specifically, we employ indium tin oxide (ITO) as a tunable ENZ material, and theoretically investigate CPA in the near-infrared region. We first derive general CPA conditions using the scattering matrix and the admittance matching methods. Then, by combining these two methods, we extract analytic expressions for all relevant parameters for CPA. Based on this theoretical framework, we proceed to study ENZ CPA in a single layer ITO film and apply it to all-optical switching. Finally, using an ITO multilayer of different ENZ wavelengths, we implement broadband ENZ CPA structures and investigate multi-wavelength all-optical switching in the technologically important telecommunication window. In our design, the admittance matching diagram was employed to graphically extract not only the structural parameters (the film thicknesses and incident angles), but also the input beam parameters (the irradiance ratio and phase difference between two input beams). We find that the multi-wavelength all-optical switching in our broadband ENZ CPA system can be fully controlled by the phase difference between two input beams. The simple but general design principles and analyses in this work can be widely used in various thin-film devices.
Highlights
We propose a new broadband coherent perfect absorption (CPA) scheme based on epsilon-near-zero (ENZ) multilayer films
The ENZ wavelengths of indium tin oxide (ITO) films depend on doping levels that can be controlled during the film growth, and tunable perfect absorption could be achieved without any structural patterning
We show that the broad ENZ wavelength band in the effective dielectric constant of the ITO multilayer film is important in achieving broadband CPA
Summary
Switching Based on Epsilon-Near- received: 07 January 2016 accepted: 23 February 2016. By combining these two methods, we extract analytic expressions for all relevant parameters for CPA Based on this theoretical framework, we proceed to study ENZ CPA in a single layer ITO film and apply it to all-optical switching. In our previous theoretical and experimental works, we used ITO as a near-infrared (near-IR) ENZ material, and demonstrated perfect absorption in an ultra-thin ITO film In these works, an ITO film was coated on a reflective substrate (or we worked in the attenuated total reflection condition) in order to suppress the transmission. We use an ITO thin film as an ENZ layer, and find broadband CPA conditions in the near-IR region We use this broadband ENZ CPA for multi-wavelength all-optical switching in the telecommunication window. The design principles and analyses used here can be widely applied to various nanophotonic devices and components, such as optical switches, modulators, filters, sensors, and thermal emitters
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