Controlling the flow of light is fundamental to optical applications. With the recent advances in nanofabrication capabilities and new theoretical concepts, ground breaking platforms for the nanoscale manipulation of light have been demonstrated in recent years. These include metasurface and epsilon-near-zero (ENZ) materials and structures, which offer unique optical features such as sub-wavelength field confinement, unusual optical nonlinear/quantum properties and advanced wavefront shaping.
This talk will review our recent development on an electrically tunable conducting oxide metasurface that can tune the optical phase and amplitude and a broadband, tunable, and ultrathin conducting oxide epsilon-near-zero for meta-devices. I will present our recent development on the use of gate-tunable materials, transparent conducting oxides, to demonstrate an electrically tunable metasurfaces that can tune the optical phase and amplitude for ultrathin beam steering devices . In addition, a broadband, field-effect tunable, and ultrathin ENZ perfect absorber enabled by the excitation of ENZ modes will be discussed [2,3].
1. Y. W. Huang, H. W. Lee, R. Sokhoyan, R. Pala, K. Thyagarajan, S. Han, D. P. Tsai, and H. A. Atwater, “Gate-tunable conducting oxide metasurfaces,” Nano Lett. 16, 5319-5325 (2016).
2. A. Anopchenko, L. Tao, C. Arndt, H. W. Lee, “Gate tunable and broadband Epsilon-near-zero perfect absorbers with deep subwavelength thickness,” ACS Photonics (accepted, 2018).
3. A. Anopchenko, S. Gurung, L. Tao, C. Arndt, H. W. Lee, “Atomic Layer Deposition of Ultra-thin and smooth Al-doped ZnO for Zero-Index Photonics”, Materials Research Express, 5, 014012 (2018).
Metasurfaces that can refract and focus light in unique ways provide the opportunity for advanced light manipulation and development of novel applications. Due to the flat nature of metasurfaces (typical thickness < 100nm), conventional three-dimensional optical elements such as prisms or lenses could be replaced by flat, low-profile, and low-cost versions. In addition, the optical response of near-zero refractive index metasurface systems, i.e., vanishing permittivity and permeability values, have been shown to exhibit unique optical properties. Those features can be exploited in various optical applications such as wavefront engineering, radiation pattern tailoring, non-reciprocal magneto-optical effects, nonlinear ultrafast optical switching, and broadband perfect absorption. However, most of the studies on epsilon-near-zero (ENZ) optical properties are limited to the excitation of ENZ mode in the planar structures or meta-surfaces with short interaction length, restricting the excitation platform for novel optical device applications.
In this talk, I will report a novel optical waveguide design of a hollow step index fiber modified with a thin layer of conducting oxide epsilon-near-zero materials. We show an excitation of highly confined waveguide mode in the proposed fiber near the wavelength where permittivity of conducting oxide material approaches zero . I will present our study on “meta”-optical fiber by integrating metasurfaces with optical fibers to develop novel and ultracompact in-fiber optical devices such as an optical fiber metalens and color filter [2,3]. These advanced “meta”/ENZ-optical fibers open the path to revolutionary in-fiber optical imaging and communication devices.
1. K. Minn, A. Anopchenko, J. Yang, H. W. Lee, “Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber,” Nature Scientific Reports 8, 2342 (2018).
2. J. Yang, I Ghirmire, P. C. Wu, S. Gurung, C. Arndt, D. P. Tsai, H. W. Lee, “Photonic crystal fiber metalens”, submitted (2018).
3. Indra Ghimire, Jingyi Yang, Sudip Gurung, Satyendra K. Mishra and Ho Wai Howard Lee,” Polarization dependent photonic crystal fiber color filter using asymmetric metasurfaces,” Submitted (2018)