Abstract
Conventional metasurface reflector-arrays based on metallic resonant nanoantenna to control the wavefront of light for focusing always suffer from strong ohmic loss at optical frequencies. Here, we overcome this challenge by constructing a non-resonant, hybrid dielectric-metal configuration consisting of TiO2 nanofins associated with an Ag reflector substrate that provides a broadband response and high polarization conversion efficiency in the visible range. A reflective flat lens based on this configuration shows an excellent focusing performance with the spot size close to the diffraction limit. Furthermore, by employing the superimposed phase distribution design to manipulate the wavefront of the reflected light, various functionalities, such as multifocal and achromatic focusing, are demonstrated for the flat lenses. Such a reflective flat lens will find various applications in visible light imaging and sensing systems.
Highlights
Conventional metasurface reflector-arrays based on metallic resonant nanoantenna to control the wavefront of light for focusing always suffer from strong ohmic loss at optical frequencies
We propose and numerically demonstrate that a non-resonant, hybrid dielectric-metal configuration consisting of dielectric nanofins associated with metallic mirror substrate can be used to build a metasurface element and work as a phase shifter for the desired phase profile
To achieve high polarization conversion efficiency which is required for effective manipulation of reflected light, the phase difference between the reflection of x and y-polarized components of the nanofin should be equal to π
Summary
Conventional metasurface reflector-arrays based on metallic resonant nanoantenna to control the wavefront of light for focusing always suffer from strong ohmic loss at optical frequencies We overcome this challenge by constructing a non-resonant, hybrid dielectric-metal configuration consisting of TiO2 nanofins associated with an Ag reflector substrate that provides a broadband response and high polarization conversion efficiency in the visible range. By employing the superimposed phase distribution design to manipulate the wavefront of the reflected light, various functionalities, such as multifocal and achromatic focusing, are demonstrated for the flat lenses. The hybrid structure exhibits a broadband (590~720 nm) optical response and high polarization conversion efficiency (higher than 80%) Based on this geometry, a reflective flat lens is designed in visible range, which is capable of focusing energy at arbitrary position above the metasurface though tuning phase profile formed by reflector-arrays. By designing a meta-molecule comprising two sets of different nanofins, the reflective flat lens is able to achieve various optical functionalities including multifocal and achromatic focusing
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