Abstract
A wavelength de-multiplexing metasurface hologram composed of subwavelength metallic antennas is designed and demonstrated experimentally in the terahertz (THz) regime. Different character patterns are generated at the separated working frequencies 0.50 THz and 0.63 THz which determine a narrow frequency bandwidth of 130 GHz. The two working frequencies are around the central resonance frequency of the antennas where antennas behave strong wavefront modulation. Each antenna is fully utilized to control the wavefront of the metasurface at different frequencies by an optimization algorithm. The results demonstrate a candidate way to design multi-colors optical display elements.
Highlights
IntroductionWhen the device is illuminated with desired multi-wavelength light, the light with different frequency will be modulated by each antenna
The pattern generated by different frequency can overlap with each other, a colorful image can be generated on the preset plane
The dual-color THz metasurface hologram is designed by the simulated annealing (SA) algorithm and fabricated by the ultraviolet lithography
Summary
When the device is illuminated with desired multi-wavelength light, the light with different frequency will be modulated by each antenna. The pattern generated by different frequency can overlap with each other, a colorful image can be generated on the preset plane. Each antenna contributs to the wavefront modulation of metasurface at the preset working frequencies. When the metasurface is illuminated by the linearly polarized plane wave from the substrate side, the image can be reconstructed by the transmitted cross-polarized light. Two character images overlap at the observation plane for their working frequency simultaneously. The same C-shaped subwavelength metallic antennas proposed by Zhang et al in the THz regime[18], as shown, are adopted as dual-color wavefront modulator units. It’s better to consider both amplitude and phase modulation of the hologram for achieving a good reconstruction quality
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