We propose an ultrathin, high-performance quarter waveplate with extreme bandwidth in the near-to-mid infrared wavelength range based on a metasurface consisted of Ag fence-type gratings. The broadband quarter waveplate is realized by optimizing the anisotropic response of the metasurface via changing the geometric dimensions of the fence-type gratings to tailor the interference of light at the subwavelength scale. The near-constant phase difference between two perpendicular electric fields within the broad bandwidth is achieved by manipulating the dimensions of the fence-type gratings along two perpendicular directions in which localized plasmonic resonances along the two directions dominate. Compared to previously reported metasurface-enabled waveplates, the phase retardation of the electric components of the transmitted wave of the proposed structure can be fixed at ~π/2 across a broad wavelength range rather than merely limited within a narrow bandwidth near the resonant wavelength of the metasurface building blocks. Simulation results indicate that a function of quarter waveplates can be realized from 2000nm to 4500nm with the control of polarization orientation of a linearly polarized incident light. Our work gives intriguing possibilities for novel metasurface-enabled optical components with broad bandwidth for photonics devices.
In this paper, we report that normal incidence transmission of different circularly polarized waves through the 2D Archimedes’ nanoscale spirals is asymmetric. The structures consist of raised spiral ridge and two layers metal film covered on the substrate and the ridge. The finite difference time domain method was used to design the structure and perform the simulation. The device can distinguish the different circularly polarized wave across the transmission intensity compare with the common Archimedes’ nanoscale spirals which just exhibit the bright or dark modes in the light field. We confirmed that the device provide about 10% circular dichroism in 3.85um-6.0um broadband region. The circular dichroism in the wavelength 3.95 um can reach 13%. This ultracompact device could prove useful for remote sensing and advanced telecommunication applications.
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