Digital coding metasurface is aimed at building up a bridge between physics and information science. Higher information capacity of the digital coding metasurface means more powerful ability to control electromagnetic waves. Here, a multiband digital coding metasurface to improve the information capacity is proposed. The digital coding structures can provide 2‐bit digital states at three separate frequency bands (C, X, and Ku). It is shown that the proposed metasurface can eliminate the in‐band interference and path degradation by introducing an operator of frequency‐hopping spread spectra, from which flexible beam controls can be designed independently in every operating band. To demonstrate the capability and the compatibility, a multifunctional digital coding metasurface which can perform optical illusion, scattering reduction, and generation of orbital angular momentum in a shared aperture is presented. Numerical simulations and measured results have very good agreements, verifying excellent performance of the multiband digital coding metasurface. The proposed method opens opportunities to improve the information capacity of the digital coding metasurface and paves novel ways to multitasking systems on photonic applications.
In this paper, a dual-band reflective meta-hologram is designed providing two distinct information channels whose field intensity distributions can be independently manipulated at the same time. The proposed pure-phase meta-hologram is composed of several frequency-dispersive coding meta-atoms possessing each of 2-bit digital statuses of “00”, “01”, “10”, and “11” at either the lower (X-band) or the higher (Ku-band) frequency band. Relying on the weighted Gerchberg-Saxton phase retrieval algorithm, different illustrative examples have been provided to theoretically inspect the dual-band performance of our coding meta-hologram. Numerical simulations validate the proposed frequency multiplexing meta-holography with the ability to project two different high-quality images with low cross-talk on two X-band and Ku-band near-field channels located at distinct pre-determined distances from the metasurface plane. As proof of concept, two meta-hologram samples are fabricated, and the experimental results corroborate well the numerical simulations and theoretical predictions. The designed meta-hologram features all fascinating advantages of the coding metasurfaces while its performance overcomes that of previous studies due to providing two information channels rather than the conventional single-channel holography. The frequency multiplexing acquired by the proposed bi-spectral coding meta-hologram may provide great opportunities in a variety of applications, such as data storage and information processing.
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