Multidimensional multiplexing geometric phase metaholography

Meta-holograms, the computer-generated holograms assisted with nano-structured metasurfaces, promise efficient recording of light at the nanoscale. Adopting the multiplexing principle further bestows meta-holography with superb capacity for information storage and imaging applications. However, conventional meta-holograms mostly employ a single physical dimension to multiplex the holograms with incomplete light modulation, which imposes critical limitations on holography fidelity.

 

In a new paper published in Light: Advanced Manufacturing, a team of scientists, led by Professor Jian Wang and Jinwei Zeng from Wuhan National Laboratory for Optoelectronics and School of Optical and Electronic Information, Huazhong University of Science and Technology, China, and co-workers, have developed a method for multi-dimensional holographic multiplexing and encryption using full-modulation dielectric geometric-phase metasurfaces. Such metasurfaces enable simultaneous, independent, and arbitrary control of the amplitude, phase, and polarization of spatial light based on the geometric-phase principle, with broadband properties. Based on the full-modulation principle, the metasurfaces enable the meta-holograms to multiplex multiple holographic images with engineered patterns, polarizations, and directions, depending on the particular input and output conditions. Compared with the holograms acquired with incomplete light modulation, the designed meta-holograms not only inspire an accurate high-capacity information integration with low crosstalk and ideal energy uniformity, but can also facilitate complex multi-dimensional optical information broadcasting, anti-counterfeit, and encryption in compact optoelectronic devices.

 

The broadband full-modulation metasurface is accomplished by the parallel tasking method based on the geometric-phase principle. Specifically, the geometric-phase principle describes the relation between the phase shift of the transmitted light in the orthogonal polarization component and the in-plane orientation angle of an anisotropic element. On this basis, the supercell with 2×2 unitcells (anisotropic elements) is introduced as the fundamental building block of the metasurface. Furthermore, the rotating angle of each unitcell is divided into three sub-angles. Each of these sub-angles serves as an independent control factor to respectively manipulate light’s phase, amplitude, and polarization through geometric phase, interference, and orthogonal polarization superposition. Crucially, since the phase, amplitude, and polarization profiles solely depend on the rotation angle of each unit cell, the group of supercells leads to full-modulation metasurfaces that can work in a broadband with high robustness. Furthermore, this metasurface leverages the full Stokes polarization and transverse momentum dimensions to multiplex multiple holographic images with deliberated information encryption. These scientists gave a general demonstration:

 

“A pre-designed fabricated metasurface encodes the intended multiplexing information, manifested as the holographic images of 6 letters “H, S, A, B, U, T”. Depending on the specific reading conditions (i.e., the incident/transmitted polarizations and directions, etc.), the metasurface selectively exhibits the corresponding images within the designated channels.”

 

“We emphasize that such a concept only illustrates rather simple schematics for presentation convenience. In principle, these conditions can be expanded to accommodate many more input/output directions or employ other multiplexing dimensions. Considering the enormous possible combinations of input/output conditions, the proposed meta-holography can support a very sophisticated holography multiplexing/demultiplexing strategy,” they added.

 

“Leveraging this full-modulation capability, our proposed meta-holograms feature the capability of more accurate and versatile image construction. This advancement is crucial for future applications in optical information storage, broadcasting, and encryption, promising significant enhancements in communication capacity and confidentiality through multi-dimensional concealment of genuine information.” the scientists forecast.

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