Abstract
A polarization independent holographic beam splitter that generates equal-intensity beams based on geometric metasurface is demonstrated. Although conventional geometric metasurfaces have the advantages of working over a broad frequency range and having intuitive design principles, geometric metasurfaces have the limitation that they only work for circular polarization. In this work, Fourier holography is used to overcome this limitation. A perfect overlap resulting from the origin-symmetry of the encoded image enables polarization independent operation of geometric metasurfaces. The designed metasurface beam splitter is experimentally demonstrated by using hydrogenated amorphous silicon, and the device performs consistent beam splitting regardless of incident polarizations as well as wavelengths. Our device can be applied to generate equal-intensity beams for entangled photon light sources in quantum optics, and the design approach provides a way to develop ultra-thin broadband polarization independent components for modern optics.
Highlights
A polarization independent holographic beam splitter that generates equal-intensity beams based on geometric metasurface is demonstrated
Conventional geometric metasurfaces have the advantages of working over a broad frequency range and having intuitive design principles, geometric metasurfaces have the limitation that they only work for circular polarization
Conventional beam splitters based on the Geometric metasurfaces (GEMs) has been designed by linear phase gradient which leads to separation depending on the circular polarization direction[31,32,34]
Summary
A polarization independent holographic beam splitter that generates equal-intensity beams based on geometric metasurface is demonstrated. Geometric metasurfaces (GEMs) that operate for the circular polarization have a broad range of working frequency because they generate phase delay by rotating the antennas, which is less resonant than the resonance tuning method. The Rochon prism which leaves ordinary ray undeviated can be realized by controlling both propagation and geometric phase of each unit structure[35], but its working frequency is strictly limited to a narrow band In modern optics such as quantum communication, equal-intensity coherent beams are usually required to generate entangled photon light sources[36,37,38,39]. The number of generated beams which have equal-intensity from our device is controllable Our device achieves both broadband characteristics and the polarization-independence by using Fourier holography on GEMs. The term of ‘broadband’ in this work does not mean consistent efficiency. Our device and design approach can be applied to interferometry in classical optics as well as generation of entangled photon light sources in quantum optics
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