Abstract
Metasurfaces have enabled the realization of several optical functionalities over an ultrathin platform, fostering the exciting field of flat optics. Traditional metasurfaces are achieved by arranging a layout of static meta-atoms to imprint a desired operation on the impinging wavefront, but their functionality cannot be altered. Reconfigurability and programmability of metasurfaces are the next important step to broaden their impact, adding customized on-demand functionality in which each meta-atom can be individually reprogrammed. We demonstrate a mechanical metasurface platform with controllable rotation at the meta-atom level, which can implement continuous Pancharatnam–Berry phase control of circularly polarized microwaves. As the proof-of-concept experiments, we demonstrate metalensing, focused vortex beam generation, and holographic imaging in the same metasurface template, exhibiting versatility and superior performance. Such dynamic control of electromagnetic waves using a single, low-cost metasurface paves an avenue towards practical applications, driving the field of reprogrammable intelligent metasurfaces for a variety of applications.
Highlights
Xu et al.: Mechanically reprogrammable Pancharatnam–Berry metasurface for microwaves most importantly techniques for tunable/reprogrammable metasurfaces that can be flexibly controlled on demand and in real time.[25,26,27]
Digital and real-time features promote several system-level applications that can hardly be achieved by static metasurfaces, such as space-time-coding,[42,44,54] intelligent autonomous self-adaptive systems,[40,45,46] and dynamic optimization of wireless communication channels.[47,49,51]
Programmable metasurfaces utilizing varactor diodes can enable phase levels larger than four;[41,46,53] their operation was based on the dynamic phase around a resonance dip,[38] resulting in the significant amplitude variation when adjusting the phase response
Summary
As one of the most rapidly expanding frontiers of modern photonics, metasurfaces hold promise for a wide range of applications due to their compact physical size and unconventional (plasmonic or dielectric structures) with spatially varying geometrical parameters and subwavelength separations aimed at imprinting on the incoming optical wavefront a functionality[7,8,9,10,11,12] of choice through tailored local interactions of the phase,[13,14,15] amplitude,[16,17,18] and polarization.[19,20,21] The further development of this field entails endeavors to optimize the static metasurface performance for certain functionalities[22,23,24] andAdvanced PhotonicsDownloaded From: https://www.spiedigitallibrary.org/journals/Advanced-Photonics on 07 Feb 2022 Terms of Use: https://www.spiedigitallibrary.org/terms-of-useJan∕Feb 2022 Vol 4(1)Xu et al.: Mechanically reprogrammable Pancharatnam–Berry metasurface for microwaves most importantly techniques for tunable/reprogrammable metasurfaces that can be flexibly controlled on demand and in real time.[25,26,27] In the terahertz and optical regimes, dynamic metasurfaces have mainly been achieved by utilizing the response of tunable materials to external stimuli, such as optical pump,[28,29,30,31] heating,[32,33,34] and bias voltage.[35,36,37,38] limited by the current techniques of fabrication and modulation, these metasurfaces have been limited to simultaneous tuning of a large portion of the meta-atoms, and can only be switched among a limited number of operations.In the microwave regime, PIN diodes and varactor diodes have been recently used to design reprogrammable metasurfaces with individually reconfigured meta-atoms,[39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54] due to their miniaturized sizes compatible with passive metallic resonators. It limits the amount of information that can be processed by a metasurface of given size.[55] Programmable metasurfaces utilizing varactor diodes can enable phase levels larger than four;[41,46,53] their operation was based on the dynamic phase around a resonance dip,[38] resulting in the significant amplitude variation when adjusting the phase response To eliminate such amplitude-phase correlation-induced distortion in specific wavefront control, due consideration should be paid into inverse design optimization algorithms.[56,57] each meta-atom in electrically or optically reprogrammable metasurfaces requires at least one PIN diode, photodiode, or varactor diode,[39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54] whose typical power dissipation is about several hundred milliwatts, and they need a continuous power supply to maintain the functionality. Such energy consumption entails a trade-off between the size/number of meta-atoms and the overall metasurface size, hindering large-scale applications
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