Dynamic piezoelectric MEMS-based optical metasurfaces

Abstract

Optical metasurfaces (OMSs) have shown unprecedented capabilities for versatile wavefront manipulations at the subwavelength scale. However, most well-established OMSs are static, featuring well-defined optical responses determined by OMS configurations set during their fabrication, whereas dynamic OMS configurations investigated so far often exhibit specific limitations and reduced reconfigurability. Here, by combining a thin-film piezoelectric microelectromechanical system (MEMS) with a gap-surface plasmon–based OMS, we develop an electrically driven dynamic MEMS-OMS platform that offers controllable phase and amplitude modulation of the reflected light by finely actuating the MEMS mirror. Using this platform, we demonstrate MEMS-OMS components for polarization-independent beam steering and two-dimensional (2D) focusing with high modulation efficiencies (~50%), broadband operation (~20% near the operating wavelength of 800 nanometers), and fast responses (<0.4 milliseconds). The developed MEMS-OMS platform offers flexible solutions for realizing complex dynamic 2D wavefront manipulations that could be used in reconfigurable and adaptive optical networks and systems.

Tunable metasurfaces towards versatile metalenses and metaholograms: a review

“…This mechanism has an advantage in terms of the wide tuning range of the focal length from negative to positive, compared to other mechanisms such as Alvarez lenses 98,111 and micro-electromechanical systems (MEMS). 99,[112][113][114] Other mechanical actuation mechanisms such as Alvarez lenses and tunable metalenses that integrate MEMS systems have been demonstrated. Varifocal metalenses using the Alvarez lens design have been fabricated by integrating two cubic metasurfaces; one example in particular has a tunable focal length in connections when it is laterally actuated using a translation stage [Fig.…”

Full-range birefringence control with piezoelectric MEMS-based metasurfaces

“…S3 , S4 , Methods/Fabrication). Owing to the FP nature of the designed DWP component, the overall response is inherently periodic with respect to the variable air gap T a , thus relaxing the requirement for small, nm-sized, air gaps essential for the previously developed MEMS-OMS configurations 22 and thereby simplifying the assembly process. We should however note that the access to nm-sized air gaps, although not easily gained, would allow one to operate the DWP with gap surface plasmons being generated 22 , a regime that promises a slightly broader operation wavelength range as discussed below.…”

“…Owing to the FP nature of the designed DWP component, the overall response is inherently periodic with respect to the variable air gap T a , thus relaxing the requirement for small, nm-sized, air gaps essential for the previously developed MEMS-OMS configurations 22 and thereby simplifying the assembly process. We should however note that the access to nm-sized air gaps, although not easily gained, would allow one to operate the DWP with gap surface plasmons being generated 22 , a regime that promises a slightly broader operation wavelength range as discussed below. To quantify the air gap T a at each actuation voltage V m , we make use of the air gap-dependent MEMS-OMS operation 22 by exploiting the fact that the MEMS-OMS behaves as a mirror at periodically distributed air gaps (depending on the light wavelength used) regardless of the OMS design (Supplementary Figs.…”

“…We should however note that the access to nm-sized air gaps, although not easily gained, would allow one to operate the DWP with gap surface plasmons being generated 22 , a regime that promises a slightly broader operation wavelength range as discussed below. To quantify the air gap T a at each actuation voltage V m , we make use of the air gap-dependent MEMS-OMS operation 22 by exploiting the fact that the MEMS-OMS behaves as a mirror at periodically distributed air gaps (depending on the light wavelength used) regardless of the OMS design (Supplementary Figs. S5 , S6 ).…”

“…To summarize, capitalizing on our development of the MEMS-OMS platform 22 we have demonstrated the electrically driven DWP operating in reflection with high polarization conversion efficiencies (~75%), broadband operation (~100 nm near the operating wavelength of 800 nm), fast responses (<0.4 ms) and full-range birefringence control that enables completely encircling the Poincaré sphere along trajectories determined by the incident light polarization and DWP orientation. It should be noted that, given the access to nm-sized air gaps, one can exploit the same design principle to realize the DWP with gap surface plasmons being generated 22 , a regime that promises a broader operation wavelength range (~160 nm) although probably at the expense of a lower efficiency (~50%) 22 . Importantly, the general approach developed can also be applied to design a DWP operating in transmission by using a partially transmitting MEMS mirror and placing an OMS in the middle of an FP cavity 25 .…”