MEMS Tunable Optical Metasurfaces

19th International Congress on Artificial Materials for Novel Wave Phenomena – Metamaterials 2025 Amsterdam, The Netherlands, Sep. 1st –6th, 2025 MEMS Tunable Optical Metasurfaces C. Meng1, Paul C. V. Thrane1,2, F. Ding1, Sergey I. Bozhevolnyi1 1 Centre for Nano Optics, University of Southern Denmark, Campusvej 55, Odense DK-5230, Denmark 2 SINTEF Microsystems and Nanotechnology, Gaustadalleen 23C, 0737 Oslo, Norway [email protected] Abstract – Electrically tunable metasurfaces offer significant potential for miniaturized, smart, and adaptive optoelectronic systems. Here, we present the concept, simulation, and experimental realization of our MEMS-OMS platform, enabling efficient and fast dynamic two-dimensional light field manipulation. We highlight two implementations: a MEMS-tunable waveplate for full-range birefringence control and a MEMS-tunable bilayer metasurface for dual-state reflection phase control. These components pave the way for highly efficient tunable optical metasurfaces, with applications in advanced imaging, interferometry, laser machining, and freespace optical communications. We foresee this platform playing a key role in next-generation reconfigurable photonic technologies. I. INTRODUCTION Dynamic optical metasurfaces (OMS) are at the cutting edge of next generation integrated and intelligent optical systems and networks, thanks to their ultra-compact and flexible design and adaptable functionalities [1]. The development of dynamic OMS has been greatly enhanced by the integration of active materials such as twodimensional (2D) materials, phase-change materials (PCMs), and liquid crystals (LCs) [2]-[4]. However, striking the optimal balance between multiple performance metrics including absolute and modulation efficiency, response speed as well as material robustness and reliability remains a challenge. For example, OMS employing 2D materials exhibit fast response times but often suffer from limited modulation depth. In contrast, those utilizing PCMs and LCs can achieve stronger modulation but typically operate at slower speeds, not to mention that LCs exhibit polarization-dependent responses and its response is also sensitive to temperature. In a recent breakthrough, we introduced a MEMS-OMS platform that combines a piezoelectric MEMS mirror with a plasmonic OMS, resulting in an ultra-compact and flexible configuration capable of dynamically tuning light field in reflection [5]-[11]. This approach delivers high efficiency, strong modulation capability, and rapid response times of up to 100 kHz, as demonstrated in our experiments. We have successfully realized diverse tunable optical functionalities for dynamic wavefront, polarization, chirality control, and very recently demonstrated its integration of MEMS-OMS within laser cavities for mode-switchable vortex lasers. Here, we present the main concept, simulation and experimental methodology of our MEMS-OMS platform, focusing on two key MEMS-OMS implementations: (1) a tunable waveplate for full-range birefringence control, achieving high efficiency (> 75%) for versatile polarization conversion [7]; (2) a tunable bilayer OMS for dualstate 2D phase control, for polarization-dependent and independent reconfigurable optical functions, which features high reconfigurable quality in terms of efficiency and speed while maintaining a remarkably with very simple electrical control mechanism [11]. II. MEMS TUNABLE WAVEPLATE FOR FULL-RANGE BIREFRINGENCE CONTROL Dynamic polarization control is essential for emerging highly integrated photonic systems, with various metasurfaces being explored for its implementation. These approaches typically rely on the birefringence properties of either natural materials or metasurfaces composed of anisotropic meta-atoms. However, due to the limited thickness of available OMS (i.e., interaction length) and inherent birefringence constraints, identifying an optimal OMS configuration remains a complex and challenging task. Moreover, existing solutions often suffer from drawbacks such as slow response times, narrow bandwidths, limited birefringence tunability, and low polarization conversion efficiencies. 19th International Congress on Artificial Materials for Novel Wave Phenomena – Metamaterials 2025 Amsterdam, The Netherlands, Sep. 1st –6th, 2025 Figure 1. MEMS-OMS tunable waveplate. Capitalizing on our development of piezoelectric MEMS-OMSs, we demonstrate electrically controlled fullrange birefringence by integrating a plasmonic OMS with precisely designed anisotropic meta-atoms and a thinfilm piezoelectric MEMS mirror [7], as shown in Fig. 1(a). The OMS component consists of a glass substrate supporting an OMS layer with a 2D array of identical rectangular gold nanobricks. Positioned in close proximity to an actuated MEMS gold mirror, its separation distance T a from the OMS is precisely controlled via an applied actuation voltage 𝑉𝑉𝑉𝑉. The resulting MEMS-OMS-based tunable wave plate operates in reflection, offering continuously tunable anisotropy and enabling complete traversal of the Poincaré sphere, thereby allowing for dynamic polarization conversion, including transitions from linear to circular polarization, orthogonal linear states, and opposite circular polarizations, as shown in Fig. 1(b). In addition, this system achieves high polarization conversion efficiencies (~75%), broadband operation (~100 nm around the 800 nm wavelength), and rapid response times (<0.4 milliseconds). III. MEMS TUNABLE BILAYER METASURFACE FOR DUAL-STATE PHASE CONTROL Most existing tunable OMSs can dynamically control only one functionality encoded in the OMS design, thus facing substantial challenges in achieving multiple reconfigurable functionalities. This limitation stems from the underlying mechanism: in most existing tunable OMSs, dynamic response is realized by actively tuning the meta-atom resonances, which in turn modifies the phase response. However, due to the high density of subwavelength-sized array elements arranged in nanometer-thin planar configurations, redefining the resonances of individual elements independently presents enormous technological challenges, rendering it practically unfeasible. In recent years, pixelated tunable OMSs have shown significant potential for fully reconfigurable meta optics [12]-[14]. However, owing to the substantial fabrication and control complexity, these OMSs are designed with control electrodes and/or meta-atoms connected along a single dimension, inherently limiting phase control to one-dimensional (1D) with polarization-dependent responses. Additionally, some of these configurations suffer from limited efficiency [14]. Therefore, dynamic efficient 2D phase control remains elusive. Figure 2. MEMS tunable bilayer metasurface for dual-state phase control Here, we integrate a thin-film piezoelectric MEMS mirror with a plasmonic bilayer OMS (BMS) in an electrically actuated, tunable topological MEMS-BMS platform that enables complete dual-state reflection phase transformation by adjusting the MEMS-BMS separation [11], as shown in Fig. 2(a). In this configuration, dualstate phase transformation is achieved by positioning the BMS at two distinct locations within the interference 19th International Congress on Artificial Materials for Novel Wave Phenomena – Metamaterials 2025 Amsterdam, The Netherlands, Sep. 1st –6th, 2025 pattern above the MEMS mirror, as shown in Fig. 2(b). In one state, only the MS1 layer interacts with incident light, while in the other, both MS1 and MS2 layers contribute to the overall response, thereby enabling the switch between two distinct functions via MEMS actuation. 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