Wavefront manipulation by electrically and fluidically tuned polymer metasurfaces

Active manipulation of light beams is required for a range of emerging optical technologies, including sensing, optical computing, virtual/augmented reality, dynamic holography, and computational imaging. Miniaturization of these optical components is key to facilitating their integration into a range of applications. Despite many advances, the size and weight of traditional macroscopic lenses and dynamic optical elements still take up significant space due to their use of classic optical elements. Therefore, it is highly desirable to reduce the size and weight of the dynamic optical components in such systems. Subwavelength control over the phase using ordered arrays of nanoantennae, or metasurfaces, could allow this goal to be achieved. Tunable metasurface lenses have been realized and typically use strain or thermal tuning of the entire metasurface or mechanical movement between metasurface lenses. Recent efforts have demonstrated impressive modulation of phase and color of pixel elements that could be individually actuated with high-speed microelectromechanical MEMs technology. However, these are challenging to fabricate and experience limitations in dynamic applications due to vibration instability.

Inventors at Stanford have created a hybrid polymer/metal tunable optical metasurface system, with operation in wavelength ranges from the visible to the infrared. It can reversibly tune the color and phase of reflected wavefronts through applications of stimuli, including applied voltage or application of suitable fluids to the surface of the metasurface. The tuning mechanism is non-volatile, involving changes in polymer thickness due to changes in thermodynamic equilibrium condition. . In the case of fluidic control, the fluid infiltrates into the polymer and causes a change in the swelling degree. In the case of electrochemical control, applied voltage leads to ion intercalation, modifying the swelling degree. Depending on the specific design chosen, this can result in a change of the reflected color from the metasurface, continuous tuning of the direction of the reflected beam, or on-off modulation between different diffraction orders. These ultra-thin devices can also be made with thicknesses of 500nm, much smaller than conventional optical elements that range from the millimeter to centimeter scale. Nanoscale optical elements, combined with rapid advances in electrical control systems, or microfluidic systems infrastructure, could enable the next generation of optical elements light control.