Flexible holographic metasurfaces for shape dependent imaging and curvature sensing

Flexible holographic metasurfaces offer significant versatility in optical imaging applications due to their ability to conform to non-flat objects and effectively manipulate optical properties. In this paper, we present the design, fabrication, and characterization of two functional imaging applications that utilize flexible holographic metasurfaces when the substrate radius of curvature is comparable to or much larger than the metasurfaces. For the first application, shape-dependent conformable holographic metasurfaces operate in the millimeter wavelength range. The images can be encoded with the target curvature and, more interestingly, the metasurface can encode two independent images within a single hologram. By bending the substrate to either a convex or concave shape, two switchable images can be revealed. The other application is a self-calibrated curvature sensor that operates in the visible range. The sensor consists of two distinct areas formed by metasurfaces that generate images of a two-dimensional reference scale and a dot image. The dot image acts as a displacement indicator and shifts within the scale as the metasurface deforms, providing an instant readout of the radius of curvature of an object that hosts the sensor on its surface, without the need for pre-calibration process. These two demonstrations expanded the use of metasurfaces for out-of-lab applications, particularly in tunable optomechanical sensors for radar and antennas, and in real-time curvature monitoring.