Holographic metasurfaces for imaging, trapping, sensing, and antennas applications

Abstract

Holographic metasurfaces are known for their effective manipulation of light properties. They are the two-dimensional version of bulk metamaterials and are made by artifact subwavelength meta-atoms. Their applications span diverse fields, such as data storage, anti-counterfeiting, optical displays, high numerical aperture lenses, and sensing.

This thesis delves into the exploration of holographic metasurface applications on both rigid and flexible substrates, including imaging, optical trapping, and curvature sensing over a wide wavelength range, from visible to millimeter waves. The design incorporates two types of metallic meta-atoms tailored to the different working wavelengths. This thesis provides detailed insights into the motivation, design, fabrication, and characterization processes.

In this thesis, the implementation of two types of multiplexing is presented: the environment-dependent and the shape-dependent holographic metasurfaces. The former is fabricated on a rigid substrate and allows the generation of two switchable images by varying both the surrounding medium and the incident wavelength. The latter can also generate two switchable images by bending the substrate to target curvatures, either in concave or convex shape. They provide two new ways to encode and generate information through holographic metasurfaces. We have also developed high numerical aperture holographic metasurfaces on rigid substrates, up to 1.2, for on-chip optical trapping applications. We demonstrate the ability to trap both beads and extended objects with higher trapping stiffness greater than 400 pN/µm/W, which is comparable to conventional objectives at the same numerical aperture. Finally, we have developed a holographic metasurface on a flexible substrate for curvature sensing applications that operates in the visible region. Unlike existing solutions, it eliminates the need for pre-calibration and can be mounted on target objects. The sensor consists of two distinct patterned areas that can generate two images: a reference scale and a position indicator. The position of the indicator shifts within the reference scale as the metasurface deforms, providing instant readings of its curvature.

These applications demonstrate the versatility of holographic metasurfaces, paving the way for multi-degree-of-freedom holographic encryption, a new class of multifunctional devices for lab-on-chip trapping applications, and real-time curvature monitoring. In addition, the use of flexible substrates enhances the adaptability of holographic metasurfaces, especially when adapting to non-flat surfaces for out-of-the-lab applications, as the metasurfaces can be transferred to any target object and integrated with other devices.

Date of Award	10 Jun 2024
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Andrea Di Falco (Supervisor)