Like phase and amplitude, polarization is a fundamental property of light, which can
reveal hidden information and has been used in many research fields, including material
science, medicine, target detection and biomedical diagnosis. Polarization generation,
detection and imaging are of importance for fundamental research and practical
applications. Although conventional optics can perform these tasks, it suffers from a
complex system, large volume and high cost, which cannot meet the continuing trend of
miniaturization and integration. Optical metasurfaces, the two-dimensional counterparts
of metamaterials, are planar nanostructured interfaces, which have recently attracted
tremendous interest in realizing ultrathin and lightweight planar optical devices. Optical
metasurfaces can manipulate light’s amplitude, phase and polarization in a desirable
manner, providing a new and compact platform to generate, detect and manipulate light’s
polarization. This thesis utilises optical metasurfaces to realise and experimentally
demonstrate novel optical devices for polarization generation, detection and imaging. Due
to the simplicity of the design and fabrication, this thesis is mainly focused on geometric
optical metasurfaces, which are superior to other types of metasurfaces.
2D and 3D polarization structures are generated based on a metalens approach. A ring
focal curve, an Archimedean spiral focal curve, and seven-segment-based decimal
numbers are experimentally demonstrated in 2D space, while a 3-foil knot, a 4-foil knot,
and a 5-foil are realized in 3D space. The geometric metasurfaces are designed based on
colour and phase multiplexing and polarization rotation, creating various 3D polarization
knots. Various 3D polarization knots in the same observation region can be achieved by
controlling the incident wavelengths, providing unprecedented polarization control with
colour information in 3D space. Novel polarization detection is experimentally
demonstrated through optical holography, light’s orbital angular momentum, and optical
ring vortex beams. The measured polarization parameters such as major axis, ellipticity,
and handedness are in good agreement with the theoretical prediction. A multifunctional
microscope is proposed and developed to image different objects, including biological
samples such as cheek cells and beef tendons. For the same sample, five images with
different optical properties are obtained on the same imaging plane, which can
simultaneously perform edge imaging, polarimetric imaging, and conventional
microscope imaging. Benefiting from the ultrathin nature, compactness and
multifunctionality of the optical metasurface devices, the integration does not excessively increase the volume of the optical system. With its promising capabilities and potential
for expandability, we believe our microscope will herald an exciting new era in
biomedical research.
The ultrathin nature of optical metasurfaces and their unprecedented capability in light
control have provided a compact platform to develop ultrathin optical devices with novel
functionalities that are very difficult or impossible to achieve with conventional optics.
The metasurface platform for polarization detection and manipulation is very attractive
for diverse applications, including polarization sensing and imaging, optical
communications, optical tweezers, quantum sciences, display technologies, and
biomedical research as well as wearable and portable consumer electronics and optics
where miniaturized systems are in high demand
