The doctoral dissertation in the field of Photonics will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus.
What is the topic of your doctoral research? Why is it important to study the topic?
The research focuses on the physical nature of vortex beams and the methods for their generation and manipulation using metasurfaces. Vector vortex beams are a class of light fields with helical wavefronts carrying both orbital angular momentum (OAM) and spin angular momentum (SAM). These two forms of angular momentum represent fundamentally different aspects of light: OAM is a global property associated with the beam鈥檚 helical phase structure and topological features, while SAM is a local property determined by the light鈥檚 polarization state.
In my work, I study a special type of vector vortex beams in which the polarization varies continuously on propagation. This variation gives rise to an additional geometric phase, known as the Pancharatnam鈥揃erry (PB) phase. Such beams can be efficiently generated by means of metasurfaces, which typically consist of a large array of subwavelength nanostructures. Through engineering the local orientation and geometry of each unit cell, metasurfaces allow precise control over the beam properties, enabling compact and versatile manipulation of OAM, SAM, and the polarization structure. This research contributes to the rapidly evolving field of structured light and provides new tools for a wide range of applications in modern optics, including optical communication, quantum information, and advanced imaging.
What are the key findings or observations of your doctoral research?
The key novelties of the research are summarized as follows:
1. Designed an innovative metasurface-based Fresnel zone plate that achieves high-efficiency achromatic focusing, addressing chromatic aberration challenges in traditional optics.
2. Developed a metasurface-based two-dimensional (2D) Dammann grating capable of uniform beam splitting with high conversion efficiency and polarization insensitivity.
3. Addressed the concept of vector vortex beams with dynamically varying polarization states, achieved through advanced metasurfaces, enabling full coverage of the higher-order Poincare sphere.
4. Introduced the geometric PB phase from the self-evolving behavior of vector Bessel beams.
5. Identified a conservation law where the sum of the geometric phase, SAM, and OAM remain constant, regardless of beam鈥檚 polarization state.
6. Developed a trifunctional metasurface for perfect vectorial vortex beam array generation, enabling diffraction-related and spin-dependent topological charge control, offering enhanced structured light field command.
These findings provide new insights into the angular momentum and geometric phase of vortex beams and the application of metasurfaces, advancing the understanding of spin鈥搊rbit interactions, light polarization, optical phases, and structured light manipulation.
How can the results of your doctoral research be utilised in practice?
The metasurface-based optical elements developed in my research offer compact, efficient, and highly tunable alternatives to traditional optics. They can be applied in various practical fields -- for example, achromatic lenses for cameras and smartphones, beam shapers for optical communication and lidar, and structured light generators for holography and quantum information.
What are the key research methods and materials used in your doctoral research?
The research is conducted through two primary methods: theoretical analysis and numerical simulation. Theoretical analysis is carried out within the framework of classical electrodynamics, where the beam鈥檚 propagation behavior is studied in detail, and key features such as polarization dynamics and energy flow are explicitly derived. On the simulation side, the finite-difference time-domain (FDTD) method is employed to evaluate the performance of the proposed metasurface-based optical elements, which allows us to directly measure the intensity and phase of the modulated electric field.
The doctoral dissertation of Jiaqi Yang, MSc, entitled Design and simulation of vector vortex beams via metasurfaces will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus. The opponent will be Professor Zeev Zalevsky, Bar-Ilan University, Israel, and the custos will be Professor Ari T. Friberg, 91天美. Language of the public defence is English.
For more information, please contact:
Jiaqi Yang, jiaqi.yang@uef.fi, +358 417 028 438
- Public examination
- (PDF)
