Session B01: Optics and Materials

Flat Optics for Next-Generation Devices and Computing

Conventional optics, which are curved and bulky, have been used for hundreds of years in healthcare, aerospace and consumer markets. Over the past decade, a new type of planar nanostructured device, known as metasurfaces, has emerged as a promising platform to transform optical components into ultracompact semiconductor packages. In this talk, I will discuss how we engineer and fabricate multilayer metasurfaces to enable 3D integrated meta-optics. I will then present our efforts in translating laboratory demonstrations into real-world applications for imaging, holography and analog computing. These results offer promising avenues for advancing future consumer optoelectronic devices.   

Supersymmetric Semiconductor Laser Arrays

In recent years, the field of optics has experienced a surge of new concepts inspired by quantum field theory and condensed matter physics. In this presentation, we will talk about the concept of Supersymmetry (SUSY) in optics and its practical applications. Initially proposed within the context of high-energy physics, SUSY aims to address several unresolved questions in this field and provide a unified description of all fundamental interactions. In this regard, SUSY relates bosonic and fermionic degrees of freedom in a cohesive fashion. Even though full ramification of this theory awaits experimental verifications, the mathematical framework of SUSY has been successfully extended into other fields such as low energy physics, condensed matter physics, statistical mechanics, and more recently optics.

Here, we will demonstrate how notions derived from SUSY can be applied to create optical structures with improved and novel functionalities. In particular, we will show that SUSY techniques can be systematically employed to address one of the longstanding challenges in laser science, that is the tendency of semiconductor laser arrays to operate in a multimode fashion, which adversely affects their beam quality. By leveraging SUSY methods, we ensure that these settings lase exclusively in their fundamental mode, leading to an improved beam quality and enhanced brightness.   

Deterministic vortices evolving from partially coherent fields

In recent years, research on optical wavefield singularities has led to various applications such as micromanipulation, optical trapping, imaging, and free-space optical communications. A common singularity is the optical vortex, characterized by a line of zero intensity and a helical phase structure. Another important area of optics is optical coherence theory, with applications like intensity interferometry, ghost imaging, and optical coherence tomography. Partially coherent beams are known for their resistance to atmospheric turbulence, which is useful for improving free-space optical communications. This raises the question of whether combining optical vortices and partial coherence yields benefits, though it has been believed there is a conflict between the two. A vortex represents a deterministic phase structure in a spatially coherent field, while a partially coherent field has nondeterministic phases. Vortices can appear in two-point coherence functions (coherence vortices), but field vortices associated with zero intensity are typically absent in partially coherent fields.

It was recently found that a class of partially coherent beams, known as Rankine vortex beams, can evolve into a deterministic vortex in the far zone due to their relationship with Gaussian Schell-model vortex (GSMV) beams. However, for applications like optical manipulation and free-space optical communications, a partially coherent beam that can produce a deterministic vortex at any propagation distance is more desirable. In this paper, we demonstrate that such beams, which we call deterministic vortex beams (DVBs), can be designed using fractional Fourier transforms (FracFTs) to manifest a deterministic vortex at any range and degree of spatial coherence. 

In conclusion, we show that it is possible to create partially coherent beams with deterministic vortices at any desired propagation distance. Though this study focused on a vortex beam of order 1, higher-order vortices can be generated by modifying the order of the GSMV beam at the source. Our findings may have applications in free-space optical communication and further illuminate the relationship between coherence and singular optics.   

self-focusing circular coherent vortex beams

Studies on partial coherence have shown how structuring the statistical properties of light can change its behavior in radical ways. Circular coherence sources, which are perfectly coherent along any ring that is concentric to the beam center, have the potential to preserve the spiral phase structures of optical vortices on propagation, especially under turbulence conditions. 

In this study, we create circular coherent vortex beams by imposing circular coherence on Laguerre-Gaussian (LG) beams, which carry optical vortices. The second-order coherence properties, such as cross-spectral density (CSD), spectral density, degree of coherence, and coherence singularities (correlation vortices and ring dislocations) are investigated at the source plane and in free-space propagation up to 3km. To view the beam profiles with coherence singularities, we project the four-variable CSDs into a two-variable space by fixing one of the two observing points.

At the source plane, both amplitude and phase distributions of circular coherent vortex beams for different azimuthal orders show coherence singularities. The propagation of CSDs follow the Huygens' principle, showing its behavior at 1 km, 2 km, and 3 km, respectively. It is shown that CSDs shift toward the origin near 1 km; this is a manifestation of the self-focusing effect of the beams. When the distance is larger than 1 km, CSDs start spreading as the free-space diffraction becomes dominant. The amplitude and phase of the beams on propagation illustrate that both the zero amplitude and spiral phase structure maintain on the beam axis, a property that makes them good candidates for applications such as free-space optical communication. We also compare the propagation profile of a coherent beam (focused by a lens) and that of a circular coherent beam with the same component coherent beam. The intensity distribution of the circular coherent beam appears smoother in the focal area. Additionally, a wider range of spatial frequency might be conveyed by the circular coherent beam, which leads to another potential application for lensless imaging.