Optical singularities are dark regions of a light field that exhibit rich and nonintuitive behaviors such as local wavenumbers that far exceed the light field wavenumber. For example, helical beams have a one dimensional singularity along the axis of the optical vortex where the phase is undetermined. We demonstrate that both phase and polarization singularities can be engineered and that in addition to the common one-dimensional string-like topologies, we can produce a broader family of 0D (point) and 2D (sheet) singularities. As a potential application, we design an array of point singularities to serve as identical blue-detuned cold atom traps with three-dimensional confinement. Singularity engineering imbues microscale wavefront engineering tools with the ability to produce exotic forms of light deterministically and on-demand and has wide applicability to other wave-like systems in physics.
Metasurfaces are arrays of artificially engineered subwavelength nanostructures. Owing to the strong form birefringence of these nanostructures, metasurfaces provide a fascinating platform to realize novel polarization optics. Recently, we proposed a more general design strategy for polarization-dependent metasurfaces using Fourier optics principles applied to the Jones calculus. We use this to design metasurface devices with arbitrarily chosen polarization responses embedded on diffraction orders, such as polarizers, waveplates, and cases that are mixtures of the two. We fabricate these gratings (for operation at visible wavelengths) and test them with Mueller matrix polarimetry, showing agreement with design.
Dielectric metasurfaces, which consist of spatially distributed sub-wavelength structures that impart controlled local phase shifts to the exiting light, allow access to modifying the wavefront and achieve desired function of the output beam. By adjusting the sub-wavelength structures’ shape, size, and choice of material, one can locally control the effective refractive index that affects the output light’s phase, amplitude, and dispersion, allowing various degrees of freedom in design parameters. The first generation of metasurfaces consisted of individual lab prototypes that in crucial parts relied on electron beam lithography, which severely restricted scalability. Meanwhile, mask-based methods such as deep UV lithography have been successfully adopted. While such methods open the door to high-throughput fabrication of metasurfaces, they are still limited in their achievable sample dimensions due to size restrictions imposed by wafer-based methods. By using roll-to-roll (R2R) methods, we were able to make large area metasurfaces that could find their use in displays and AR/VR applications, for example. In addition, R2R creates a lower cost method of manufacture for large volumes. In order to utilize R2R methods, there are two important challenges to overcome. First, the pattern must be extended over the large area of a film surface. Second, standard metasurface designs need to be adapted to the material and process constraints of R2R manufacturing. The R2R fabrication route is an extension of large-scale industrial processes that can produce wide format rolls of film.
Solar energy has been sought as one of the prominent candidates among the energy harvesting methods. The energy conversion efficiency of solar cell is limited by its ability of harvesting energy from limited range in solar energy spectrum. We approach this issue by using the down-conversion effect with conventional CdSe quantum dots (QDs), increasing probability of electron-hole generation in designated solar cell. In our study, we fabricated GaAs single junction solar cells and applied QDs for down-conversion. We examine the effects of such application on the solar cell properties with various methods including TR-PL technique.