Allowing subwavelength-scale-digitization of optical wavefronts to achieve complete control of light at interfaces, metasurfaces are particularly suited for the realization of planar phase-holograms that promise new applications in high-capacity information technologies. Similarly, the use of orbital angular momentum of light as a new degree of freedom for information processing can further improve the bandwidth of optical communications. However, due to the lack of orbital angular momentum selectivity in the design of conventional holograms, their utilization as an information carrier for holography has never been implemented. Here we demonstrate metasurface orbital angular momentum holography by utilizing strong orbital angular momentum selectivity offered by meta-holograms consisting of GaN nanopillars with discrete spatial frequency distributions. The reported orbital angular momentum-multiplexing allows lensless reconstruction of a range of distinctive orbital angular momentum-dependent holographic images. The results pave the way to the realization of ultrahigh-capacity holographic devices harnessing the previously inaccessible orbital angular momentum multiplexing.

Featuring low threshold current, circular beam profile, and scalable fabrication, vertical cavity surface emitting lasers (VCSELs) have made indispensable contributions to the development of modern optoelectronic technologies. Manipulation of electromagnetic fields with emerging flat optical structures, namely metasurfaces, offers new opportunities to minimize complex optical systems into ultra-compact dimensions. Here, we proposed and experimentally demonstrated Vertical Cavity Metasurface-Emitting Lasers (VCMELs) through the monolithic integration of high-index metasurfaces, characterized by their remarkable spatial controllability over the laser beams. Such wafer-level monolithic integration of metasurfaces through VCSELs-compatible technology not only considerably simplifies the assembling process but also preserves the laser characteristics, with 2 great potential to promote various wide-field applications of VCSELs such as optical data communication, ultra-compact light detection and ranging (LiDAR), 3D sensing, and directional displays. Introduction: Vertical-cavity surface emitting lasers (VCSELs) have experienced a soaring development over the last 30 years, particularly after the demonstration of the first continuous-wave (cw) room-temperature device. 1-3 Their unique features such as low-power consumption, circular beam profile, wafer-level testing, large-scale two-dimensional (2D) array have made them the most versatile laser sources for a large number of applications ranging from optical communications, to instrumentation, as well as laser manufacturing and sensing. 4-6 The exploding application demands and the rapidly growing markets pose a longstanding challenge to further improve their performance while realizing precise beam control. In this context, the replacement of the top reflector with resonant structures and the incorporation of photonic crystal have been extensively employed to tune the emission, achieve high brightness,respectively. Meanwhile, considerable attention has been paid to improve the beam quality of the VCSELs, for example, by preventing high-order transverse modes 7-11 .Despite the fact that single-fundamental-mode laser can be realized by limiting the active region with a reduced oxide aperture, strong diffraction effect produces highly

Optimization of the performance of flat optical components, also dubbed metasurfaces, is a crucial step towards their implementation in realistic optical systems. Yet, most of the design techniques, which rely on large parameter search to calculate the optical scattering response of elementary building blocks, do not account for near-field interactions that strongly influence the device performance. In this work, we exploit two advanced optimization techniques based on statistical learning and evolutionary strategies together with a fullwave high order Discontinuous Galerkin Time-Domain (DGTD) solver to optimize phase gradient metasurfaces. We first review the main features of these optimization techniques and then show that they can outperform most of the available designs proposed in the literature. Statistical learning is particularly interesting for optimizing complex problems containing several global minima/maxima. We then demonstrate optimal designs for GaN semiconductor phase gradient metasurfaces operating at visible wavelengths. Our numerical results reveal that rectangular and cylindrical nanopillar arrays can achieve more than respectively 88% and 85% of diffraction efficiency for TM polarization and both TM and TE polarization respectively, using only 150 fullwave simulations. To the best of our knowledge, this is the highest blazed diffraction efficiency reported so far at visible wavelength using such metasurface architectures.