Generating ultraviolet perfect vortex beams using a high-efficiency broadband dielectric metasurface

Generation and measurement of irregular polygonal perfect vortex optical beam based on all-dielectric geometric metasurface

The perfect optical vortex (POV) beam carrying orbital angular momentum with topological charge-independent radial intensity distribution possesses ubiquitous applications in optical communication, particle manipulation, and quantum optics. But the mode distribution of conventional POV beam is relatively single, limiting the modulation of the particles. Here, we originally introduce the high-order cross-phase (HOCP) and ellipticity γ into the POV beam and construct all-dielectric geometric metasurfaces to generate irregular polygonal perfect optical vortex (IPPOV) beams following the trend of miniaturization and integration of optical systems. By controlling the order of the HOCP, conversion rate u, and ellipticity factor γ, various shapes of IPPOV beams with different electric field intensity distributions can be realized. In addition, we analyze the propagation characteristics of IPPOV beams in free-space, and the number and rotation direction of bright spots at the focal plane give the magnitude and sign of the topological charge carried by the beam. The method does not require cumbersome devices or complex calculation process, and provides a simple and effective method for simultaneous polygon shaping and topological charge measurement. This work further improves the beam manipulation ability while maintaining the characteristics of the POV beam, enriches the mode distribution of the POV beam, and provides more possibilities for particle manipulation.

Creating perfect composite vortex beams with a single all-dielectric geometric metasurface

Optical vortex beam carrying orbit angular momentum has been extensively researched and applied recently. Among which a perfect vortex beam (PVB) has attracted much attention owing to its topological charge (TC)-irrelevant intensity profile. However, the morphology singularity, as well as implementation complexity of the PVB tie the degree of freedom for multiplexing. Herein, by introducing the concept of a composite vortex beam, we originally propose a novel kind of PVB - perfect composite vortex beam (PCVB) - which possesses a rosette-like intensity pattern that is exactly correlated with the TC and can be directly generated using a single all-dielectric geometric metasurface rather than bulky optical systems. We numerically simulate the broadband generation of the proposed PCVB with various TCs, sizes, and rotation angles. To further explore the potential of our design in practical applications, we demonstrated the coaxial array of the PCVBs and detected their optical angular force for manipulating nanoparticles. We believe that our fruitage may pave a desirable avenue for optical communication, information processing, and optical manipulation.

Generation of perfect optical vortex arrays by an optical pen

Recently, perfect optical vortexes (POVs) have attracted substantial attention, because they have an orbital angular momentum (OAM) and the beam diameter is independent of the topological charges. There are numerous innovative results that have been found by modulating the POV optical field. However, methods for controlling the arbitrary parameters of POV are lacking. In this paper, we use the optical pen to overcome this problem. The optical pen is a high-precision optical field modulation method construction based on the relationship between the optical path difference and phase. Based on this method, we have achieved POV arrays with controllable arbitrary parameters in free space, including the spatial position, numbers, topological charges, beam diameter, and amplitude. This work can be applied not only in the fields of optical tweezers, particle manipulation, and super-resolution microscopic imaging, but also will promote the development of optical communication, quantum information coding, and so on.

Generation of multi-channel perfect vortex beams with the controllable ring radius and the topological charge based on an all-dielectric transmission metasurface

The perfect vortex (PV) beam, characterized by carrying orbital angular momentum and a radial electric intensity distribution independent of the topological charge, has important applications in optical communication, particle manipulation, and quantum optics. Conventional methods of generating PV beams require a series of bulky optical elements that are tightly collimated with each other, adding to the complexity of optical systems. Here, making the amplitude of transmitted co-polarized and cross-polarized components to be constant, all-dielectric transmission metasurfaces with superimposed phase profiles integrating spiral phase plate, axicon and Fourier lens are constructed based on the phase-only modulation method. Using mathematical derivation and numerical simulation, multi-channel PV beams with controllable annular ring radius and topological charge are realized for the first time under circularly polarized light incidence combining the propagation phase and geometric phase. Meanwhile, perfect vector vortex beams are produced by superposition of PV beams under the incidence of left-handed circularly polarized and right-handed circularly polarized lights, respectively. This work provides a new perspective on generating tailored PV beams, increasing design flexibility and facilitating the construction of compact, integrated, and versatile nanophotonics platforms.

Plasmon mode manipulation based on multi-layer hyperbolic metamaterials

Metamaterial with hyperbolic dispersion properties can effectively manipulate plasmonic resonances. Here, we designed a hyperbolic metamaterial (HMM) substrate with a near-zero dielectric constant in the near-infrared region to manipulate the plasmon resonance of the nano-antenna (NA). For NA arrays, tuning the equivalent permittivity of HMM substrate by modifying the thickness of Au/diamond, the wavelength range of plasmon resonance can be manipulated. When the size of the NA changes within a certain range, the spectral position of the plasmon resonance will be fixed in a narrow band close to the epsilon-near-zero (ENZ) wavelength and produce a phenomenon similar to "pinning effect." In addition, since the volume plasmon polaritons (VPP) mode is excited, it will couple with the localized surface plasmon (LSP) mode to generate a spectrum splitting. Therefore, the plasmon resonance is significantly affected and can be precisely controlled by designing the HMM substrate.

Generation of perfect optical vortex by Laguerre-Gauss beams with a high-order radial index

Perfect optical vortex (POV) beams have attracted extensive attention because they have the advantage of a radial profile that is independent of orbital angular momentum. To date, it is usually obtained by means of the Fourier transform performed by a lens on Bessel beams. We theoretically and experimentally demonstrate that POV can be generated by performing the Fourier transform on Laguerre-Gauss beams with a high-order radial index. Furthermore, we derive an analytical expression for the increase in vortex radius, which is beneficial to compensate for the influence of the radius change in actual experiments. Our results may shed new light for a variety of research utilizing POV.