DOI: 10.1002/adom.201701228 from the Fourier transformation of the Bessel–Gauss (BG) beam,[13,14] by utilizing a series of free-space bulky optical components including axicon, spiral phase plate, Fourier transform lens, and spatial… Click to show full abstract
DOI: 10.1002/adom.201701228 from the Fourier transformation of the Bessel–Gauss (BG) beam,[13,14] by utilizing a series of free-space bulky optical components including axicon, spiral phase plate, Fourier transform lens, and spatial light modulator. This fact greatly increases the optical system complexity and also hinders the device integration in OAM-based photonic circuits. Recently, plasmonic metasurfaces made of subwavelength nanoantenna arrays in thin metallic films have provided a powerful and efficient platform for manipulating the intensity, wavefront, and polarization of light beams beyond the diffraction limit.[26,27] In contrast to the bulky optical components with wavelengthdependent phase shift based on optical path difference, in the Pancharatnam– Berry phase optical elements (PBOEs), the PB phase in broadband operation originating from the geometric phase and accompanied polarization conversion is introduced.[28–34] The PBOE-based metasurfaces have been widely designed for wavefront shaping applications in making on-chip structured beam generators,[35–45] flat lenses,[46–49] ultrathin wave plates,[50–52] and holograms.[53–57] In this work, we present PBOE-based plasmonic metasurfaces made of rectangular-hole nanoantenna arrays as integrated optical beam converters for the direct generation of the focused 3D PV beams, without using bulky optical components, such as axicon, lens, and spatial light modulator. The PB phase profiles encoded on metasurfaces are uniquely designed with the combined phase distributions of axicon, spiral phase plate, and Fourier transform lens. The single ultrathin plasmonic metasurface device with compact area of 50 μm × 50 μm can create 3D PV beam in a long propagation distance and operate in a broad wavelength range from 600 to 1000 nm, which is useful in wavelength-multiplexed OAM-based optical fiber communication. For comparison, the previously demonstrated PB phase element system used to produce PV beams contains three in-sequence metasurface plates with efficient diameters ≥6 mm fabricated in glass boards, with the single operating wavelength at 632.8 nm.[13] It is shown that the obtained PV beams have the almost constant vortex ring radius and the same beam divergence for different TCs. We also demonstrate that the PV beam structures can be easily adjusted by varying several control parameters in the metasurface design including axicon period, lens focal length, and operation wavelength. Furthermore, multiple PV beams with Perfect vortex (PV) beams possessing annular intensity profiles independent of topological charges promise significant advances in particle manipulation, fiber communication, and quantum optics. The PV beam is typically generated from the Fourier transformation of the Bessel–Gauss beam. However, the conventional method to produce PV beams requires a series of bulky optical components, which greatly increases the system complexity and also hinders the photonic device integration. Here, plasmonic metasurfaces made of rectangular-hole nanoantennas as integrated beam converters are designed and demonstrated to generate focused 3D PV beams in a broad wavelength range, by combining the phase profiles of axicon, spiral phase plate, and Fourier transform lens simultaneously based on the Pancharatnam–Berry phase. It is demonstrated that the PV beam structures can be adjusted by varying several control parameters in the metasurface design. Moreover, multiple PV beams with arbitrary arrangement and topological charges are also produced. These results have the promising potential for enabling new types of compact optical devices for tailoring complex light beams and advancing metasurfacebased functional integrated photonic chips.
               
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