Vortices are natural phenomena in the natural world. Concurrently, in the study of optics, the concept of optical vortex beams (OVBs) exists. The wavefront of a vortex light exhibits a unique intensity distribution and helical phase distribution. The spatial phase correlation factor exp(ilθ) is an important feature, where l represents the topological charge (TC) and θ represents the azimuthal angle [1]. Recently, it has been found that OVBs with the orbital angular momentum of infinite orthogonal eigenmodes are theoretically capable of indefinitely accommodating the information capacity of superimposed individual photons, which can expand the application prospects of optical communication and manipulation to a new level [[2], [3], [4]]. However, the toroidal intensity distribution of OVBs is highly dependent on the number of TCs. The reason for this is the formation of a central dark hollow, i.e. a phase singularity, at the center of the vortex beam due to the uncertainty of the phase. As the number of topological charges increases, the central dark hollow of the circle gradually increases in size, causing the intensity of the vortex beam to diminish [5], which rendering it difficult to achieve the spatial superposition of different TCs in practical applications. To overcome this limitation, a perfect vortex beam (PVB) has been introduced as an ideal model for an OVB that can retain a constant toroidal intensity distribution regardless of TC variations and has garnered extensive research interest. Conventional optical devices used to generate PVBs include axicon lenses [6], interferometers [7], and digital microscopy devices [8]. However, these methods usually require a complete set of collectively large optical components that are difficult to miniaturize and integrate, which hinders their application.

Metasurface, an artificially engineered two-site metamaterial consisting of subwavelength scale nanoantennas, can regulate the amplitude, phase, and polarization of a wavefront precisely and easily [9]. The size of a metasurface is typically in the nanoscale range, and its thickness is controlled by manipulating the hierarchical structure, size, and arrangement of nanoscale particles of the material. In addition, metasurfaces offer higher flexibility and precision from the visible domain to the microwave domain [[10], [11], [12]]. Recently, with the advancement of fabrication techniques, metasurfaces have shown considerable potential in various applications such as polarization control [13], metalenses [14], vortex beam generators [15], and nonlinear optics [16]. However, when the internal parameters and structures are fixed, metasurfaces can realize only a specific function. As the current demand for tunable functionalities increases, there has been growing interest in the development of tunable metasurfaces. Phase-change and flexible materials have been used to fabricate metasurfaces [17]: phase-change materials are able to undergo a structural phase change in the presence of an external field, which is accompanied by a significant change in the optical constants, while flexible materials are able to flexibly adjust their morphology, which adds a new dimension to the manipulation of electromagnetic waves. However, the excessive amount of auxiliary equipment required to make flexible materials makes the fabrication of metasurfaces challenging. As for the halogen perovskites chosen in this paper, its feature of tunable band gap and portable size make it an excellent material for the preparation of tunable metasurfaces [18]. Although the potential toxicity of halogen perovskites limits its application to some extent, it is undoubtedly a promising material for optoelectronic applications.

As a new type of optoelectronic material, halogen perovskites have the advantages of low expenditure, a simple fabrication process, and a wide spectral absorption range [[19], [20], [21]], which are extremely well suited for lasers, nonlinear optics, and other fields [[22], [23], [24]]. Compared to traditional materials, halogen perovskites exhibit tunable bandgaps, which provide them with great development potential [25]. Thus far, researchers have successfully used the Jones matrix to elucidate the properties of halogen perovskites [26]. Further, they have prepared halogen perovskite–based metasurfaces and successfully applied them for photoluminescence and structural painting [[27], [28], [29], [30]]. In addition, dynamic, halogen perovskite metasurface holography has been experimentally validated under the reflection mode. However, few studies have been performed involving the transmission mode.

Herein, we present a high-performance switchable perfect composite vortex beam (PCVB) generator based on halogen perovskite metasurfaces that convert circularly polarized light into a parametrically tunable PCVB using a single halogen perovskite fully dielectric metasurface. This solves the PVB miniaturization problem. We first propose a new class of PVBs, namely PCVBs, whose “perfect” intensity distribution exhibits a rosette-like pattern, consisting of several TC-related petals. We then introduce the principle of the mode conversion of Laguerre–Gaussian beams (LGBs) to generate PCVBs and the theory of halogen perovskites based on geometrical phases. The overall effect of features, such as operating wavelength, TC number, and numerical aperture size, on the synthetic vortex light field is explored using FDTD solution. As the numerical aperture increases, the toroidal intensity radius of the generated PCVB increases, and as the TC number increases, the number of PCVB petals becomes twice that of the TC number. This design proves to be powerful for generating PCVBs with various operating wavelengths, diameters, and rotation angles. To further explore the practical application potential of our design, we demonstrate reversible exchange between three halogen perovskite metasurfaces by chemical vapor deposition (CVD), which achieves corresponding imaging effects at specific wavelengths. In addition, we produce a coaxial array of PCVBs. We envisage that the characteristic intensity distribution features unique to PCVB can provide new ideas for optical communication [31], manipulation of nanoparticles [32] and quantum information processing [33].