## 1 Introduction  
Despite the vast amount of literature devoted to vector beams in the last two decades, they still receive much attention due to their exciting applications [1]. Vector beams are complex structured light fields where the state of polarization is spatially variant across the beam section, giving place to phase and polarization singularities [2]. They have been proposed for a few promising applications in areas involving structured light, such as classical and quantum optical communications, particle manipulation, optical trapping, imaging and materials patterning [3]. In order to increase practical applicability, there is a necessity to develop simple, reliable, and efficient methods to generate different kinds of vector beams. Pure vector beams are the most common type. They are generated by the superposition of two orthogonal polarizations, typically the circular right (RCP) and left (LCP) polarization states, carrying an azimuthal phase \(\exp(i\ell\theta)\) of the same topological charge but opposite sign i.e., \(\ell_{R}=-\ell_{L}\). On the contrary, in hybrid vector beams (also named vectorial vortices or vector-vortex beams)different topological charges \(|\ell_{R}|\
eq|\ell_{L}|\) are encoded onto the orthogonal polarization components. They can be represented in the generalized hybrid-order Poincare sphere [4]. Various approaches have been followed to generate hybrid vector beams. One general approach is based on spatial light modulators (SLM), since they allow encoding arbitrary topological charges onto each polarization component. This is usually done by means of two SLMs [5; 6; 7] or by dividing the SLM screen in two halves [8]. While these systems offer great flexibility because they can be reprogrammed with arbitrary functions, they are bulky and introduce losses caused by the SLM pixelated structure. Other recent approaches use patterned polarizers [9], patterned retarders (q-plates) combined with polarization rotation devices [10], metasurfaces that encode a spiral geometric phase [11] or uniaxial crystals with special shapes [12]. Initial works made use of pure geometric phase elements where the retardance was adjusted to create different types of pure and hybrid vector beams [13]. Alternatively, a metamaterial q-plate can be combined with a spiral phase plate made as a refractive element [14] or encoded onto an SLM [15; 16]. Recent advances in metamaterial techniques allow encoding arbitrary topological charges onto orthogonal polarization components [17]. These elements are compact and efficient, but their performance is fixed on fabrication and cannot be tuned in real time. One particularly interesting case of hybrid vector beams are full Poincare beams [18]. These are hybrid vector beams where the topological charge is zero in one polarization component. Therefore, the entire topological charge is encoded on the orthogonal polarization. As one polarization component does not have a phase singularity, the full Poincare beam does not exhibit null intensity at the center; instead, the center is circularly polarized. Full Poincare beams have attracted much interest since they generate in the transversal plane a full set of polarization states located at different spatial coordinates. Therefore, they have been proposed for single-shot polarimetry [19]. Full Poincare beams have been generated with various techniques such as symmetrically stressed windows [18], interferometric arrangements to superimpose two Laguerre-Gauss modes [20], or by employing one single parallel-aligned liquid-crystal SLM operating in transmission [21] or within a Sagnac interferometer [22]. All these works show the great interest in developing methods to generate vector beams. Methods based on q-plate devices are particularly relevant because they are simple, compact, and efficient, a fact of utmost importance for technological applications.