Liquid crystal anisotropic axicon for the generation of non-diffracting Bessel beams with longitudinally varying polarization

•We demonstrate a liquid-crystal element with a linear phase profile along the radial coordinate, which can be tuned by applying different Vrms values.•In combination with a regular refractive axicon, it behaves as an anisotropic axicon, generating the collinear superposition of two orthogonally polarized Bessel beams with different propagation constant. This results in a Bessel beam where the state of polarization varies along propagation.•We show that the longitudinal polarization modulation of the Bessel beam generated by this compound anisotropic axicon is tunable by means of the addressed voltage.•The measured periods of the SOP variation are within centimeters and match quite well the theoretical model. Furthermore, the polarization splitting caused by the LC axicon has been observed in the Fourier transform domain.•The results represent a new, compact and very efficient way of producing polarization varying Bessel beams with tunable polarization modulation, in comparison to other methods reported in the literature that require bulk optical systems.•These polarization oscillating non-diffracting beams are of interest in applications such as free-space optical communications, materials processing and optical traps. In this work we demonstrate a tunable liquid-crystal element of linear phase profile along the radial coordinate. In combination with a regular refractive axicon, it behaves as an anisotropic axicon, generating the collinear superposition of two orthogonally polarized Bessel beams with different propagation constant. This superposition results in a Bessel beam where the state of polarization (SOP) varies periodically along propagation. Experimental results probe the voltage control of the SOP oscillating period, which agree well with theory. This compound axicon is a very compact and efficient way of generating Bessel beams with polarization modulation, thus representing a significant advantage over other methods reported in the literature that require bulk optical systems based on spatial light modulators.