Vortex-Bessel beam generation by 3D direct printing of an integrated multi-optical element on a fiber tip

Shaping light beams as they propagate out of the tips of optical fibers is a desired ability, as the light could be tailored for various applications in a miniaturized, integrated, and cost-effective manner. However, fabricating sophisticated refractive elements directly onto fibers is challenging. By using 3D-direct laser writing (3D-DLW), high-quality optical devices could be fabricated directly on top of the fiber's facet by the two-photon absorption process. Here, we demonstrate how a high-order Bessel beam carrying orbital angular momentum (OAM) could be generated by using this lithography process. The beam is shaped using an integrated micro-optical system that consists of a twisted axicon and parabolic lens in an adapted fiber configuration. This work provides the analysis and measurements of the generated beam, along with simulated predictions. The far-field pattern, at a distance of 2 mm from the fiber, was examined, and we have found that the size of the central ring remained nearly unchanged, as expected for this type of beam. The beam's OAM value was measured using either an interference pattern or a mode convertor. Furthermore, the near-field and far-field Bessel beam profiles were investigated simultaneously at various laser power values, reaching intensities of up to 3.8 MW/cm². This work may pave the way for future integrated beam manipulation on fibers, enabling the use of higher laser outputs.