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To generate PJs with waveguides and optical fibers, solutions where a sphere is put at the end of a hollow-core optical fiber or to use an optical fiber with a shaped tip have been proposed. Optical fiber tips have several advantages: easy to move, no necessary contact with the sample and the possibility to collect backscattered light. As a result, this technique has the potential to become a major solution in industrial processes and characterization, such as sub-micron laser processing or high-resolution spectral analysis. The ICube laboratory was the first to demonstrate that PJs can be obtained using a multimode optical fiber with a shaped tip for sub-wavelength ablation. However, the photonic jet is due to the part of the power injected on the fundamental mode. The energy on the other modes is lost to the process. Due to mode coupling, this can represent 90% of the injected power when the fiber has too many modes such as 100/140 silica fiber. We can then understand the interest of working with fibers with a lower number of modes. Nevertheless, such fibers have smaller core diameters, which makes it difficult to control the fabrication of the tip. Based on an original technique, the problem has been overcome. Fibers (50/125), (9/125) and (5/125) with microlens fitting just on their cores will be presented is this study. To demonstrate the capacity of these fibers to generate PJs, the performance of beam coming out of fibers having shaped tips has been investigated using a direct imaging technique. The volume of the PJ along the optical axis has been retrieved. The three-dimensional beam reconstruction enables not only to extract the narrow width and length of the PJ, but also to investigate the role of the excitation modes, with the aim to reduce the power spreading around the PJ.
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