Direct imaging of a photonic jet at shaped fiber tips

This Letter presents, to our knowledge, the first direct measurement of the three-dimensional distribution of photonic jets (PJs) generated by shaped-tip multimode optical fibers. A PJ at the distal end of optical fibers makes it easier to scan a sample, for lithography or optical analysis, for example, with a spot smaller than the diffraction limit. The backscattered light can also be easily collected. In this study, the volume of the PJ has been reconstructed using a stack of image planes and compared to numerical simulations. For the first time, the power distribution of the non-fundamental mode around the PJ has been observed, giving a better understanding of PJ-based laser etching using multimode optical fibers. An original 50/125 fiber with a microlens fitting just on its core has made it possible to strongly reduce the power spread compared to the thermoformed 100/140 fibers used in our previous works.