Single-photon three-dimensional microfabrication through a multimode optical fiber

Two-photon polymerization (TPP) processes have enabled the fabrication of advanced and functional microstructures. However, most TPP platforms are bulky and require the use of expensive femtosecond lasers. Here, we propose an inexpensive and compact alternative to TPP by adapting an endoscopic imaging system for single-photon three-dimensional microfabrication. The wavefront of a visible continuous-wave laser beam is shaped so that it focuses into a photoresist through a 5 cm long ultra-thin multimode optical fiber (∅70 μm, NA 0.64). Using this device, we show that single-photon polymerization can be confined to the phase-controlled focal spot thanks to the non-linearity of the photoresist, likely due to oxygen radical scavenging. Thus, by exploiting this non-linearity with a specific overcuring method we demonstrate single-photon three-dimensional fabrication of solid and hollow microstructures through a multimode fiber with a 1.0-μm lateral and 21.5-μm axial printing resolution. This opens up new possibilities for advanced and functional microfabrication through endoscopic probes with inexpensive laser sources.