Fraxicon composite fiber probe design for OCT imaging concurrent enhancement

Optical coherence tomography (OCT) fiber probes are critical for assessing internal cavity organs and investigating pathogenesis, but balancing large starting focal length, extended depth of focus (DOF), and high lateral resolution remains challenging in miniaturized designs. Here, we present an ultra-compact (outer diameter ∼ 383 μm) optical probe with a hybrid micro-lens architecture to address these conflicts. Fabricated via two-photon polymerization (TPP) based on femtosecond laser direct writing, the design integrates a negative axicon and Fresnel axicon (fraxicon) at the tip of a fiber composite assembly, which employs a large diameter no core fiber (LD-NCF) to expand the beam from a single-mode fiber (SMF). The negative axicon enhances the starting focal length, while the fraxicon resolves the DOF-lateral resolution trade-off. The prototype achieves a ∼ 415 μm starting focal length, sub-5.71 μm lateral resolution over a 304 μm DOF, and validated performance in multi-sample OCT imaging, highlighting its commercial potential for internal cavity imaging.