Deterministic wet etching of aspheric fiber microlenses with tunable conic geometry for tailored optical functionality.

Efficient coupling between guided optical fiber modes and radiated fields in the surrounding medium remains a fundamental limitation across photonics, sensing, and biophotonics. Micro-lensed fibers offer a promising solution, yet scalable fabrication with predictable geometry and deterministic optical performance has remained elusive. Here, we introduce laser-controlled wet-chemical etching (LCWCE), a single-parameter strategy that directly sculpts micro-lenses, from hyperbolic to parabolic and prolate elliptical profiles, on standard optical fibers. Local laser illumination establishes an axially confined etching-rate gradient, enabling sub-micrometer control of curvature and working distance independent of fiber type or internal structure. A physics-separated multiphysics framework combining wave optics, heat-transfer, and temperature-dependent etching kinetics captures the observed geometry evolution and validates the underlying mechanism. LCWCE enables milliwatt-scale, minimal-power fiber-based optical trapping, as well as minimally invasive in vivo dendritic detection and single-cell neural interrogation beyond 1.5 mm depth in live brains, transforming ubiquitous optical fibers into scalable, high-performance photonic probes.