Simultaneous ranging and force sensing on a single-mode fiber for minimally invasive interventions

We present a coaxial fiber probe that integrates optical coherence tomography ranging and fiber Bragg grating force sensing within a single-mode fiber, enabling synchronized distance-force feedback for minimally invasive interventions. A short no-core and graded-index fiber segment forms a weakly focused beam, extending the depth of focus while maintaining the probe's miniature and intrinsically aligned design. Proof-of-concept experiments first demonstrate endoscopic palpation, where the probe distinguishes stiff inclusions from surrounding tissue, and then subretinal injection, where contact and puncture are simultaneously detected as changes in distance and force. This compact coaxial architecture provides a scalable platform for integrated optical sensing in robotic microsurgery and other precision manipulation tasks.