Optical coupling between single core to multi-core optical fibers usually takes place by means of optical fiber fan-ins / fan-outs, delicate free space optics, or laser inscribed freeform waveguides. In the present work, the two-photon polymerization technique is used for the first time to create a waveguide manifold on top of a four-core optical fiber tip as a means to couple light into and from a single core optical fiber, in a fast and low-cost fashion. It is demonstrated that the performance is influenced by the numerical aperture mismatch between the fabricated and the coupled waveguides. Insertion losses below 5 dB are observed when the numerical aperture mismatch is minimized, with further reduction potential, making this approach applicable to sensing or tweezer applications.

A novel endoscopic palpation tool (EPT), designed for tactile and stiffness sensing using fiber Bragg gratings (FBGs) was evaluated in a surgical environment for intraoperative safety and effectiveness. The EPT consisted of four FBGs arranged in a cross pattern and embedded within an elastic, hollow, silicone hemispherical dome designed to deform upon contact with soft tissue. The EPT was employed to scan both in vivo and ex vivo tissue samples. Monitoring of porcine vital signs during minimally invasive and open surgical procedures showed no significant changes during use of the EPT. Perioperative blood tests including inflammatory markers and liver and renal function studies were unremarkable. Histopathological analyses of tissues involved (liver, spleen, bowel, and abdominal wall) showed no evidence of inflammation, necrosis, or tissue damage, confirming the device’s biocompatibility. To the best of our knowledge, this is the first study reporting in vivo stiffness measurements using an FBG-based EPT. The probe successfully distinguished between soft and hard tissue regions’ relative stiffness. Furthermore, successive measurements on liver samples demonstrated the device’s ability to generate stiffness maps, enabling clear visualization of spatial variation in tissue stiffness.