The Lab-on-Fiber technology is giving an important contribution to the development of compact and minimal invasive devices for biomedical applications. By exploiting the high degree of miniaturization combined with the biocompatibility of the materials used, these devices can be integrated inside medical needles and taken in the human body for in vivo diagnosis and treatments, with important advantages in terms of performances, effectiveness and invasiveness. In this framework, with a look toward high-resolution ultrasound based imaging, here we analyze a novel Lab-on-Fiber 3D micro-structure for ultrasound detection, consisting in a polymeric membrane sustained by six pillars, directly integrated above the tip of a standard single mode fiber. Such a structure essentially works as a Fabry-Perot cavity, providing interference fringes in the fiber reflection spectrum, which shift accordingly with the structure vibrations caused by the incident acoustic waves. Our numerical studies, based on finite element method, demonstrated that by opportunely dimensioning the geometrical parameters involved it is possible to tune the working frequency range up to tens of MHz, reaching sensitivities higher than the standard configurations proposed so far, given by a polymeric slab directly attached above the fiber tip. Interestingly, the investigated structure can be effectively realized by exploiting the Two-Photon polymerization technique directly applied to the optical fiber tip.
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