Ultracompact and ultrasensitive fiber-tip nanoforce sensor enabled by Vernier effect and cantilever with a hole

An ultracompact and ultrasensitive force sensor based on Vernier effect is proposed that consists of a graded index fiber-based beam collimator and a 3D micro-printed force sensing probe. The probe incorporates a cantilever and a polymer half-cylinder, enabling light to propagate and split in air and cylinder paths, forming sensing and reference Fabry-Perot cavities, respectively. As such, an ultracompact Vernier effect system is constructed for sensitivity enhancement. A square hole is introduced to reduce the cantilever's second moment of area, thus further enhancing force sensitivity. As force is applied, the cantilever deflects, which is probed interferometrically with light delivered by the optical fiber. The external force can be correlated with the spectral change. A femtosecond laser-based 3D microprinting technique is applied for sensor fabrication. An ultrahigh sensitivity of 80.47 nm/μN is achieved with excellent operational stability. The proposed sensor is expected to play a crucial role in the fields of biomedical and material science, thanks to its distinct advantages, including high sensitivity, compact size, and high customizability.