Micro-/nano-displacement and force sensor based on elastic rhombus-shaped structures fabricated on fiber tip using two-photon-polymerization

In this paper, we propose an intrinsic fiber-optic micro-/nano-displacement and force probe in which two cascaded Fabry-Perot (F-P) cavities are directly printed on the fiber tip using the two-photon polymerization lithography technique. This probe operates based on the so-called Vernier effect. Thus, shifts of the periodic spectral envelops are interrogated in response to the micro-displacements of the fiber probe as well as the force applied to the probe. Experimentally, for micro-displacement sensing, the sensitivity was characterized as 155.25 nm/µm and for microforce sensing, the sensitivity was found to be 0.392 nm/µN. Compared to the extrinsic F-P fiber sensors, the proposed fiber probe could be directly placed in contact with micro-objects of interest to measure the corresponding displacements and forces, which is significantly favorable for its practical applications. Advantages of the proposed sensor include ease of operation, high sensitivity, great flexibility, and small footprint.