Fiber-optic micro-displacement sensor probe based on Vernier effect

In this paper, we propose an intrinsic fiber-optic displacement 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 microdisplacements of the fiber probe. Experimentally, the sensitivity of the sensor probe was characterized as 24.6 nm/μm, that is comparable to the highest sensitivity of the previous counterparts. 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, which is significantly favorable for its practical applications. Advantages of the proposed sensor include ease of operation, high sensitivity, great flexibility, and small footprint.