Fiber SPR micro displacement sensor based on heterocore structure of graded index multimode fiber

Abstract

Based on the self-focusing characteristics of graded index multimode fiber, a fiber SPR micro displacement sensor can be constructed, which has two bottleneck problems of difficult to fabricate and the small displacement detection range. In this paper, we proposed and constructed a new heterocore structure of graded multimode fiber-single-mode fiber-graded multimode fiber to realize the micro displacement sensing, which has stable performance and simple fabrication. By increasing the core diameter of modulation graded multimode fiber and displacement fiber, the displacement detection range of probe was increased. The simulating and testing results indicate that the SPR micro displacement sensor based on the graded multimode heterogeneous core structure can well realize the two-parameter sensing of micro displacement, and its average wavelength and light intensity sensitivity can reach 1.23 nm/μm, and 0.00576 a.u./μm respectively, the measurement resolution is 0.813μm. When using step multimode fiber with core diameter of 40μm in place of single-mode fiber as the displacement fiber, the displacement detection range reaches 50μm which is double that of the reported fiber SPR micro displacement sensor. The proposed fiber SPR micro displacement sensor well solved the two bottleneck problems above, which can be used in the field of micro displacement measurement of structural health monitoring.