Sensitivity-enhanced refractive index sensor based on series structure of two microfiber knot resonators with Vernier effect

Abstract

This paper proposes and experimentally demonstrates a sensor for sensitivity-enhanced refractive index (RI) sensing based on Vernier effect. The Vernier effect achieved by connecting two microfiber knot resonators (MKRs) in series. The sensing principles and spectrum of the structure are studied theoretically and then verified experimentally. The results exhibit that the RI sensor has high sensitivity up to 3301.76 nm/RIU and it is detection resolution is 6.057×10−6 RIU. That is because the microfiber has high proportional evanescent field and Vernier effect multiplies the spectrum of individual MKR. The proposed series structure of two MKRs with high sensitivity, easy fabrication and low cost can be extensively applied to physical, chemical and biological signal detection.