Ultra-Compact Fiber Refractive Index Probe Based on 3D Printed Fiber-Tip Dual-Ring Interferometer

We proposed a novel ultra-compact fiber refractive index (RI) probe based on a dual-ring Mach-Zehnder interferometer (MZI). The sensor was directly 3D printed on the fiber tip using femtosecond laser induced two-photon polymerization (TPP) technology. Up to 17 dB fringe contrast with sharp resonance dip is achieved, which ensures high measurement resolution. In addition, thanks to the very thin diameter of the fabricated ring waveguides, large evanescent field will be generated around the waveguides, which will contribute to a strong interaction between the transmitting light and the surrounding matter. As a result, up to 868.1nm/RIU refractive index sensitivity is obtained within the refractive index range of 1.33-1.357. The proposed ultra-compact refractive index probe sensor offers great potential for applications in the biochemical field.