Ultrasensitive interferometers based on zigzag-shaped tapered optical microfibers operating at the dispersion turning point

This work proposes and demonstrates a novel interferometric sensor based on a zigzag-shaped tapered optical microfiber (Z-OMF) working at the dispersion turning point (DTP). The Z-OMF can be fabricated in a controllable manner through a modified fiber tapering method. Our study shows that the bending taper can transfer a portion of the fundamental HE 11 mode to higher-order modes, and when the bending angle of the Z-OMF reaches 1.61°, high contrast interference fringes can be formed between the HE 11 and the HE 21 modes. More importantly, we find that by optimizing the diameter of the OMF, the group effective refractive index (RI) difference between HE 11 and HE 21 mode equals zero, and the refractive index sensing performance can be dramatically improved. To validate our proposed sensing mechanism, we experimentally demonstrate an ultrahigh sensitivity of 1.46×10 5 ± 0.09×10 5 nm/RIU. The proposed Z-OMF interferometer has the advantage of high sensitivity and low cost and shows excellent potential in chemical and biological detection.