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

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 HE₁₁ 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 HE₁₁ and the HE₂₁ modes. More importantly, we find that by optimizing the diameter of the OMF, the group effective refractive index (RI) difference between HE₁₁ and HE₂₁ 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 1.46×10⁵ ± 0.09×10⁵ 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.