A Zigzag-Shaped Tapered Optical Microfibers Interferometer Was Invented Operating At The Dispersion Turning Point

The dispersion turning point (DTP) in microfibers has proven to be an effective exceptional phenomenon for sensitivity improvement. In order to break the adiabaticity condition and excite higher-order modes effectively to satisfy the condition of DTP, the transition segments of tapered optical microfiber should be abrupt.

Recently, a research group led by Prof. WU Yihui from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) proposed a zigzag-shaped optical microfiber (Z-OMF) interferometer working at the DTP. This study is published in Optical Express.

The Z-OMF was fabricated in a controllable manner by applying a slight tilt angle to the optical fiber. For a Z-OMF, the asymmetric taper structure favored the excitation of the HE₁₁ and HE₂₁ modes. The beating between HE₁₁ and HE₂₁ modes occured when they traveled along the Z-OMF optical path. When the bending angle of the Z-OMF reached 1.61°, high contrast interference fringes were formed between the HE₁₁ and the HE₂₁ modes.

By optimizing the diameter of the OMF, the group effective refractive index (RI) difference between HE₁₁ and HE₂₁ mode equaled zero, satisfying the condition of dispersion turning point. At the optical fiber diameter of 2.3μm, the DTP was located at near 1300nm, and the RI sensitivity was1.46×10⁵ ± 0.09×10⁵ nm/RIU.

Compared with the tapered optical microfiber, straight conical fiber, the proposed Z-OMF is easier to obtain the condition of the DTP. The ultra-high RI sensitivity indicated that Z-OMF is a promising platform for chemical and biological sensing applications.