Micro Displacement Sensor With Cascaded Micro Fiber Sagnac Ring Based on Vernier Effect

A cascaded micro fiber Sagnac ring (MFSR) micro displacement sensor based on the Vernier effect is proposed and studied in this article. A single-mode optical fiber is wound into a ring with a diameter of about 10 cm, an MFSR is obtained by fused tapering in the winding area, and another MFSR with a slightly different coupling length is fabricated by the same process. The transmission spectrum of each Sagnac ring is similar to the Vernier scale. The sensitivity of the sensor can be improved through the Vernier effect after the two rings are cascaded with single-mode fiber. The mode of MFSR is analyzed by using finite element analysis software. Its transmission spectrum is calculated through numerical simulation, and its micro displacement sensing characteristics are verified by experiments. Experimental results show that the micro displacement sensitivity of the sensor is as high as <inline-formula> <tex-math notation="LaTeX">${-{1.76} \,\,\text {nm}/\mu \text {m}}$ </tex-math></inline-formula> in the range of 0–<inline-formula> <tex-math notation="LaTeX">$35~\mu \text{m}$ </tex-math></inline-formula>, and its resolution is <inline-formula> <tex-math notation="LaTeX">${{0.057} ~\mu \text {m}}$ </tex-math></inline-formula>. Compared with a single MFSR, the sensitivity is improved by 7.65 times, which is consistent with the simulation. The cascaded MFSR micro displacement sensor has the advantages of low transmission loss and high measurement sensitivity and has important application prospects in industrial production and micro displacement detection.