A Microfiber Mach-Zehnder interferometer (MMZI) based on tapered seven-core fiber (SCF) for curvature measurement has been reported and demonstrated. The tapered SCF promoted the light coupling efficiency from the single-mode fiber (SMF) to the SCF, which results in the transmission spectrum with a low loss and high extinction ratio. In the process of curvature measurement, the sensitivity can reach up to 174.02957 nm/m ⁻¹ , which is the highest curvature sensitivity in the MZI with SCF as best as we have known. Furthermore, the maximum temperature sensitivity is 0.00956 nm/°C when the temperature changes from 30 °C to 140 °C. It shows that this sensor is naturally insensitive to temperature, which has a good performance in avoiding the cross-sensitivity effect between the temperature and curvature.

We propose a novel wearable knee joint angle monitoring sensor based on the Mach-Zehnder interferometer (MZI) using a triple-clad fiber (TCF), which is fabricated by directly fusing a triple-clad fiber between two single-mode fibers (SMFs). The varying motion angle of knee joint will cause various optical path differences between the fiber core mode and the cladding modes, which will lead to the wavelength shifting of the MZI. Experimental results show that the sensor can measure the bending angles of the knee joint in the range from 40 ° to 90 °. When the knee joint angle changes from 65 ° to 90 °, the angle sensitivity can reach 569 pm/degree, and the correlation coefficient can achieve 0.98. In addition, the temperature sensitivity of the proposed sensor is 69 pm/°C in the temperature range from 40 °C to 90 °C, which shows that this sensor is hardly sensitive to temperature. Thus, the cross-sensitivity effect between the temperature and curvature can be avoided. These advantages provide a potential application prospect in the areas of sports medicine rehabilitation and robot monitoring.

A high-sensitivity temperature and curvature microfiber Mach-Zehnder interferometer (MMZI) with two peanut-shaped structures is proposed and demonstrated for the first time. The interferometer consists of a section of microfiber and two peanut-shaped structures. The microfiber can be easily affected by the external environment due to its strong evanescent field on the surface and the peanut-shaped structure is conducive to excite fundamental mode to high-order mode, which is beneficial to realize high-sensitivity sensing detection. The experimental results show that the maximum temperature sensitivity of −678.67 pm $/$ °C is obtained in the range of 30 °C to 42 °C, which is the highest temperature sensitivity we have known in the peanut-shaped structure sensor. Furthermore, the sensor is also used for curvature measurements. The curvature sensitivity can be up to −79.09 nm $/\text{m}$ ⁻¹ from 0.10188 m⁻¹ to 0.20374 m⁻¹. Therefore, the proposed sensor will have good application prospects in the field of biological detection and environment monitoring due to the advantage of high temperature sensitivity.

We propose and demonstrate a new temperature and curvature sensor based on double peanut-shaped structures and tapered coreless fiber (CLF) using microfiber Mach-Zehnder interferometer (MMZI) technology. The peanut structure is comprised of single-mode fiber (SMF) and CLF, and fused sphere in each fiber end to create a high sensing performance. By combining the characteristics of the peanut-shaped structure and microfiber with a high evanescent field, this sensor can excite more high-order modes and obtain high-performance measurements. The experimental results demonstrate that the maximum intensity temperature sensitivity is 0.33 dB/°C when the temperature changes from 45 °C to 60 °C with a taper length of 5.5 mm. As far as we have known, it is the highest temperature sensitivity in the peanut-shaped structure with intensity modulation. Additionally, the sensor has an intensity curvature sensitivity reaches up to 16.56 dB/ $\text{m}^{-1}$ when the curvature varies from 0 $\text{m}^{-1}$ to 0.23264 $\text{m}^{-1}$ . These results highlight that the sensor has excellent curvature and temperature sensitivity, making it ideal for application in health monitoring, environmental monitoring, and medical applications.