Multicore fiber shape sensing based on optical frequency domain reflectometry parallel measurements

The multicore fiber (MCF) shape sensing technology utilizes the strain distribution characteristics of each core to achieve the three-dimensional shape reconstruction of the fiber. However, when using distributed fiber-optic sensing technology to measure the strain of all cores, the strain distributions are measured in different time slots resorting an optical switch, leading to difficulties in synchronizing the strain distributions within the MCF and shape changes. This, in turn, affects the accuracy of shape reconstruction. To address this, we propose a multicore fiber shape sensing method based on optical frequency domain reflectometry parallel measurements that can simultaneously measure the strain of multiple cores with only one measurement. First, we use two-outer-core parallel measurements to achieve fiber three-dimensional shape reconstruction based on vector projections method. This can achieve a maximum relative error of 3.37% for shape reconstruction. Dynamic shape sensing experiments demonstrated the advantage of the proposed method in reconstructing instantaneous shapes of the MCF. Furthermore, by connecting the two outer cores and the central core in parallel, we achieve simultaneous measurement of shape and temperature, effectively reducing the impact of temperature changes on shape sensing. When the temperature increases from 40°C to 90°C, the maximum relative error of the three-core parallel measurements for shape reconstruction is 5.1%. The proposed method can improve the sensing accuracy in applications with rapidly changing fiber shapes and make the entire sensing system more compact.