Transverse Offset Based Single-Multi-Single Mode Fiber Structure for Vector Rotation Sensing

In this paper, we develop an alternative all-fiber interferometer, which is based on a commercial graded-index multimode fiber mismatch spliced between two single-mode fibers. Compared to the conventional single-multi-single mode fiber structure with all of the fibers perfectly aligned, theoretical analysis shows that more power is coupled into the LP11 mode while less power is coupled into the LP01 mode, resulting in a power balance between these two modes and a higher interference extinction ratio. Experiments have been carried out to evaluate the performance of the proposed structure, and the experimental results show that the extinction ratio in the transmission spectra can be obtained with a value higher than 15 dB. Moreover, the results indicate that the output power of the proposed scheme is polarization dependent. Based on this polarization-dependent behavior, we propose a Michelson interferometer scheme which can be used as a vector rotation sensor providing a sensitivity of approximately 0.0077 nm/degree in the rotation range of 0 to ±180° with a linearity higher than 99%. Our sensor has the advantages of low-cost, simple manufacture and ease of implementation, making it widely used in engineering applications such as shape sensing and structural health monitoring.