Simultaneous Bending and Twist Measurement Using a Simple Multimode Fibre Sensor with Selective Mode Excitation

Multimode optical fibres (MMFs) have emerged as versatile platforms for sensing applications due to their high sensitivity to various environmental changes, such as temperature, strain, bending, and twist. This sensitivity is primarily attributed to the generation of complex speckle patterns resulting from mode interference within the large fibre core. Several studies have explored the potential of MMFs for sensing [1], [2]. These speckles are highly dynamic and affected by various environmental changes simultaneously, making MMFs promising candidates for multi-parameter sensing. However, a major challenge lies in the fact that there is no direct mapping between the speckle changes and the corresponding sensor values. As a result, advanced machine learning algorithms are typically required to interpret the speckle changes, introducing computational overhead and complexity. To address this limitation, this paper presents a novel learning-free multi-parameter optical sensor using a single MMF. The proposed sensor enables simultaneous bending and twist measurements through a simple and effective approach, eliminating the need for complex speckle demodulation techniques.