Optical force sensor based on multi-mode fiber and MIMO signal processing

Spatial division multiplexing (SDM) is currently investigated in order to overcome the capacity limit of common single-mode fibres. One approach of SDM utilizes individual transversal modes of multi-mode fibers (MMF) for data transmission. However, due to external perturbations such as bending and elongation of the optical fibre along the optical MMF link and fibre imperfections cross-talk occurs between the transversal modes and thus multiple-input multiple-output (MIMO) signal processing has to be applied at the output in order to recover each orthogonal signal at the input. In this work MIMO signal processing in combination with a graded-index (GI)-MMF are experimentally explored for force sensing. The experiments are based on a (2×2) MIMO implementation and crosstalk has been introduced by applying a micro-bender (MB) and different forces. By observing the weight-function of the MIMO system, the amount of perturbation i.e. the amount of force applied was determined. In comparison to sensors using steady state or even restricted mode launching conditions our results show that MIMO processing allows wider measurement ranges and achieves higher sensitivities.