Analysis of misalignment, twist, and bend in few-mode fibers using spatially and spectrally resolved imaging

Abstract Modal pattern and power in few-mode fibers, with dominant high-order modes by mode excitation at different core offset misalignments, were simulated and experimentally examined using the spatially and spectrally resolved imaging (S2) technique. The far-field specklegram of the interference between the LP11 and LP21 modes was observed. Twisting and bending characteristics of the LP11 mode in a two-mode fiber (TMF) were presented by reconstructing the LP11 mode using the S2 imaging technique. The experimental results showed that the LP11 mode specklegram rotated 76.4% of the fiber twist angle and 0.58 deg/m−1 of the fiber curvature in the TMF. The relative peak amplitude was measured to decrease the fiber twist angle by 0.009 dB/deg and the curvature by 0.056 dB/m−1. These characteristics allow for future use of the LP11 mode in fiber specklegram sensors. Additionally, the advantage of the S2 method for specklegram sensors is that it does not require the excitation of only the LP11 mode in the fiber, which simplifies the experiment.