Analysis of multimode POF gratings in stress and strain sensing applications

Polymer fiber Bragg gratings (FBGs) are made using the modified sagnac system with a 355 nm pulsed laser from a photosensitive polymer optical fiber (POF) with external and core diameters of 290.6 and 21.0 μm, respectively. Multimodes are reflected based on the reflection spectra of the gratings. The reflectivity spectra are also studied when such multimode polymer FBGs are subjected to axial static stress and strain. The respective effects of stress and strain on the sensor are decoupled and analyzed independently. Experiments and regression show that the effect of stress and the relaxation of stress in multimode FBGs (MM FBGs) in POF during loading and unloading have a more evident non-linear effect than that of strain. These non-linear properties make FBGs attractive for mechanical sensing applications.

Research highlights
► MM FBGs in POF are used as a stress and strain sensor.
► Such kind of POF sensor has different response to stress and strain, respectively.
► The effect and the relaxation of stress have a more evident non-linear effect than that of strain.