Characterizing the bending deformation of polymer utilizing the diffraction spectrum of a holographic grating on a flexible substrate

A volume grating based holographic sensor on a flexible substrate for real-time characterization of the bending deformation of polymer has been studied. Two kinds of deformations, i.e., unilateral and bilateral bending, are analyzed by using the diffraction spectrum of a transmission grating. The dependence of the peak wavelength on the angle displacement in unilateral bending presents a linear relationship. The relation between the peak wavelength and the curvature radius in bilateral bending is also a linear relationship. The maximum bending angle is 18 deg in unilateral bending, and the curvature radius reduces to 44 mm in bilateral bending. The diffraction spectrum coverage is up to 200 nm. In straightening a curved grating, the spatial width of the rainbow spectrum presents a linear relation to the curvature radius. The sensing feedback of bending deformation provides an effective method for characterizing the bending movement of polymer. It can even qualitatively present the deformation by observing the center color and its width with the naked eye. The optical measurement of bending deformation further validates the practical applicability of the holographic sensor.