Remote full-axis deformation sensing with optical vortex beam for health monitoring of infrastructures

In this paper, we discuss about multi-axis displacement measurement technique with single optical beam and its application for static and full-axis deformation sensing of civil infrastructures such as bridges and railways. Our proposing technique is based on the combined use of an optical vortex (OV) beam and correlation image sensors (CIS). Since the beam profile of OV involves definitive features known as zeros or phase singularities and they are invariant through propagation, we can encode and transmit rich information to determine geometrical relations between the sender and receiver nodes. By demodulating an amplitude and phase profile of OV using the CIS, all (three lateral and three rotational) displacement components can be determined using only a single frame of measurement. Unlike conventional laser displacement sensing techniques, the proposed scheme can be applicable to sequential and elongated structures in which sufficient baseline length is unavailable. The basic optical setup is presented and the results of the fundamental experiments are shown.