Papers by Author: Hai Xiao

Abstract: The safety and reliability of critical civil infrastructures have been a major concern in all countries around the world. However, structural health monitoring (SHM) still faces a number of challenges, particularly in the area of in-and post-disaster monitoring. In addition, due to the large scale in dimension and complexity in geometry of a typical civil structure, a large number of embedded sensors are required to measure various structural and environmental parameters under normal and extreme conditions. To enhance the survivability of a sensor network for life-cycle structural health monitoring (SHM), this paper presents a novel self-healing sensor network. One Spider Orb-Web or network and one hybrid optical fiber (OF) system by combining the local and distributed OF technologies are designed to enhance the functionality of self-healing. Furthermore, three local self-healing sensor nodes, which use light switches or couplers, are designed to maintain the measuring connectivity at hot stress point. Finally, A simple Brillouin sensing network with self-healing nodes is constructed and then validated by the strain measurements of a three-point bend beam. The results show that by using self-healing sensors nodes, the stress state of the RC beam can be successively detected, even when some sensors fail or when the sensing line is broken.

Abstract: A single mode fiber assembled with a specified length graded index multimode fiber as a collimator, which is used in common-path optical coherence tomography (CPOCT) is described in this paper. Compared with conventional collimator lens, this assembled fibers structure possesses the advantages of small volume, easy to be fused or connected with other part of the CPOCT system. Furthermore, with this assembled structure an all fiber CPOCT system is constructed which has the potential to detect the internal bodily organs and tissues of human being. Numerical simulation and experiments are implemented to verify the effectiveness of this method.

Abstract: A new, common-path, in-axis concentric beam-splitting Michelson interferometer is demonstrated for optical coherence tomography (OCT), which can be used to perform high-resolution cross-sectional in vivo and in situ imaging of biological tissues. A piece of glass tube with its inner diameter smaller than the beam-width of the collimated light is used to split the light into a reference and sample beam. In order to obtain the optimal spectral interferogram of this OCT system, an infrared optical path adjustment method was introduced in this paper.