Multipoint and Energy-Equal Fiber-Optic Laser-Ultrasonic Actuator Based on Peanut-Shaped Structures

Abstract

Laser-ultrasonic excitation holds promising prospects in nondestructive testing and structural health monitoring. This paper proposes a multipoint, energy-equal laser-ultrasonic actuator based on multiple peanut-shape (PNS) structures in a single mode fiber link. The PNS structures were fabricated by fiber micro-matching operations using a fiber splicer. The PNSs effectively couple the laser energy from the core mode into the cladding modes in the fiber. Moreover, the coupling ratio can be adjusted by controlling the taper diameter of the PNSs. For energy control, multiple PNS structures are fabricated and connected in order from small to large coupling ratios. Experiments were performed on an actuator with four PNSs of different taper diameters (138.71 $\mu \text{m}$ , 143.42 $\mu \text{m}$ , 158.23 $\mu \text{m}$ , and 180.19 $\mu \text{m}$ ) distributed along a single fiber. With its simple structure, energy control, and multipoint functionality, this all-fiber laser-ultrasonic actuator shows great potential in future multipoint ultrasound applications.