Fig. 1. Conceptual illustration of multipoint fiber-optic laser–ultrasound generation. (a) Schematic of the proposed system. (b) Structural illustration of an FCOS. (c) Transmission light field distribution of an FCOS with a 4 μm offset along the x axis. (d) Relationship curve between the energy ratio coupled from the core mode to the cladding modes and the dislocation offset of the FCOS.

Fig. 2. Core-offset units with varying dislocation sizes photographed by the fiber fusion splicer with coupling ratios of 20.2%, 28.22%, 31%, 50.3%, and 99.86%, respectively.

Fig. 3. Experimental demonstration. (a) Schematic of the experimental setup. (b) Pictures of core-offset fibers before and after chemical etching. (c) Prepared FCOS-based transducer.

Fig. 4. Laser characteristics and generated ultrasound signal. (a) Laser spectrum after passing through an EDFA. (b) Single laser pulse measured post-EDFA. (c) Laser pulse train with a 3 kHz repetition rate post-EDFA. (d) Narrow ultrasonic pulse train with a repetition rate of 3 kHz generated by the first core-offset unit. (e) Enlarged view of the ultrasonic pulse and (f) Fourier transform of the detected ultrasonic pulse.

Fig. 5. Enlarged view of ultrasonic pulse signals generated from five fiber core-offset units and their respective Fourier transforms.

Fig. 6. Correlation between diameter of core-offset region and ultrasonic intensity.