Fig. 1. (a) Fabrication procedure of the microfiber-based ultrasound sensor. (b) Micrograph of the prepared microfiber.

Fig. 2. The diagram of ultrasound detection system.φ: Phase modulator. BPD: Balanced photodetector. DC: Direct current signal. AC: Alternating current signal. DAQ: Data acquisition card.

Fig. 3. (a) Time response of the sensor to an ultrasound pulse. (b) Ultrasound pressure sensitivities of microfiber sensor and SMF sensor.

Fig. 4. (a) Recorded signals in response to broadband ultrasound wave. (b) Measured frequency responses of the microfiber-based ultrasound sensor.

Fig. 5. The short-term and long-term stability of the microfiber-based ultrasound sensor.

Fig. 6. Schematic of the photoacoustic tomography imaging system. L1&L2: Lens. R: Reflector.

Fig. 7. Images of three human hairs using the photoacoustic tomography system. (a, b) The sensor is placed perpendicular and parallel to hairs in the axial and lateral resolution measurements, respectively. (c, d) The reconstructed images of the hairs corresponding to (a) and (b), respectively. (e, f) The axial and lateral resolutions at different imaging depths.