Fiber-optic ultrasound transmitters can be used in structural health monitoring, material characterization, and biomedical imaging. However, the bandwidth of current fiber-optic ultrasound transmitters is tens of MHz which prevents the ultrasound image on cells with resolution of $\mu \text{m}$ level. Here, ultra-compact in-fiber ultrasound transmitter is proposed by using the multi-mode interference in the curved UV-cured adhesive waveguide, which is fabricated between two fiber endfaces over a sandwiched core-offset spliced fiber segment. The curved adhesive waveguide can improve the contrast of device reflection spectrum from 2.7 dB to 21.7 dB. The ultrasound is generated by optical pulse excitation via photoabsorption and thermal expansion of UV-cured adhesive, and then detected via the multi-mode interference of the same waveguide with hundreds of Hz to 306 MHz broad transverse acoustic waves. This ultra-compact and cost-effective device offers new opportunities to the advanced biomedical and ultrasound-based applications.

中文翻译：

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基于弯曲胶波导多模干涉的光纤超声发射机

光纤超声发射器可用于结构健康监测、材料表征和生物医学成像。然而，目前的光纤超声发射器的带宽为数十 MHz，这阻碍了细胞上的超声图像分辨率达到 $\mu\text{m}$ 级别。在这里，通过在弯曲的 UV 固化粘合剂波导中使用多模干涉，提出了超紧凑型光纤内超声发射器，该波导是在夹芯偏移拼接光纤段上的两个光纤端面之间制造的。弯曲的粘合剂波导可以将器件反射光谱的对比度从 2.7 dB 提高到 21.7 dB。超声波是由光脉冲激发产生的，通过光吸收和紫外线固化粘合剂的热膨胀，然后通过同一波导的多模干涉与数百 Hz 至 306 MHz 的宽横向声波进行检测。这种超紧凑且具有成本效益的设备为先进的生物医学和基于超声的应用提供了新的机会。