Optical microcavities have emerged as powerful tools for sensing and imaging, offering advantages over traditional piezoelectric detectors in both sensitivity and bandwidth. Among these, whispering-gallery-mode (WGM) resonators stand out due to their ultrahigh quality factors (Q-factors) and compact size. However, integrating these microcavities into practical, robust devices suitable for real-world environments remains challenging.
A team from Peking University Yangtze Delta Institute of Optoelectronics, led by Dr. Jialve Sun, has now developed a fully packaged WGM microprobe with a Q-factor of up to 2×107. The device uses a side-coupled silica microsphere attached to a U-shaped tapered fiber, encapsulated with a low-refractive-index polymer and capable of operation in both gaseous and liquid media. The microprobe demonstrates a remarkable noise-equivalent pressure (NEP) of 5.4 mPa/√Hz and a broad bandwidth of 41 MHz at –6 dB. It successfully performed photoacoustic imaging (PAI) on various samples, including human hairs, gold patterns, and even an ant, achieving a lateral resolution of ~2 µm. Moreover, the device exhibits ultrahigh-frequency vibrational spectroscopy capability, successfully characterizing the vibrational properties of polystyrene microparticles at 355 MHz.
This innovation opens new possibilities for minimally invasive endoscopic imaging, near-field ultrasound sensing, and vibrational spectroscopy of biological and synthetic microparticles. The robust packaging and high performance make it suitable for use beyond laboratory settings.
The work, entitled " WGM microprobe device for high-sensitivity ultrasound detection and vibration spectrum measurement ", was published in Frontiers of Optoelectronics (published on Aug. 14, 2025).
