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).
DOI: 10.1007/s12200-025-00161-7