High-order phase-shifted Bragg grating waveguide sensor for ultrasound detection

Photoacoustic endoscopy (PE) is an emerging medical imaging technology that combines optical and acoustic imaging modalities, enabling high-resolution imaging of tissues inside the body. Compared to traditional piezoelectric sensors, optical sensors offer advantages in sensitivity, bandwidth, and size, making them suitable for PE applications. This paper demonstrates a high-order phase-shifted Bragg grating waveguide (HP-BGW) fabricated by two-photon polymerization 3D printing as an ultrasonic sensor. The grating is designed to achieve a high transmittance, and sharp line shape in resonant transmission so that enhancing the sensor's sensitivity. The proposed sensor is easy to manufacture and features a wide bandwidth and small size, making it suitable for photoacoustic endoscopy applications. The sensor was characterized using a spectrometer and ultrasound transducers, achieving a Q-factor of approximately 1×10^4 with a bandwidth of around 25MHz and a dynamic range of at least 29MHz.