Echography is an important medical diagnostic technique. Historically, the key improvement driver was the hypothesis that higher image quality leads to better diagnoses and increased patient health. Here, a major parameter is the signal to noise ratio (SNR). Diffraction and attenuation reduce pressure levels during propagation. Thus, an SNR increase yields detection at larger depths benefitting traditionally difficult to image patients (eg large/obese patients). Peak pressures are limited by safety standards (mechanical/thermal index). Thus, to increase SNR more sensitive transducers are required. The state of the art Noise Equivalent Pressure (NEP) for piezotransducers / cMUTs / pMUTs is ~0.5 Pa at 1 MHz [1],[2],[3]. A recent innovation is the Integrated Photonic Ultrasound Transducer (IPUT), which combines a membrane and a photonic waveguide to measure ultrasound waves. Literature [5] reported such a device producing a 0.38 Pa NEP at 0.47 MHz and 21% -6 dB bandwidth with a 169x smaller spatial footprint compared to 0.5 x 0.5 wavelength2. Here, we cascade IPUTs into array elements and transform IPUT sensitivity per area into high absolute sensitivity. Several transducer elements were created by cascading up to 16 IPUTs. After designing these devices, their performance was predicted, and subsequently they were fabricated via VTT’s 3 µm thick silicon-on-insulator (SOI) waveguide platform. IPUT performance was measured in a water tank using a custom calibrated source transducer. The transfer functions and noise of each signal chain component was measured and analyzed. The results showed for a 5 cascaded IPUT element a measured NEP of 4 mPa at 0.54 MHz with a 13% -6 dB bandwidth. This improves on the state-of-the-art by a factor of 90-116x.

Recently there has been a growing interest in sensing by means of optical microring resonators in photonic integrated circuits (PIC) that are fabricated in silicon-on-insulator (SOI) technology. Taillaert et. al. proposed the use of a waveguide based ring resonator as a strain gauge. However, the strong lateral confinement of the light in SOI waveguides and its corresponding modal dispersion was not taken into account. We present experimental results and understanding of the effects of an applied strain in the effective index in a SOI-PIC. In addition, we also investigated the influence of the waveguide geometry.

We present a platform for the deployment of SOI based sensors in commercial
applications. The platform is designed from a systems perspective and includes all
aspects of a SOI sensor system, including sensor head itself, the communications
infrastructure and a customized interrogation system.