We present sensitive ultrasound sensors with an innovative silicon photonic optomechanical waveguide that features a 15-nm gap between movable parts [Nature Photonics 15, 341 (2021)]. Sensors are fabricated using CMOS-compatible processing and tested for biomedical imaging. @en

Future applications of photo-acoustic imaging require a matrix of small (wavelength/2) and sensitive ultrasound sensors with read-out through a flexible cable. Integrated optical sensors have good prospects: small and sensitive sensors, wafer-scale fabrication, and matrix read-out via single optical fiber using on-chip optical multiplexing. We propose a new type of opto-mechanical ultrasound sensor (OMUS) in silicon photonic chip technology. By using an acoustically resonant membrane in combination with an innovative split rib-type photonic waveguide, we achieve extremely high sensitivity. We present our experimental results in the frequency range up to 30 MHz.@en

Future applications of ultrasound and photoacoustic imaging require a matrix of small and sensitive ultrasound sensors with read-out through a flexible cable. Silicon photonic ultrasound sensors have good prospects: small and sensitive sensors, wafer-scale fabrication, and matrix read-out via single optical fiber using photonic multiplexing. Here, we discuss different types of silicon photonic ultrasound sensors and their applications. This includes our optomechanical ultrasound sensor with extreme sensitivity that is achieved with an innovative optomechanical silicon photonic waveguide in an acoustical membrane. We discuss limitations of state-of-the-art piezoelectric sensors, how silicon photonic sensors overcome these, and applications in medical imaging.@en

We propose a new opto-mechanical ultrasound sensor (OMUS) enabled by an innovative silicon photonics waveguide. We present experimental results up to 30 MHz, a 10-sensor array proof-of-concept and our latest findings.@en

Ultrasonography ¹ and photoacoustic ^2,3 (optoacoustic) tomography have recently seen great advances in hardware and algorithms. However, current high-end systems still use a matrix of piezoelectric sensor elements, and new applications require sensors with high sensitivity, broadband detection, small size and scalability to a fine-pitch matrix. This work demonstrates an ultrasound sensor in silicon photonic technology with extreme sensitivity owing to an innovative optomechanical waveguide. This waveguide has a tiny 15 nm air gap between two movable parts, which we fabricated using new CMOS-compatible processing. The 20 μm small sensor has a noise equivalent pressure below 1.3 mPa Hz ^−1/2 in the measured range of 3–30 MHz, dominated by acoustomechanical noise. This is two orders of magnitude better than for piezoelectric elements of an identical size ⁴. The demonstrated sensor matrix with on-chip photonic multiplexing ^5–7 offers the prospect of miniaturized catheters that have sensor matrices interrogated using just a few optical fibres, unlike piezoelectric sensors that typically use an electrical connection for each element.

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Ultrasonography is widely used in (bio-)medical imaging and especially photo-acoustic imaging is rapidly advancing towards new applications. Future applications require a matrix of small (λ/2) and sensitive ultrasound sensors with read-out through a thin and flexible cable [1]. We target ∼15 MHz ultrasound for e.g. catheter-based intravascular imaging or for freely-moving mouse brain imaging. Integrated optical sensors have good prospects: small and sensitive sensors [2,3], wafer-scale fabrication, and matrix read-out via single optical fiber using on-chip wavelength-division multiplexing (WDM) [4]. Polymer waveguide ring-resonator showed good sensitivity and bandwidth [2] but large device footprint hampers WDM. Silicon photonic waveguides are less susceptible to direct ultrasound but opto-mechanical ultrasound sensors (OMUS), with the photonic resonator integrated in an acoustically resonant membrane, showed high sensitivity [3].

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