Photoacoustic tomography defines new challenges for ultrasound detection compared to ultrasonography. To address these challenges, a sensitive, small, scalable, and broadband optomechanical ultrasound sensor (OMUS) has been developed. The OMUS is an on-chip optical ultrasound sensor, using optical interferometric ultrasound detection. It consists of an acoustic membrane on top of an optical ring resonator that modulates the optical ring resonance with high efficiency enabled by an innovative optomechanical waveguide. Raster scanning photoacoustic tomography has been demonstrated with a single-element OMUS. Based on performance and form factor, the OMUS combined with passive optical multiplexing may enable new applications in photoacoustic 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 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].@en

Micro-opto-mechanical Microphone (MOMM) based on integrated optical Mach-Zehnder interferometers (MZI) are promising for future application in medical environments. However, the design of next generation MOMM systems on chip remains challenging due to the intrinsic multi-physics characteristics related to acoustic, mechanical, optical and electrical effects. We therefore developed a methodology composed of acoustic, mechanic, optical, and electronic sections for fast design of high performance MOMM systems. The feasibility has been demonstrated as the operational characteristics of the fabricated MOMM (i.e. resonance frequency, dynamic range, the sensitivity and SNR) align well with the measured references.@en

Micro-opto-mechanical Microphone (MOMM) based on integrated optical Mach-Zehnder interferometers (MZI) are promising for future application in medical environments. However, the design of next generation MOMM systems on chip remains challenging due to the intrinsic multi-physics characteristics related to acoustic, mechanical, optical and electrical effects. We therefore developed a methodology composed of acoustic, mechanic, optical, and electronic sections for fast design of high performance MOMM systems. The feasibility has been demonstrated as the operational characteristics of the fabricated MOMM (i.e. resonance frequency, dynamic range, the sensitivity and SNR) align well with the measured references.@en

This paper presents a new type of accelerometer, the Micro-Opto-Mechanical Accelerometer (MOMA). Micro-opto-mechanical pressure sensors and microphones demonstrated already the excellent sensitivity on a very large pressure range which is possible thanks to their photonic read-out (1Pa precision over kPa range). In this paper, we design in the same technology an optical accelerometer using analytical equations as well as Finite Element simulations. The model takes into account the mechanical deformation of the device, its effect on the elongation of the waveguide, and also includes the optical losses. Using the opto-mechanical model, an optimum design is obtained varying device dimensions and waveguide positions in order to increase the accelerometer sensitivity.@en

Optical ultrasound sensing is a promising technique for the emerging field of biomedical photoacoustic imaging. Previously at imec, micro-opto-mechanical sensors with integrated Mach-Zehnder interferometers were designed and demonstrated as highly sensitive for static pressure sensing. At quasi-static pressures, they are demonstrated to operate as a sensitive microphone. In this study, the application range is extended to include dynamic pressures targeting a proof of concept for a photoacoustic imaging application. To achieve this, the dynamic behavior of the pressure sensor is firstly characterized, showing its resonance frequency at 73.8 kHz. Since this is below the range desired in photoacoustic imaging, several approaches for resonance frequency increase are investigated, resulting positively for incomplete membrane release and new designs. These approaches are analyzed based on the evaluated sensor sensitivity, allowing the selection of optimal design. The mentioned evaluation of sensor sensitivity is possible due to a developed methodology based on measurement data, analytical and accurate acousto-mechanical finite element models. The developed methodology is demonstrated throughout a range of membrane sizes, frequencies and modes of vibration allowing the selection of maximum sensitivity design. In this study, a micro-opto-mechanical ultrasound sensor based on integrated Mach-Zehnder interferometer is designed for 1 MHz operation in a photoacoustic imaging environment and optimized for sensitivity.@en

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