This paper investigates the use of thin-film optical transmitters to generate focused ultrasound, aiming to develop highamplitude
focused ultrasound. Composite films were used as the optoacoustic sources, which consist of carbonnanotubes
(CNTs) and elastomeric polymers. As the nano-composites work as excellent optical absorbers and efficient
heat converters, thermo-elastic volume deformation within the composites produces strong optoacoustic pressure. These
films were formed on concave substrates for optoacoustic generation of the focused ultrasound. A focal waveform was
measured using a single-mode fiber-optic hydrophone. A peak positive pressure of ~4 MPa was achieved.
Diagnostic ultrasound imaging traditionally uses piezoelectric transducers for transmission and reception of ultrasound
pulses. As the elements in the imaging array are reduced in size, however, the sensitivity will inherently decrease. We
have developed a new, optically-based ultrasound sensor using polymer microring resonators. The device consists of a
100μm-diameter polystyrene ring waveguide coupled to an input/output bus waveguide, and is fabricated by nanoimprint
lithography. Acoustic pressure causes change in the waveguide cross-section dimension and strain in the polystyrene
material, resulting in a change in the effective refractive index and a shift in resonant wavelength. The ultrasonic
waveform can be recovered from this modulation of optical output. The dynamic range and sensitivity of each microring
can be tuned appropriately by adjusting the Q during fabrication. Our experiments show a low noise-equivalent pressure
on the order of 1 kPa. Sensitivity has been measured by the application of known static pressure and a calibrated 20 MHz
ultrasound transducer. A simple 1D array is demonstrated using wavelength multiplexing. The angular response is
determined by sensing the optoacoustic excitation of a 49μm polyester microsphere and shows wide-angle sensitivity,
making the sensors useful for beamforming. The frequency response is relatively flat between DC and 40 MHz, and can
be extended further by choice of substrate material, limited only by the electrical bandwidth of the photodetector. The
high sensitivity, bandwidth, and angular response make it a potentially useful sensor platform for applications in
ultrasound imaging, dosimetry, and non-destructive testing.
Photonic microring resonators have great potential in the application of highly sensitive label-free biosensors and
detection of high-frequency ultrasound due to high Q-factor resonances. Design consideration, device fabrication
techniques, experimental results are report in this paper.