source: © 2014 Applied Physics Letters
A miniaturized ultrasound sensor is demonstrated in a silicon-on-insulator platform. The sensor is based on a π-phase-shifted Bragg grating formed by waveguide corrugation. Ultrasound detection is performed by monitoring shifts in the resonance frequency of the grating using pulse interferometry. The device is characterized by measuring its response to a wideband acoustic point source generated using the optoacoustic effect. Experimental results show that the sensor’s response is dominated by the formation of surface acoustic waves.
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(a) A schematic, top-view description of the π-WBG (not to scale). w = 500 nm is the waveguide width, Δw = 40 nm is the corrugation depth, L = 250 μm is the length of the grating, and Λ = 320 nm is the period length. (b) A cross-sectional view of the SOI waveguide. (c) An illustration of the fiber coupling to the π-WBG. (d) The transmission spectrum of the connectorized π-WBG device. The inset shows the transmission notch magnified. (e), (f) Schematic drawings depicting the acoustic-characterization experiment for the π-WBG sensor.