Ultrasound sensing at thermomechanical limits with optomechanical buckled-dome microcavities

Abstract

We describe the use of monolithic, buckled-dome cavities as ultrasound sensors. Patterned delamination within a compressively stressed thin film stack produces high-finesse plano-concave optical resonators with sealed and empty cavity regions. The buckled mirror also functions as a flexible membrane, highly responsive to changes in external pressure. Owing to their efficient opto-acousto-mechanical coupling, thermal-displacement-noise limited sensitivity is achieved at low optical interrogation powers and for modest optical (Q ~ 10^3) and mechanical (Q ~ 10^2) quality factors. We predict and verify broadband (up to ~ 5 MHz), air-coupled ultrasound detection with noise-equivalent pressure (NEP) as low as ~ 30-100 $\mu$Pa/Hz^1/2. This corresponds to an ultrasonic force sensitivity ~ 2 x 10^-13 N/Hz^1/2 and enables the detection of MHz-range signals propagated over distances as large as ~ 20 cm in air. In water, thermal-noise-limited sensitivity is demonstrated over a wide frequency range (up to ~ 30 MHz), with NEP as low as ~ 100-800 $\mu$Pa/Hz^1/2. These cavities exhibit a nearly omnidirectional response, while being ~ 3-4 orders of magnitude more sensitive than piezoelectric devices of similar size. Easily realized as large arrays and naturally suited to direct coupling by free-space beams or optical fibers, they offer significant practical advantages over competing optical devices, and thus could be of interest for several emerging applications in medical and industrial ultrasound imaging.

arXiv comment7 pages, 7 figures

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Cited by in corpus (5)

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• Optical microcavity with a pair of suspended resonant mirrors