Perception of sound may be created by irradiating the eardrum with appropriately modulated pulsed light. Such optical stimulation might have several benefits compared to acoustic miniature transducers, including wide-band sound reproduction without the necessity to close the ear canal, and low risk of feedback. Until now, the underlying opto-acoustic transduction mechanisms have not been fully characterized. In turn, it is hard to estimate the limits for equivalent sound pressure generation, or systematically optimize stimulation parameters like the optical wavelength and pulse durations.

We examined several potential transduction mechanisms that are based on expansion of tissue or surrounding air due to light absorption at different structures of the external and middle ear by means of theoretical estimations and experiments. Measurements were conducted in artificial phantoms of the eardrum and middle ear that were tailored to light absorption at specific structures. Measurements included synchronous recordings of sound pressure at both sides of the artificial eardrum, and displacement of the eardrum using phase-sensitive Optical Coherence Tomography in response to nanosecond laser pulses. The results give insights about which transduction mechanisms are dominating and most promising for applications in real ears, and guide the way to a systematic optimization of opto-acoustic stimulation technology.

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