A home-built flexible fiber laser to investigate optimal parameters for stimulating the tympanic membrane

This work investigates optimizing optoacoustic stimulation of tympanic membrane models as a non-occlusive alternative to conventional acoustic drivers. We used a home-built, ytterbium-based master oscillator power amplifier (MOPA) operating at 1064 nm to stimulate an artificial tympanic membrane within a simplified middle ear model. The MOPA system can generate single laser pulses with 200 ps minimum pulse duration as well as concatenating multiple single pulses to MHz-bursts with burst durations up to 100 ns. Burst durations and burst energies were systematically varied between 30 and 100 ns and from 10 to 40 μJ. The laser-induced displacement of the membrane model was measured using phase-sensitive optical coherence tomography. Simultaneously the sound pressure level within a 0.4 ccm volume that mimics the middle ear cavity was measured. The results indicate that the membrane displacement and sound pressure increases both with higher burst energies at the same burst duration and longer burst durations at the same burst energy. Specifically, at a low burst repetition rate of 16 Hz, 100-ns pulse bursts yielded the most efficient stimulation. Furthermore, we demonstrated the system's capability for sound transmission up to 5 kHz by operating the MOPA at a repetition rate of 10 kHz. Using an acousto-optic modulator (AOM) for pulse amplitude modulation, we transmitted a speech signal onto the artificial membrane. The resulting acoustic signal was clearly audible and measurable within the middle ear model. These findings validate the feasibility of using tailored infrared laser pulses for middle ear stimulation. The ability to modulate complex audio signals via flexible, fiber-based laser architecture is a promising approach for developing next-generation hearing restoration technologies that avoid the occlusion effects and discomfort associated with traditional hearing aids.