Resonant SAW-nanofiber acousto-optic coupling for high-sensitivity detection

We demonstrate an acousto-optic sensing approach that integrates a dual-core As₂Se₃ nanofiber interferometer within a surface acoustic wave (SAW) cavity to achieve externally driven intermodal phase modulation distinct from spontaneous forward Brillouin scattering. Introducing a thin liquid coupling layer allows Rayleigh SAW to satisfy the leaky wave condition causing radiation into the liquid, converting into a leaky SAW, enabling modulation sidebands and narrow detection bandwidths approaching the Hz level. Interferometric sensitivity is improved through coherent detection with balanced receivers and polarization biasing, acting as a common-mode noise rejection system, minimizing the optical noise floor to within ∼1 dB of the photodetector dark-noise limit.