Audio-frequency interferometry at the shot noise limit using an EOIM-based frequency-synthesized light

The shot-noise-limited sensitivity for detecting audio-frequency phase signals has garnered significant interest in both research and practical applications. This work presents a novel experimental setup that generates frequency-synthesized light with suppressed carrier and enhanced sidebands using an electro-optic intensity modulator (EOIM). When injected into a Mach-Zehnder interferometer (MZI), the EOIM-generated light not only enables phase-sensitive heterodyne locking to stabilize the relative phase of the MZI but also functions as a balanced heterodyne detector for audio-frequency phase measurements. By integrating these three key techniques into the MZI, phase detection sensitivity reaches the shot-noise limit across the audio-frequency band. This advancement holds promise for applications in gravitational wave detection, vacuum magnetic birefringence studies, spin-orbital interactions, material characterization, polarization microscopy, atomic magnetometry, and biomedical optics.