Moderate-coherence sensing with optical cavities: ultra-high accuracy meets ultra-high measurement bandwidth and range

Interferometric sensors, renowned for their exceptional accuracy, leverage the wave properties of coherent electromagnetic radiation. The periodicity of the measurement signal often critically limits the measurement range of sensors utilizing interferometry. Here we introduce a cavity-based interferometry concept that capitalizes on a laser with moderate coherence, thereby combining ultra-high accuracy with ultra-high measurement bandwidth and range. To this end mid-fringe detection is combined with measurements of the interferometric visibility. We present experimental results that demonstrate the effectiveness of our approach exemplarily for length sensing. Notably, our system achieves an accuracy of 1 nm with a measurement range of 120 μm (relative uncertainty of 0.00083 %) and a bandwidth ranging from 0 Hz to 20 kHz. These findings support advancements in high-precision sensing applications that demand simultaneous accuracy, measurement range and bandwidth.