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

Interferometric sensors offer exceptional accuracy by exploiting coherent electromagnetic waves, but the periodicity of interference signals critically limits measurement range. This work introduces a cavity-based interferometry concept leveraging a laser with moderate coherence to combine ultra-high accuracy with ultra-high measurement bandwidth and range. By combining mid-fringe detection with measurements of interferometric visibility, the approach breaks the ambiguity of periodic signals. Experimental results for length sensing demonstrate 1 nm accuracy over a 120 µm range (relative uncertainty 0.00083%) and a bandwidth from 0 Hz to 20 kHz. These results enable high-precision sensing applications requiring simultaneous accuracy, wide range, and high-speed operation.