Absolute distance measurement with extended range and rate based on frequency scanning interferometry with a Fabry-Pérot delay line

We present what we believe to be a novel frequency scanning interferometry (FSI) system that integrates a passive Fabry-Pérot (FP) delay line to overcome bandwidth limitations in high-speed, long-range distance metrology. Unlike conventional FSI systems that require high acquisition rates or active switching mechanisms, this architecture utilizes the multiple optical delays within a single FP cavity to produce a comb of modulation frequencies, with a corresponding set of delay surfaces within the measurement volume. The target self-selects the delay surfaces with the lowest modulation frequencies, thus enabling range estimation with low-bandwidth detectors and low-throughput signal processing. Delay order ambiguity is resolved by means of a dual-cavity configuration. Using a swept VCSEL laser (100 kHz repetition rate, 100 nm bandwidth), we demonstrate absolute range measurements up to 1.4 m with sub-3 ppm precision. The maximum sampling rate is a factor of >67× lower than the 54 GS s^-1 required by a conventional FSI system at this range and repetition rate, with a similar reduction in subsequent computational effort. The system is compatible with standard fiber components and scalable to high-speed, real-time metrology applications. It offers a cost-effective, compact solution for dynamic industrial environments where bandwidth, size, and power constraints typically limit FSI adoption.