# Frequency-modulated continuous-wave laser distance measurement system using Fabry- Perot cavity as measuring reference

## TL;DR

This paper presents a high-precision FMCW laser distance measurement system utilizing a Fabry-Perot cavity as a stable sampling reference, achieving sub-millimeter accuracy over several meters.

## Contribution

It introduces a novel FMCW system with a Fabry-Perot cavity for improved measurement accuracy using Hilbert transform-based resampling.

## Key findings

- Achieved 76.8 μm measurement uncertainty at 6.7 m distance.
- Demonstrated high stability and precision with a 88 GHz laser scan range.
- Validated effectiveness of the frequency-sampling method with F-P cavity.

## Abstract

Frequency-modulated continuous-wave (FMCW) is a ranging technique that allows for high precision distance measurement over long distances. Scanning nonlinearity and range of the tunable laser are the main factors affecting the measurement accuracy. Frequency-sampling method is a recognized post-processing scheme to compensate the scanning nonlinearity. In this work, an FMCW laser distance measurement system using a high fineness Fabry-Perot (F-P) cavity as a sampling reference is demonstrated. The frequency of the resampled signal is calculated with a Hilbert transform. The high stability of the F-P cavity and the advantages of the Hilbert transform lead to a high measurement precision when an external cavity diode laser (ECDL) with a scanning range of tens of GHz is available. In this experiment, the scanning range of the ECDL is only 88 GHz, and a measurement uncertainty of 76.8 um (with coverage factor of k = 2) within a distance of 6.7 m is demonstrated.

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Source: https://tomesphere.com/paper/1901.01131