Ranging with frequency-shifted feedback lasers: from $\mu$m-range accuracy to MHz-range measurement rate

TL;DR

This paper demonstrates two FSF laser-based ranging systems achieving high accuracy over meters and high measurement rates with moderate accuracy, using frequency measurement techniques that are immune to ambient light interference.

Contribution

It introduces two novel FSF laser configurations for precise and rapid distance measurements, with one system using injection of a phase-modulated laser and the other employing frequency counting without external seeding.

Findings

Ytterbium-fiber system achieves ~1 μm accuracy over meters

Semiconductor system reaches 2 mm accuracy at 1 MHz rate

Both methods are immune to ambient light interference

Abstract

We report results on ranging based on frequency shifted feedback (FSF) lasers with two different implementations: (1) An Ytterbium-fiber system for measurements in an industrial environment with accuracy of the order of 1 $\mu$m, achievable over a distance of the order of meters with potential to reach an accuracy of better than 100 nm; (2) A semiconductor laser system for a high rate of measurements with an accuracy of 2 mm @ 1 MHz or 75 $\mu$m @ 1 kHz and a limit of the accuracy of $\geq $ 10 $\mu$m. In both implementations, the distances information is derived from a frequency measurement. The method is therefore insensitive to detrimental influence of ambient light. For the Ytterbium-fiber system a key feature is the injection of a single frequency laser, phase modulated at variable frequency $\Omega$, into the FSF-laser cavity. The frequency $\Omega_{max}$ at which the detector signal is maximal yields the distance. The semiconductor FSF laser system operates without external injection seeding. In this case the key feature is frequency counting that allows convenient choice of either accuracy or speed of measurements simply by changing the duration of the interval during which the frequency is measured by counting.