Dual-comb absolute distance measurement of non-cooperative targets with a single free-running mode-locked fiber laser

Abstract

We demonstrate dual-comb time-of-flight absolute distance measurement with a free-running dual-wavelength dual-comb mode-locked Er-fiber laser. An anodized aluminum plate with 1.6-μm RMS roughness that locates at a distance of ∼3.46 m serves as a scattering target. The echo has been collected non-coaxially with a 5-inch aperture telescope. The target time-of-flight is acquired by linear optical sampling, which relies on interference between the two combs with spectral overlap. We find that the wavelength of the overlapped spectra determines the fringe density of the interferograms, thus the accuracy of time-of-flight extraction algorithm. The ranging precision is ∼ 10 μm when the collected optical power is ∼1/5000 of that emitted from the launcher. By using Kalman filtering, an improved ranging precision of 225.7 nm has been obtained. The measurement has been conducted at a fixed update rate of 20 Hz, mainly limited by the real-time-based computer data processing speed. Additional measurements of fixed height steps assembled by standard gauge blocks and surface profiling applications have been demonstrated to verify the accuracy of the ranging system. The presented technique is promising for future dual-comb based high precision lidar and remote sensing applications.