Uncertainty Assessment of Optical Distance Measurements at Micrometer Level Accuracy for Long-Range Applications

We have developed a transportable distance meter based on a 1550 nm laser diode that is intensity modulated at 5 GHz. This fiber-based prototype is realized using telecommunication components that are reliable, largely available and affordable. We have identified and quantified the different sources of error when measuring with this technique a distance between two positions of a same reflector. Minimizing these errors and evaluating their uncertainties lead to a global uncertainty of 4 µm (k=1) up to 1 km. This value does not include the additional errors caused by the evaluation of the atmospheric parameters. This uncertainty has then been verified over 100 m by comparison with an optical interferometer. The prototype was also tested outdoors over 5.4 km and has shown a resolution of 25 µm for an integration time of 10 ms. Distance measurements for long distances with this prototype are still limited by the air refractive index effect. Nevertheless, we have demonstrated that the uncertainty on optical distances reached with this simple technique is compatible with a future development of a two-wavelength system with air index compensation.