Authors propose a new approach in displacement measurements based on Gaussian beam propagation, their focusing properties and
their spatial modulation. Two modulated Gaussian beams with a phase shift of 180° are focused on a slit fixed to the moveable object.
The resulting laser beams at the slit output are focused into a multimode fiber. A lock-in amplifier demodulates the photodiode signal
placed at the multimode fiber output. The lock in-amplifier output signal is a function of the slit displacement. The sensor is
completely fibered with no electrical wires so it presents no heat dissipation near the moveable object and is compatible with vacuum
use. It is a contactless sensor and provides a simple compact design and cost-effective means of achieving high resolution absolute
displacement measurements. The preliminary experimental data of the sensor calibration by laser interferometry have shown a
resolution of 0.1 nm.
This paper presents a positioning control system based on an optical heterodyne interferometric technique associated to a home-made high frequency electronic board. This system aims to control the translation of a mechanical stage with a quantified step as low as 0.258 574 970 5 (5) nm. Intrinsic relative uncertainty is very low. Hence the method is suitable for long displacement range, even millimeters long. Experimental results show the reliability of the method.