No abstract

We report on the development of an all-interferometric optomechatronic sensor for the detection of multi-degrees-of-freedom displacements of a remote target. The prototype system exploits the self-mixing technique and consists only of a laser head, equipped with six laser sources, and a suitably designed reflective target. The feasibility of the system was validated experimentally for both single or multi-degrees-of-freedom measurements, thus demonstrating a simple and inexpensive alternative to costly and bulky existing systems.

We present a contactless optical sensor based on the laser-self-mixing effect for real-time measurement of linear and transverse displacements of a moving stage. The sensor is able to measure linear displacements of up to 400 mm along the main optical axis while simultaneously estimating straightness and flatness deviations up to 1 mm. The sensor exploits two identical coplanar nonparallel self-mixing interferometers and requires only one reference plane. The reduction in the number of optical elements allowed by the self-mixing configuration and the intrinsic stiffness of the adopted geometry result in a compact, low-cost, and easy-to-align setup.

We analyze the laser-self-mixing process in the Gaussian beam approximation and reformulate the expression of the feedback coefficient C in terms of the effective feedback power coupled back into the laser diode. Our model predicts a twenty-fold increase of the ratio between the maximum and the minimum measurable displacements judged against the current plane-wave model. By comparing the interaction of collimated or diverging Gaussian laser beams with a plane mirror target, we demonstrate that diverging beams tolerate larger wobbling during the target displacement and allow for measurement of off-axis target rotations up to the beam angular width. A novel method for reconstructing the phase front of the Gaussian beam by self-mixing scanning measurements is also presented.

The behavior of a displacement optical sensor based on the Laser-Self-Mixing effect employing a plane mirror (PT) and a solid corner-cube (CC) as moving target is analyzed. The performance of the sensor is compared in terms of simplification of the optical setup, measurement accuracy and tolerance to angular misalignment of the target. On the basis of the innovative assumption that only the fraction of the laser beam orthogonal to the target plane gives rise to the Self – Mixing modulation, it is demonstrated that the interferometer tolerates small tilt of the plane target (up to approximately 0.7◦) only when illuminated by a divergent beam, in which case the displacement measurement becomes affected by a cosine – type error. Instead the corner cube preserves the self-mixing signal over a larger angular range (up to approximately 2◦) at the same time preserving high measurement accuracy