Design of an optical refocusing illumination system for use in laser-scanning devices

Optical laser-scanning systems generally contain a scanning lens, like an f-theta lens, to enable a planar imaging field. However, commercially available f-theta lenses show limited working distances and scan fields, while their lens diameter rapidly scales with the scanning range giving rise to bulky lens systems. Therefore, we propose a novel scanning lens configuration, based on a compact tunable lens system, generating a planar imaging field within scanning configurations that require broad scanning fields at large working distances. Particularly, we developed a refocusing illumination lens system, comprising a voltage tunable liquid lens positioned in the centre between 2 passive aspherical lenses. Our novel developed optical system is implementable between the laser source and scanning mirror in a polygon laser-scanning system and ensures a constant spot size along a 640 mm scanning line at a working distance of 900 mm. The voltage tunable liquid lens (Arctic 316 lens of Varioptic) enables to adapt the focal length by the application of a voltage, while the passive aspherical lenses allow to enlarge the working distances and to correct for aberrations. We obtained a compact lens system (system length of 71.8 mm) showing a tunable back focal length between 1078 mm and 1134 mm and 1/e(2) spot diameters between 229 mu m and 238 mu m along the scanning line. Furthermore, we successfully demonstrate the performance of our simulated advanced refocusing illumination system in a laser-based scanning configuration, indicating its potential for integration in industrial scanning systems operating at large working distances while requiring large scanning fields.