A 3D Optical Surface Profilometer Using a Dual-Frequency Liquid Crystal-Based Dynamic Fringe Pattern Generator

Abstract

We propose a liquid crystal (LC)-based 3D optical surface profilometer that can utilize multiple fringe patterns to extract an enhanced 3D surface depth profile. To avoid the optical phase ambiguity and enhance the 3D depth extraction, 16 interference patterns were generated by the LC-based dynamic fringe pattern generator (DFPG) using four-step phase shifting and four-step spatial frequency varying schemes. The DFPG had one common slit with an electrically controllable birefringence (ECB) LC mode and four switching slits with a twisted nematic LC mode. The spatial frequency of the projected fringe pattern could be controlled by selecting one of the switching slits. In addition, moving fringe patterns were obtainable by applying voltages to the ECB LC layer, which varied the phase difference between the common and the selected switching slits. Notably, the DFPG switching time required to project 16 fringe patterns was minimized by utilizing the dual-frequency modulation of the driving waveform to switch the LC layers. We calculated the phase modulation of the DFPG and reconstructed the depth profile of 3D objects using a discrete Fourier transform method and geometric optical parameters.

Light-Driven Linear Inchworm Motor Based on Liquid Crystal Elastomer Actuators Fabricated with Rubbing Overwriting

“…The dependence of the alignment axis angle on the number of strokes in the first and second (perpendicular) rubbing directions was presented, together with a theoretical model. Authors of [31] described a method involving the unidirectional rubbing of a polyimide coating, which was subsequently partly covered with a mask formed by photolithography. The surface was then rubbed perpendicular to the first rubbing direction and the mask was removed.…”

Development of a Resonant Scanner to Improve the Imaging Rate of Astigmatic Optical Profilometers

“…PTICAL profilometer is widely used for measuring the surface morphology of various materials such as optical components and biomaterials [1]- [3]. Different optical methods, such as focus detection, interferometry, and the astigmatic method, have been employed to realize optical profilometers [4]- [7]. On adopting a commercial digital video disc (DVD) pickup head, an astigmatic optical profilometer provides advantages including compact size, low cost, high resolution, and easy alignment [8]- [10].…”

Magnetic Liquid Switching Using Rodlike Ferronematic 6CHBT Liquid Crystal Mixture Depending on the Diffraction Patterns

“…The diffraction optics were used here for the detection of the intensity change of the diffraction patterns due to the redistribution of patterns affected by the applied magnetic field. The diffraction patterns can be generated by several methods, such as mechanically moving wedge plates [16], tunable gratings [17], switchable gradient index lenses [18], polymer dispersed LC techniques [19,20], phase modulating using spatial light modulator (SLM) [21,22], stretchable binary Fresnel lens [23], and dual-frequency liquid crystal-based dynamic fringe pattern generator (LC-DFPG) [24]. In this work, the diffraction patterns are generated from the micro-lines scribed on the polymer layer that is sandwiched in the LC cell.…”