Optimization of the spatial light modulation with twisted nematic liquid crystals by a genetic algorithm

et al. 2012

Appl. Opt.

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Optical profilometry is widely applied for measuring the morphology of objects by projecting predetermined patterns on them. In this technique, the compact size is one of the interesting issues for practical applications. The generation of pattern by the interference of coherent light sources has a potential to reduce the dimension of the illumination part. Moreover, this method can make fine patterns without projection optics, and the illumination part is free of restriction from the numerical aperture of the projection optics. In this paper, a phase-shifting profilometry is implemented by using a single liquid crystal (LC) cell. The LC phase modulator is designed to generate the interference patterns with several different spatial frequencies by changing selection of the spacing between the micro-pinholes. We manufactured the LC phase modulator and calibrated it by measuring the phase modulation amount depending on an applied voltage. Our optical profilometry using the single LC cell can generate multi-spatial frequency patterns as well as four steps of the phase-shifted patterns. This method can be implemented compactly, and the reconstructed depth profile is obtained without a phase-unwrapping algorithm.

Section: B Calibration Of Lc Phase Modulatormentioning

confidence: 99%

Multi-spatial-frequency and phase-shifting profilometry using a liquid crystal phase modulator

et al. 2012

Appl. Opt.

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“…To enhance measurement accuracy, the discrete Fourier transform method was used for calculating the amount of phase modulation. Therefore, the amount of phase modulation [4] was calculated by…”

Section: Lc Phase Modulatormentioning

confidence: 99%

P‐25: 3‐D Surface Profilometry for Accurate Extraction of Depth Profile with LC Phase Modulator

Noh

Symp Digest of Tech Papers

et al. 2012

We proposed a 3-D surface profilometry with a liquid crystal (LC) phase modulator for accurate extraction of the position and depth profile. The LC phase modulator was designed to develop the dynamic fringe patterns to be operated with multi-spatial frequencies, which were determined by changing the gap between micro-pinholes. The amount of phase shift was controlled by changing the applied voltage. In addition, the fictitious pattern scanning method and geometrical parameters were used to reconstruct position and depth profile of an object. As a result, the depth profile of object could be computed accurately with profilometry. Also, 3-D surface profilometry showed that integrated compact system could be constructed with the proposed scheme.

“…Recently, to obtain color information of an object in addition to the 3D depth information, time-sequential projection of structured and RGB-colored beam patterns was also proposed using fast switching digital light processing (DLP) projectors [22]. However, conventional projection units based on commercial SLMs and DLP are too bulky and not cost-effective for industrial field applications, especially dental imaging, which needs an elaborate and complex semiconductor manufacturing process for the preparation of backplanes to control the 2D phase or intensity patterns with matrix driving schemes [23,24,25]. …”

Section: Introductionmentioning

confidence: 99%

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

Kim

et al. 2016

Sensors

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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.