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Varifocal augmented reality adopting electrically tunable uniaxial plane-parallel plates
(2020-07-20)
Wang, Yu-Jen
;
Lin, Yi-Hsin
;
Cakmakci, Ozan
;
Reshetnyak, Victor
;
光電工程學系
Vergence-accommodation conflict (VAC) is a major challenge in optical-see through augmented reality (AR) system. To resolve this conflict, many approaches are proposed, for instance, by means of adjustment of the projected virtual image to coincide with the surroundings, called image registration, which is more often referred to as varifocal function. In this paper, a varifocal AR system is demonstrated by adopting electrically tunable liquid crystal (LC) plane-parallel plates to solve VAC problem. The LC plates provide electrically tunable optical paths when the directors of LC molecules are re-orientated with applied voltages, which leads to a corresponding change of light speed for an extraordinary wave. To provide a sufficient tunable optical path, three pieces of multiple-layered LC structures are used with the total thickness of the active LC layers (similar to 510 mu m). In experiments, the projected virtual image can be adjusted from 1.4 m to 2.1 m away from the AR system, while the thickness of LC plane-parallel plates are only less than 3 mm without any mechanical moving part. When light propagates in the uniaxial LC layers, the wave vector and the Poynting vector are different. The longitudinal displacement of the image plane is determined by Poynting vectors rather than wave vectors. As a result, the analysis of the AR system should be based on Poynting vectors during geometrical optical analysis. Surprisingly, the tunable range of the longitudinal displacement of Poynting vectors is 2-fold larger than the tunable range of the wave vectors. Moreover, the virtual image shifts in opposite directions with respect to the Poynting vectors and wave vectors. The proposed AR system is not only simple but also thin, and it exhibits a large clear aperture. The investigation here paves the way to a simple solution of the VAC problem for augmented reality systems. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Modeling Liquid Crystal Lenses
(2020-01-01)
Reshetnyak, V. Yu.
;
Sova, O.
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Wang, Yu-Jen
;
Lin, Yi-Hsin
;
光電工程學系
Liquid crystal based lenses with variable focal length are of broad interest due to their wide area of applications ranging from techniques to medicine. We present the modeling approaches and results for a couple of tunable liquid crystal based lenses, namely: curved electrode lens, lens with hole patterned electrode and high resistivity layer, lens based on modulated anchoring and contact lens. We also discuss the current challenges associated with the modeling of LC lenses and possible ways to overcome them.
Phase modulators with tunability in wavefronts and optical axes originating from anisotropic molecular tilts under symmetric electric field II: experiments
(2020-03-16)
Wang, Yu-Jen
;
Lin, Yi-Hsin
;
Cakmakci, Ozan
;
Reshetnyak, Victor
;
光電工程學系
We demonstrate, for the first time, an electrically-tunable and physically-planar freeform optical element made up of nematic liquid crystals (LCs). Continued on numerical study in previous paper (Part I), experimental results here show that it is possible to break the rotational symmetry of the wavefront through the use of uneven tilt angles of the LC molecules even though the electric potential is rotationally symmetric. Our optical element offers the ability to electrically tune the direction of the optical axis, the wavefront deviation, as well as the Zernike polynomials for general descriptions of wavefronts. Corresponding Zernike coefficients of a Zernike polynomial that are related to defocus and spherical aberration, which can be adjusted individually or together. The minimum wavefront deviation is >lambda/16. The Zernike coefficients related to coma aberration or the tilt of the optical axis are also electrically tunable. By incorporating our LC phase modulator with tunability of freeform wavefronts into a simple reflective optical system, we demonstrate convincing image performance for off-axis image aberration correction. This approach will inspire further development and design of LC optical elements for applications, such as hyperspectral imagers in aerospace optics, augmented reality, virtual reality, quantum information systems, innovative miniaturized reflective telescopic systems for astrophysics, planetary science, and earth science. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Polarization aberrations of electrically tunable liquid crystal mirrors
(2020-04-13)
Wang, Yu-Jen
;
Lin, Yi-Hsin
;
Cakmakci, Ozan
;
Reshetnyak, Victor
;
光電工程學系
Curved mirrors are able to fold optical paths and play important roles in compact optical systems in general. In this paper, we investigate the polarization aberrations of electrically tunable liquid crystal (LC) mirrors with two kinds of configurations (flat and curved ones). The LC mirrors exhibit spatially-continuous tunable wavefronts. The detailed wavefronts of two LC mirrors are related to angles of incidence, polarization of light, and the alignment direction of LC molecules. The key contribution of this paper is the development and characterization of a tunable liquid crystal mirror. The tunability of polarization aberration of LC mirrors should be able to provide extra parameters for optical engineers to design versatile optical systems. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Electrically tunable gradient-index lenses via nematic liquid crystals with a method of spatially extended phase distribution
(2019-10-28)
Wang, Yu-Jen
;
Hsieh, Huai-An
;
Lin, Yi-Hsin
;
光電工程學系
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Department of Photonics
The dilemma between tunable range of a lens power and an aperture size in gradient-index (GRIN) type of liquid crystal (LC) lenses is well known due to the limitation of birefringence of LC martials and the nature of soft matters. In order to overcome the dilemma of the power law, a multi-layered LC lens was previously proposed by us. However, the aperture size of GRIN LC lenses is still difficult to exceed 10 mm. In this paper, we proposed an electrically tunable GRIN LC lens via nematic liquid crystals with a method of spatially extended phase distribution. A GRIN LC lens with an aperture size of 20 mm is achieved. The proposed GRIN LC lens consists of two LC elements modulating wavefronts at different regions of the lens aperture extending to 20 mm. The lens power of the GRIN LC lens is continuously tunable, while the LC lens can function as a positive lens, a negative lens, and a bifocal lens. The proposed GRIN LC lens not only overcomes the dilemma of the power law but also provides a more practical approach that could benefit the ophthalmic applications and augmented reality systems. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
An optical system for augmented reality with electrically tunable optical zoom function and image registration exploiting liquid crystal lenses
(2019-07-22)
Wang, Yu-Jen
;
Lin, Yi-Hsin
;
光電工程學系
;
Department of Photonics
An optical-see-through augmented reality (AR) system assists our daily work by augmenting our sense with computer-generated information. Two of optical challenges of AR are image registration and vision correction due to fixed optical properties of the optical elements of AR systems. In this paper, we demonstrated an AR system with optical zoom function as well as a function of image registration via two LC lenses in order to help people see better by magnifying the virtual image and adjusting the location of virtual image. The operating principles are introduced, and experiments are performed. The concept demonstrated in this paper could be further extended to other electro-optical devices as long as the devices exhibit the capability of phase modulations. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Liquid crystal beyond displays: feature introduction
(2019-07-22)
Lin, Yi-Hsin
;
Hu, Wei
;
Lin, Tsung-Hsien
;
d'Alessandro, Antonio
;
交大名義發表
The editors introduce the feature issue on liquid crystal beyond displays. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Liquid Crystal Based Terahertz Phase Shifter with Bi-Layer Structure
(2018-01-01)
Sahoo, Anup Kumar
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Yang, Chan-Shan
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Yen, Chun-Ling
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Lin, Hung Chun
;
Wang, Yu-Jen
We propose and demonstrate a liquid crystal (LC) based terahertz phase shifter with a thick (550 mu m in total) bi-layer LC cell structure incorporating a thin transparent polymeric intermediate layer. The present phase shifter exhibited remarkable performance improvement. The phase shift increased from 94 degrees to 111 degrees; threshold and drive voltages decreased from 2.2 V-RMS to 1 V-RMS and from 10 V-RMS to 8.4 V-RMS, respectively, in comparison with those for single-layer cell structure.
Liquid Crystal Based Terahertz Spatial Light Modulator for Imaging Application
(2018-01-01)
Sahoo, Anup Kumar
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Yang, Chan-Shan
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Yen, Chun-Ling
;
Lu, Yuan Chun
;
Lin, Hung Chun
We demonstrate a liquid crystal based THz spatial light modulator (SLM). Indium tin oxide or gold finger type patterns were used for transparent (>70 % at 0.08 to 1.2 THz) conductor and self-cross polarizer. The phase shift and amplitude modulation achieved are greater than 90 degrees and 30 % in broadband in THz frequency. This SLM could become a promising candidate for high speed THz imaging application via compress sensing algorithm
Recent advances in liquid-crystal THz filters
(2018-01-01)
Huang, Chia-Yi
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Chen, Wei-Yuan
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Chiu, Jing-Ya
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Chang, Hsiao-Shan
;
Liu, Jia-Kai
Liquid crystal polymer (LCP) films are rolled into hollow cylinders. The hollow cylinders are measured by a terahertz spectrometer. Experimental results reveal that the transmittance spectra of the hollow cylinders have peaks at specific frequencies due to Fabry-Perot resonance, and the frequencies of the peaks can be tuned by changing the thicknesses and rolled layers of the LCP films. Therefore, the rolled LCP films can be used to develop terahertz filters.

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