Guest editors Yi-Hsin Lin, Victor Reshetnyak, Kai-Han Chang, and Yan Li introduce the Special Section on Micro-optical Systems Based on Liquid Crystals.
The automotive industry recognizes the vibrant development of augmented reality (AR) technology and identifies that it will be a great enhancement for the business from design, manufacturing, safety, and user experience perspectives. Recently, AR head-up displays (HUDs) are showcased with fascinating and useful applications. Several automotive OEMs advertise their intent to implement AR HUDs in future programs. In this presentation, we will focus on HUDs, provide an overview of AR HUD use cases that enhance driver experience, the requirements to create AR experience, and review the enabling technology. Specifically, we will review and describe the key elements of phase holography and the use of this powerful technology to achieve a compact optical system design.
Traditional head-up-displays (HUDs) suffer from a lack of compactness mainly due to the use of bulky optics (i.e., folding mirrors, beam combining optics). The implementation of holographic optical elements (HOEs) in the development of HUDs leads to lighter and more compact units. The aim of this presentation is to demonstrate the use of hologram recording in photo-thermo-refractive (PTR) glass technology for fabricating a diffractive 2D beam splitter for head-up display eye-box. We explored two directions – a combination of transmitting volume Bragg gratings and holographic phase masks encrypted in such Bragg gratings.
Computer-generated holography, a disruptive technology for projection displays, enables variable projection distance by combining a variable lens hologram with an image hologram and encoding it onto a phase-modulating spatial light modulator. The basic structure of a holographic projector includes a spatial light modulator (SLM) to modulate the phase of an incident reconstruction light beam, i.e., a coherent light source (i.e., LASER). Speckle appears in the projected content due to the quasi-random interference of a coherent light source on an optically rough surface that serves as a projection screen. A partially coherent light source, such as a light emitting diode can be used in holographic projection, but image sharpness is sacrificed. Furthermore, due to the limitation of the phase retrieval algorithm, which calculates the hologram to be encoded on the spatial light modulator from a given graphic, the resulting projected content can look speckly due to phase retrieval algorithm imperfections. In this work, we demonstrate reduction in speckle arising from phase retrieval algorithm imperfections through the use of a piston-mode spatial light modulator. The SLM is a two-dimensional micromirror array with extraordinarily fast switching characteristics that enables the implementation of a temporal averaging method for speckle reduction without additional optical components and keeps the benefits of holographic projection.
Laser-based displays suffer from speckle noise due to the random inference patterns of scattered coherent light from rough surfaces. Commonly utilized solution, such as moving diffusers, creates time-varying speckle patterns that were averaged on the observer’s retina or the image sensor. This solution requires the use of motorized parts and can be bulky with the potential risk of mechanical failure. We present a liquid crystal device that reduces speckle noise by over 90%. It is electrically driven, compact, and with no motorized parts. The randomized, time-varying domains with mismatched refractive indices of the liquid crystals produce varying speckle patterns. A near zero speckle contrast is achieved.
We experimentally demonstrate fast flexoelectro-optic switching in a liquid crystal cell containing bimesogen-doped and polymer-stabilized cholesteric. The device exhibits a response time of less than 0.7 ms and with low hysteresis and color dispersion which is suitable for potential applications including field-sequential color displays.
Herein, we report the enhancement of electro-optical performances of nanoparticle embedded liquid-crystal devices in the laser speckle pattern reduction, enhancement of viewing angle, and that of color gamut by doping the nano-particles(NPs) of PγCyclodixtrin-ZrO2 (Shiraishi lab) and Aerosil R-812(EVONIK) into the liquid crystal devices. This report will be done through updating of previous work [1-4] in particular giving physical modeling and simulations.
We demonstrate a liquid crystal Fresnel lens (LCFL) with a surface relief structure which has the binary switching property and the merit of low voltage driving. The surface relief structure is fabricated by photopolymerization of a polymer-precursor initiated by ultra-violet light onto a solid cylindrical Fresnel lens with desired optical power. A liquid crystal (LC) layer is sandwiched between a pair of polymer Fresnel lens deposited with planar alignment layers with orthogonal rubbing directions. The ordinary refractive index of LC is chose to be close to the refractive index of the polymer. At voltage-off state, when the polarization of light is parallel to the long axis of LC molecules, the refractive index mismatch of liquid crystals and polymer Fresnel lens enables the focusing of LCFL. At voltage-on state, the LCFL is a slab with homogenous refractive index because of the index matching between LC and polymer. With the benefit of twisted nematic structure, the voltage requirement is significantly low (~6V) for LCFL. The low-voltage binary beam shaping of laser and magnifying lens function using LCFL are experimentally demonstrated in this paper. Polarization-independent LCFL is achievable with a double-layered approach.
A biosensor for the concentration of high-density lipoprotein (HDL) in human serum on a liquid crystal and polymer composite film (LCPCF) is demonstrated. The sensing mechanism is based on a polar-polar interaction between orientation of LC directors and HDL in human serum. The concentration of polar HDL in human serum affects the orientations of LC directors at the interface between LCPCF and the human serum. In addition, the surface free energy of LCPCF changes with the applied voltage due to the electrically tunable orientations of LC directors anchored among the polymer grains of LCPCF. As a result, the droplet motion of human serum on LCPCF under applied voltages can sense the concentration of HDL in human serum.
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