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.

An improved light field VR display is introduced, featuring an ultra-high-pixel density liquid crystal display with a resolution of 3.1 in. and 1411 PPI. By utilizing a 3K3K resolution display panel, this optimized display enhances the field of view and provides a more immersive experience. Furthermore, it incorporates advanced functions, such as vision correction (without the need for glasses), reduced vergence-accommodation conflict, and an enlarged eye box with eye tracking technology.

We demonstrate the application of liquid crystals to modulate the resonance properties of Yagi-Uda metamaterial absorbers. The absorbance and reflectance peak frequencies and amplitudes were found to be adjustable by reorienting the liquid crystal, irrespective of the polarization of the incident light. Notably, the lowest resonant frequencies were observed when the liquid crystal was in the homeotropic orientation, whereas a reorientation toward the y-axis showed a significant frequency increase, up to 1 GHz. Incorporating liquid crystals to the Yagi-Uda antenna arrays can also serve as a method for eliminating undesired modes, not associated with the antenna resonance. This can be achieved by taking advantage of the sensitivity differences of these modes to refractive index components. The results presented in this study highlight the potential of liquid crystals to deliver dynamic manipulation and real-time adaptability of Yagi-Uda antennas.

A large-aperture liquid crystal (LC) lens with low driving voltage and reduced haze was demonstrated. The root cause of haze owing to orientation fluctuations was discussed. Theoretical and experimental results confirm that the elastic constant and the electric field help to minimize the haze. The haze was reduced 50% after considering the materials and applied electric field. The improved imaging quality and MTF results of the LC lens were also demonstrated. The driving voltage was reduced from 80 V_rms to 18 V_rms by removing the typical buffering layer. The applications of such a LC lens are eyeglasses, head-mounted displays, and near eye displays.

Augmented reality (AR) displays are recognized as an important human–machine interface for next-generation computing platforms. They consist of a micro projector and a waveguide combiner. Researchers are looking for a compact and powerful projector to power up the waveguide combiner. The projector itself is comprised of microdisplays [liquid-crystal-on silicon (LCOS), MicroLED, laser beam scanning, and organic light-emitting diode] that generate the virtual image and a collimating optics module that collimates the image toward the waveguide’s entrance aperture. However, the microdisplays mentioned above suffer from different problems, such as being too bulky, having too low brightness, reliabilities issue, or too high power consumption. In particular, projectors using LCOS are too bulky and heavy to fit into an AR glasses form factor. Therefore, we proposed a new illumination system called front-lit for LCOS. In the front-lit system, the conventional polarization beam splitter (PBS) in the LCOS projector is replaced by a polarized waveguide plate with a micro mirror array. The polarized waveguide functions like a PBS. It reflects the s-polarized beam and transmits to the p-polarized beam. Moreover, the polarized waveguide input beam is shaped to a profile with two intensity peaks from a Lambertian profile by our coupling lens, which is located between the LED and waveguide. Having this profile, the polarized waveguide efficiency is improved, and a larger display illumination area is obtained. From our real measurement results, it is proven that the front-lit LCOS significantly reduces the size and weight of the illumination system. It weighs less than 1 g, and the size of the full module is as small as 0.47cc. The color filter front-lit LCOS and color sequential LCOS deliver 30,000 nits / 175 mW and 100,000 nits / 300 mW, respectively. The color sequential front-lit LCOS also provides high image quality with a 500:1 contrast ratio and 140% sRGB color gamut.

We investigate experimentally the impact of roughly spherular magnetic maghemite (γ-Fe₂O₃) nanoparticles (NPs) on the stabilization of lattices of topological line defects in liquid crystals (LCs). For this purpose, we exploit chiral CE8 LCs, which in bulk exhibit blue phases (BPs) possessing line defects (disclinations) in orientational order. Furthermore, the magnetic NPs stabilize twist-grain boundary A (TGB_A) and chiral line liquid (NL*) phase possessing screw line defects (dislocations) in translational order. Appropriately surface-decorated NPs stabilize these qualitatively different configurations of line defects owing to the defect core replacement and adaptive defect core targeting mechanisms. Magnetic NPs enhance the temperature window of BPI stability and stabilize TGB_A and NL* phases which are absent in bulk LC. Their impact is like the one imposed by strongly geometrically anisotropic NPs, which do not exhibit ferroelectric or ferromagnetic properties.

We proposed a reflowable liquid crystal (LC) geometric phase element for vertical cavity surface emitting laser (VCSEL) projector. By photo alignment technology and LC one drop fill process, we realized an active LC geometric phase element and pattern switchable VCSEL projector. According to geometric phase distribution, the incident light was transformed into different light distribution, such as flood pattern, beam multiplication, or wider illumination. When voltage was applied, all LC directors aligned perpendicularly to substrates and the geometric phase distribution vanished. Therefore, the output light remained as the original projecting pattern. Due to narrow wavelength range of the VCSEL, the optical performance, such as diffraction efficiency and phase difference, was not decayed by the dispersion of geometric phase. We made a record of 3 × 3 mm LC cell with our in-house ink-jet printing system. The transmittance was over 95%, and the switching time was <5 ms.

This work presents a breakthrough in the development of high-resolution virtual reality (VR) displays of 2117-pixels per inch (PPI) liquid crystal displays (LCDs). This technology significantly improves the dynamic range and reduces the screen door effect in VR displays. The challenges and potential solutions for achieving over 2000-PPI LCDs, including the design of the aperture ratio of pixels, improvements in LC efficiency, and overall transmittance, are discussed. Moreover, the use of mini-light-emitting diode backlight and low-power solutions to maintain the image quality in high-resolution designs are also proposed.

We investigated the effects of laser irradiation on sessile droplets of three well-known liquid crystalline materials (5CB, 8CB, E7) deposited on the surface of an iron-doped lithium niobate (LN:Fe) crystal. The static electric field, which is generated via the bulk photovoltaic effect in the LN:Fe substrate, produces the merging of smaller droplets into filaments oriented in the radial direction with respect to the laser spot. It also induces filament jetting from the rim of larger droplets toward the center of the illumination area. When the laser beam is focused directly onto the larger droplets, they abruptly disintegrate via the formation of several jet streams. The described effects are present in the nematic and also in the isotropic phase. We attribute them to a large gradient of the surface electric field that produces driving forces via the induced dipole moments of the droplets, analogous to electric field-based droplets transport mechanisms known for standard dielectric liquids.

A Fourier scatterometry setup is evaluated to recover the key parameters of optical phase gratings. Based on these parameters, systematic errors in the printing process of two-photon polymerization (TPP) gray-scale lithography three-dimensional printers can be compensated, namely tilt and curvature deviations. The proposed setup is significantly cheaper than a confocal microscope, which is usually used to determine calibration parameters for compensation of the TPP printing process. The grating parameters recovered this way are compared to those obtained with a confocal microscope. A clear correlation between confocal and scatterometric measurements is first shown for structures containing either tilt or curvature. The correlation is also shown for structures containing a mixture of tilt and curvature errors (squared Pearson coefficient r² = 0.92). This compensation method is demonstrated on a TPP printer: a diffractive optical element printed with correction parameters obtained from Fourier scatterometry shows a significant reduction in noise as compared to the uncompensated system. This verifies the successful reduction of tilt and curvature errors. Further improvements of the method are proposed, which may enable the measurements to become more precise than confocal measurements in the future, since scatterometry is not affected by the diffraction limit.

Optically pumped magnetometers (OPMs) are becoming common in the realm of biomagnetic measurements. We discuss the development of a prototype zero-field cesium portable OPM and its miniaturized components. Zero-field sensors operate in a very low static magnetic field environment and exploit physical effects in this regime. OPMs of this type are extremely sensitive to small magnetic fields, but they bring specific challenges to component design, material choice, and current routing. The miniaturized cesium atomic vapor cell within this sensor has been produced through integrated microfabrication techniques. The cell must be heated to 120°C for effective sensing, while the sensor external faces must be skin safe ≤40 ° C making it suitable for use in biomagnetic measurements. We demonstrate a heating system that results in a stable outer package temperature of 36°C after 1.5 h of 120°C cell heating. This relatively cool package temperature enables safe operation on human subjects which is particularly important in the use of multi-sensor arrays. Biplanar printed circuit board coils are presented that produce a reliable homogeneous field along three axes, compensating residual fields and occupying only a small volume within the sensor. The performance of the prototype portable sensor is characterized through a measured sensitivity of 90 fT / Hz in the 5 to 20 Hz frequency band and demonstrated through the measurement of a cardiac magnetic signal.