Miniaturization and image optimization of a full-color holographic display system using a vibrating light guide.

In this study, a miniaturized full-color holographic reconstruction system that uses a single spatial light modulator to achieve full-color image reconstruction was developed. The reconstruction system uses a single light guide for light combination and is therefore less voluminous than conventional reconstruction systems. The experimental results demonstrated that the system had a full-color display, corrected light combination, and eliminated zero-order light. The vibrations of the light guide disrupted the temporal coherence of the laser beam, thus ensuring that the speckle in the reconstructed image was almost imperceptible to the human eye.

Polarization-insensitive GaN metalenses at visible wavelengths.

The growth of wide-bandgap materials on patterned substrates has revolutionized the means with which we can improve the light output power of gallium nitride (GaN) light-emitting diodes (LEDs). Conventional patterned structure inspection usually relies on an expensive vacuum-system-required scanning electron microscope (SEM) or optical microscope (OM) with bulky objectives. On the other hand, ultra-thin metasurfaces have been widely used in widespread applications, especially for converging lenses. In this study, we propose newly developed, highly efficient hexagon-resonated elements (HREs) combined with gingerly selected subwavelength periods of the elements for the construction of polarization-insensitive metalenses of high performance. Also, the well-developed fabrication techniques have been employed to realize the high-aspect-ratio metalenses working at three distinct wavelengths of 405, 532, and 633 nm with respective diffraction-limited focusing efficiencies of 93%, 86%, and 92%. The 1951 United States Air Force (USAF) test chart has been chosen to characterize the imaging capability. All of the images formed by the 405-nm-designed metalens show exceptional clear line features, and the smallest resolvable features are lines with widths of 870 nm. To perform the inspection capacity for patterned substrates, for the proof of concept, a commercially available patterned sapphire substrate (PSS) for the growth of the GaN LEDs has been opted and carefully examined by the high-resolution SEM system. With the appropriately chosen metalenses at the desired wavelength, the summits of structures in the PSS can be clearly observed in the images. The PSS imaging qualities taken by the ultra-thin and light-weight metalenses with a numerical aperture (NA) of 0.3 are comparable to those seen by an objective with the NA of 0.4. This work can pioneer semiconductor manufacturing to choose the polarization-insensitive GaN metalenses to inspect the patterned structures instead of using the SEM or the bulky and heavy conventional objectives.

High-performance gallium nitride dielectric metalenses for imaging in the visible.

Metalens is one of the most promising applications for the development of metasurfaces. A wide variety of materials have been applied to metalenses working at certain spectral bands in order to meet the requirements of high efficiency and low-cost fabrication. Among these materials, wide-bandgap gallium nitride (GaN) is one of the most promising materials considering its advantages especially in semiconductor manufacturing. In this work, GaN has been utilized to fabricate the high-performance metalenses operating at visible wavelengths of 405, 532, and 633 nm with efficiencies up to 79%, 84%, and 89%, respectively. The homemade 1951 United State Air Force (UASF) resolution test chart has also been fabricated in order to provide resolvable lines with widths as small as 870 nm. As shown in the experimental results for imaging, the metalens designed at 405 nm can provide extremely high resolution to clearly resolve the smallest lines with the nano-sized widths in the homemade resolution test chart. These extraordinary experimental results come from our successful development in design and fabrication for the metalenses composed of high-aspect-ratio GaN nanoposts with nearly vertical sidewalls.

A Vision toward Ultimate Optical Out-Coupling for Organic Light-Emitting Diode Displays: 3D Pixel Configuration.

Despite stringent power consumption requirements in many applications, over years organic light-emitting diode (OLED) displays still suffer unsatisfactory energy efficiency due to poor light extraction. Approaches have been reported for OLED light out-coupling, but they in general are not applicable for OLED displays due to difficulties in display image quality and fabrication complexity and compatibility. Thus to date, an effective and feasible light extraction technique that can boost efficiencies and yet keep image quality is still lacking and remains a great challenge. Here, a highly effective and scalable extraction-enhancing OLED display pixel structure is proposed based on embedding the OLED inside a three-dimensional reflective concave structure covered with a patterned high-index filler. It can couple as much internal emission as possible into the filler region and then redirect otherwise confined light for out-coupling. Comprehensive multi-scale optical simulation validates that ultimately high light extraction efficiency approaching ≈80% and excellent viewing characteristics are simultaneously achievable with optimized structures using highly transparent top electrodes. This scheme is scalable and wavelength insensitive, and generally applicable to all red, green, and blue pixels in high-resolution full-color displays. Results of this work are believed to shed light on the development of future generations of advanced OLED displays.

Reflective EUVL tool design with generalized Gaussian constant mathematics.

This study aims to develop a systematic design procedure for extreme ultraviolet lithography tools. Through analysis using generalized Gaussian constants, relationships between optical properties and requirements can be obtained, and can be used to help ensure that optical system properties required for the tool are upheld during the design process. As verification of the design method, an eight-mirror 0.4 NA tool design has been demonstrated.

Quantifying scattering coefficient for multiple scattering effect by combining optical coherence tomography with finite-difference time-domain simulation method.

In optical coherence tomography (OCT) systems, to precisely obtain the scattering properties of samples is an essential issue in diagnostic applications. Especially with a higher density turbid medium, the light interferes among the adjacent scatters. Combining an OCT experiment with the finite-difference time-domain simulation method, the multiple scattering effect is shown to affect the scattering properties of medium depending on the interparticle spacing. The far-field scattering phase function of scatters with various diameters was simulated to further analyze the corresponding anisotropy factors, which can be introduced into the extended Huygens-Fresnel theory to find the scattering coefficient of measured samples.

AlGaInP Red LEDs with Hollow Hemispherical Polystyrene Arrays.

A hollow hemispherical polystyrene (HHPS) was fabricated to reduce total internal reflection in AlGaInP-based LEDs. At an injection current of 350 mA, the external quantum efficiencies of LED-I, LED-II, LED-III, and LED-IV are 20.92%, 24.65%, 27.28%, and 33.77% and the wall-plug efficiencies are 17.11%, 20%, 22.5%, and 27.33%, respectively. The enhanced performance is attributed to the light output power enhancement through the surface roughness, microlens-liked PS hemisphere, and scatter-liked HHPS array. In this paper, the rigorous coupled wave analysis (RCWA) numerical method was also conducted to demonstrate the HHPS array effectively enlarge the effective light cone.

Analyses of optical out-coupling of organic light-emitting devices having micromesh indium tin oxide and conducting polymer as composite transparent electrode.

We report the characterization and analyses of organic light-emitting devices (OLEDs) using microstructured composite transparent electrodes consisting of the high-index ITO (indium tin oxide) micromesh and the low-index conducting polymer PEDOT: PSS [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)], that are fabricated by the facile and convenient microsphere lithography and are useful for enhancing light extraction. The rigorous electromagnetic simulation based on the three-dimensional finite-difference time-domain (FDTD) method was conducted to study optical properties and mechanisms in such devices. It provides a different but consistent viewpoint/insight of how this microstructured electrode enhances optical out-coupling of OLEDs, compared to that provided by ray optics simulation in previous works. Both experimental and simulation studies indicate such a microstructured electrode effectively enhances coupling of internal radiation into the substrate, compared to devices with the typical planar ITO electrode. By combining this internal extraction structure and the external extraction scheme (e.g. by attaching extraction lens) to further extract radiation into the substrate, a rather high external quantum efficiency of 46.8% was achieved with green phosphorescent OLEDs, clearly manifesting its high potential.

Efficient speckle-suppressed white light source by micro-vibrated and color-mixing techniques for lighting applications.

In this paper, we have demonstrated an efficient speckle-suppressed white light source generation when a blue laser diode illuminates on a micro-vibrated phosphor paper. Both micro-vibrated and color-mixing techniques are used in this system. With only micro-vibrated technique, the speckle contrast can be reduced from about 50% to 7.4% for the scattering blue image for a 16-ms integration time. Together with color-mixing technique, mixing speckle contrast is defined for laser diode pumped phosphor and almost speckle-free result is achieved. For color temperature lower than 5000 K, almost speckle-free mixed white can be obtained even without vibration technique.

Enhancing Optical Out-Coupling of Organic Light-Emitting Devices with Nanostructured Composite Electrodes Consisting of Indium Tin Oxide Nanomesh and Conducting Polymer.

A nanostructured composite electrode consisting of a high-index indium-tin-oxide nanomesh and low-index high-conductivity conducting polymer effectively enhances coupling of internal radiation of organic light-emitting devices into their substrates. When combining this internal extraction structure and the external extraction scheme, a very high external quantum efficiency of nearly 62% is achieved with a green phosphorescent device.

Laser speckle reduction by phase range limited computer generated hologram in laser projection display system.

The speckle phenomenon is an annoyance in laser projection display systems. We propose a novel speckle suppression method that utilizes the interference concept on a pixel point, which reduces the speckle contrast (SC) of the project image by limiting the phase distribution range in the optical field. The SC formula is derived in the uniform interval phase range for partially developed speckle conditions, showing that the SC can be lowered by lessening the phase range limitation. In the ideal simulation model, the SC can be reduced from 98.77% to 0% as the phase range limitation varies from 2π to 0. The phase range limitation model is a novel method using a computer generated hologram to provide beam shaping and phase limitation. In a more realistic simulation model, the SC is reduced from 99.18% to 16.68%.

Full-frame projection displays using a liquid-crystal-on-silicon spatial light modulator for beam shaping and speckle suppression.

This paper presents a full-frame laser projection display system in which a spatial light modulator (SLM) is used for beam shaping and speckle suppression. Phase-only computer-generated holograms (CGHs) are used to transform a cross section of the incident laser beam into a square nearly the same size as that of the display device. Under different initial conditions, the diffraction patterns generated by the CGHs possess identical intensity distributions but differ with regard to random phase distribution. Image speckles can be suppressed via the temporal addition of diffraction patterns from the CGHs when displayed by the SLM. The addition of 16 speckled images resulted in speckle suppression ratios of 0.290 in simulations and 0.345 under experimental conditions. Not only were the speckles suppressed, but the quality of the overall image was also improved considerably. The proposed approach presents a simple design with low power consumption and stable display architecture for application in pico-projectors.

Front view and panoramic side view videoscope lens system design.

A novel structure of a rigid panoramic endoscope is designed and presented. The inspected target field is imaged on the sensor by an optical lens with a dynamic mechanical module. A microgear and motor are used to drive the dynamic lens components, and a compensation element is used in the system to correct the aberrations due to the protective cylindrical endoscope cover. A long depth of field navigator lens is attached to image the front side. The design details are presented and results are shown.

Efficient speckle reduction for a laser illuminating on a micro-vibrated paper screen.

We have demonstrated an efficient speckle reduction method for laser illumination using a micro-vibrated paper screen along the projection direction. Using this method, a micro-vibrated amplitude of 0.532 µm, or a 2π phase change is sufficient to de-correlate the generated speckle pattern for a static SHG green laser beam image. When the measured speckle contrast is lowered to about 5.0%, and comparable with an LED source, a speckle-free image can be achieved. This technique will be suitable for compact and portable laser illumination equipment, image display, signal sensing devices, and so forth. Wearable and near-to-eye laser display applications are also included.

Plasmonic ITO-free polymer solar cell.

The aluminum and sliver multilayered nano-grating structure is fabricated by laser interference lithography and the intervals between nanoslits is filled with modified PEDOT:PSS. The grating structured transparent electrode functions as the anti-reflection layer which not only decreases the reflected light but also increases the absorption of the active layer. The performances of P3HT:PC61BM solar cells are studied experimentally and theoretically in detail. The field intensities of the transverse magnetic (TM) and transverse electrical (TE) waves distributed in the active layer are simulated by rigorous coupled wave analysis (RCWA). The power conversion efficiency of the plasmonic ITO-free polymer solar cell can reach 3.64% which is higher than ITO based polymer solar cell with efficiency of 3.45%.

Design and fabrication of birefringent nano-grating structure for circularly polarized light emission.

Three different nano-grating structures are designed as phase retarders that can transform linearly polarized light to circularly polarized emission for the wavelengths of 488 nm, 532 nm and 632.8 nm, respectively. Gold based nano-grating structures with various periods are fabricated by utilizing laser interference lithography. The ellipticity of all circularly polarized emission can reach around 90% such that the structure has great potential in the applications of three-dimensional (3D) display. The effects of the slit width and metal thickness modulations are simulated by rigorous coupled wave analysis (RCWA) method. Besides, the field intensity and phase of the transmitted TM and TE waves are also simulated to understand their polarization characteristics.

Investigation of designated eye position and viewing zone for a two-view autostereoscopic display.

Designated eye position (DEP) and viewing zone (VZ) are important optical parameters for designing a two-view autostereoscopic display. Although much research has been done to date, little empirical evidence has been found to establish a direct relationship between design and measurement. More rigorous studies and verifications to investigate DEP and to ascertain the VZ criterion will be valuable. We propose evaluation metrics based on equivalent luminance (EL) and binocular luminance (BL) to figure out DEP and VZ for a two-view autostereoscopic display. Simulation and experimental results prove that our proposed evaluation metrics can be used to find the DEP and VZ accurately.

Effects of the spatial frequency composition of the target pattern and the number of quantization levels in diffractive beam shaper design.

A mathematical model is derived, and numerical simulation is analyzed for laser beam shaping by using multilevel phase-only diffractive optical elements (DOEs). We used the simulated annealing algorithm to design the beam shapers. The result has an essential effect on the diffractive pattern quality caused by the spatial frequency composition of target patterns for the same incident gaussian beam size and target pattern area. The root mean square error between the diffractive and target patterns is smaller for the target patterns with lower spatial frequencies. Moreover, the effect of spatial frequency composition can be relaxed for the cases of larger incident gaussian beam size. In addition, finer quality control of a diffraction pattern can be obtained by increasing the number of quantization levels at the DOEs.

Ultra-wide-view patterned polarizer type stereoscopic LCDs using patterned alignment.

The proposed patterned polarizer rather than the conventional ±λ/4 polarizer can further reduce the crosstalk through its corresponding glass for stereoscopic LCDs and can be fabricated by using the same patterned alignment technique. The patterned polarizer comprises a linear polarizer, a patterned retarder and a biaxial film. The maximum crosstalk ratio of the optimal design is reduced from 0.1 (for the conventional circular polarizer using ±λ/4 retarder and positive C film) to 0.016 (for the proposed structure) at ±60° viewing cone for the light obliquely passing through both the glasses and the LCD at the same angle. As to the light normally passing through both the LCD and glasses, the maximum crosstalk ratio can be reduced from 0.0167 to 0.0126 with rotated glasses.

Design of polarization-insensitive multi-electrode GRIN lens with a blue-phase liquid crystal.

We report the design and simulation results of an adaptive GRIN lens based on multi-electrode addressed blue phase liquid crystal. A high dielectric constant layer helps to smoothen out the horizontal electric field and reduce the operating voltage. Such a GRIN lens is insensitive to polarization while keeping parabolic phase profile as the focal length changes.