Haowen Liang

Optimizing Time-Multiplexing Auto-Stereoscopic Displays With a Genetic Algorithm

A figure-of-merit (FOM) of an auto-stereoscopic display system is introduced and adopted to characterize the system performance. This FOM takes into account of the ratio of the signal to the noise arising from the crosstalk from the adjacent channels as well as the brightness uniformity of viewing areas; hence, it is directly related to the glasses-free 3D viewing comfort. With a steadily improving FOM as a target, the genetic algorithm is applied to optimize the optical system, giving rise to substantially improved characteristics of an auto-stereoscopic display system. The numerical simulation is verified with an experiment of a multi-view auto-stereoscopic display unit. It is shown that the system can provide a high fidelity of the display effect with the crosstalk ratio being reduced from around 5% to nearly 1%, which is a very low value obtainable for an auto-stereoscopic system.

High-quality autostereoscopic display with spatial and sequential hybrid control

A novel design of an autostereoscopic display system with full resolution, low crosstalk, and weak Moiré pattern is presented. The system involves the usage of an LED backlight array and a liquid crystal display (LCD) panel, in conjunction with a Fresnel lens array, to form a 3D optical image system. The finer temporal synchronization is made possible with a dynamic synchronized backlight, so that the scanning of the LCD is in phase with the backlight array. The systematic optimization presents a full HD, or even an ultra HD, display for a single left or right channel. The achieved minimum systematic crosstalk is 2.64%, a sufficiently low value reported so far with an autostereoscopic system.

Full Resolution, Low Crosstalk, and Wide Viewing Angle Auto-Stereoscopic Display With a Hybrid Spatial-Temporal Control Using Free-Form Surface Backlight Unit

A full resolution, low crosstalk and wide viewing angle auto-stereoscopic display is demonstrated with the use of a novel free-form surface backlight (FFSB) technique, in conjunction with a hybrid spatial and temporal control scenario. The overall crosstalk coming from adjacent channels is shown to be lower than 5% even at a wide viewing angle, and minimum achievable crosstalk can be as small as 2.41%. The key element design giving rise to achieving the full viewing angle greater than 45 degrees is also presented.

Quantitative measurement and control of optical Moiré pattern in an autostereoscopic liquid crystal display system

A quantitative description of an optical moiré pattern produced in an autostereoscopic liquid crystal display system is proposed using a contrast sensitivity function. The numerical simulation, carried out in the spatial frequency domain, is applied to a directional backlit, spatially and temporally hybrid controlled display system. The moiré pattern produced from the superimposed binary optical components is examined systematically, and the results show that the visibility of the moiré pattern can be manipulated with proper grating settings. Good agreement between experiment and simulation demonstrates that the proposed theory can be applied as a design guideline to remove the moiré patterns occurring in an autostereoscopic display system.

Enhancing the outcoupling efficiency of quantum dot LEDs with internal nano-scattering pattern.

We report an effective method to extract light from quantum-dot light emitting diodes (QLEDs) by embedding an internal nano-scattering pattern structure. We use finite-difference time-domain method to analyze the light extraction efficiency of red QLEDs with periodic, quasi-random, and random internal nano-scattering pattern structures. Our simulation results indicate that random internal nano-scattering pattern can greatly enhance the outcoupling efficiency while keeping wide viewing angle for the red QLED. Similar results are obtained by extending this approach to green and blue QLEDs. With the proposed red, green, and blue QLEDs combination, we achieve 105.1% Rec. 2020 color gamut in CIE 1976 color space. We demonstrate that internal nano-scattering pattern structures are attractive for display applications, especially for enhancing the outcoupling efficiency of blue QLEDs.

High efficiency quantum dot and organic LEDs with a back-cavity and a high index substrate

We report a back-cavity design to enhance the optical efficiency of a quantum dot light-emitting diode (QLED) or an organic light-emitting diode (OLED) for display and lighting applications. Our simulation results show that the back-cavity design exhibits two major advantages: (1) the transparent electrode helps to increase the transmittance of backward light despite using a semi-transparent metal electrode, and (2) the thickness of the low index optical buffer layer can be optimized to modify the proportion of each optical channel. The proposed back-cavity also helps to lower the refractive index of the high-index substrate from ~2.0 to ~1.8 for achieving high optical efficiency. Finally, the introduced back-cavity does not degrade the color performance of the QLED/OLED.

Simulation and Control of Display Uniformity in a Backlight Illuminated Image Array

The relative retinal illumination (RRI) distribution of a display system consisting of arrayed backlight units, focusing lenses, and viewing screen is simulated with Monte Carlo ray tracing method. A random scattering model is applied to describe the optical seam effect in the vicinity of the stitching. RRI distribution on the screen viewed at different locations for an autostereoscopic display system is simulated, giving rise to a quantitative description of display inhomogeneity on the screen. The method to achieve a uniform RRI distribution on the screen is proposed. The numerical simulation is tested with experimental verification, and good agreement is obtained. The simulation, experiment, and measurement can be applied as design guidelines for autostereoscopic display, integrated imaging display, and other novel backlight illuminated optical systems.

Displaying a full high-definition, high-quality 3D image without glasses

Autostereoscopic displays, which produce an illusion of depth in images without requiring the viewer to wear special glasses, have long been regarded as a desirable improvement to existing 2D display technology for entertainment, industry, and research. Ideally, a 3D viewing system would be compatible with current liquid crystal displays (LCDs). Existing systems include parallax barrier and lenticular techniques, which allow each eye to see different images, creating a sense of depth.1–3 However, these suffer from technical challenges, including reduced resolution, limited viewing angle, and unsatisfactory crosstalk.4 Various approaches have been tried to improve autostereoscopic displays.5–7 Directional backlight solutions are able to preserve full image resolution, but their viewing angles or volumes remain relatively limited. Low crosstalk can also be achieved for a given viewing point, but it remains a challenge to keep it low (less than 5%) across the whole viewing zone. Our display consists of control modules, backlight modules, a lens array, and LCD panel, where the green and blue lightpaths represent light intended for the viewer’s right and left eyes, respectively (see Figure 1). LCDs do not produce light themselves, and thus are illuminated from behind (backlit) by modules consisting of white LEDs. The orientation of the liquid crystals determines whether light from the LEDs is transmitted or blocked by the LCDs, and the orientation is controlled by applying an electric field. An array of Fresnel lenses (compact lenses made up of a series of slanted surfaces) in front of the LCD panel orients the light within the viewing zone. We have used an adaptive optical optimization algorithm to design freeform surface backlight (FFSB) modules and a lens array Figure 1. Top view of the autostereoscopic display system showing the control modules, backlight modules (LED bars made up of an LED array and diffuser), liquid crystal display (LCD) screen, and lens array. (Reproduced from original.8)

Extended depth-resolved imaging through a thin scattering medium with PSF manipulation

Human ability to visualize an image is usually hindered by optical scattering. Recent extensive studies have promoted imaging technique through turbid materials to a reality where color image can be restored behind scattering media in real time. The big challenge now is to recover objects in a large field of view with depth resolving ability. Based on the existing research results, we systematically study the physical relationship between speckles generated from objects at different planes. By manipulating a given single point spread function, depth-resolved imaging through a thin scattering medium can be extended beyond the original depth of field (DOF). Experimental testing of standard scattering media shows that the DOF can be extended up to 5 times and the physical mechanism is depicted. This extended DOF is benefit to 3D imaging through scattering environment, and it is expected to have important applications in science, technology, bio-medical, security and defense.

Ultrahigh Numerical Aperture Metalens at Visible Wavelengths

Subwavelength imaging requires the use of high numerical aperture (NA) lenses together with immersion liquids in order to achieve the highest possible resolution. Following exciting recent developments in metasurfaces that have achieved efficient focusing and novel beam-shaping, the race is on to demonstrate ultrahigh-NA metalenses. The highest NA that has been demonstrated so far is NA = 1.1, achieved with a TiO2 metalens and back-immersion. Here, we introduce and demonstrate a metalens with a high NA and high transmission in the visible range, based on crystalline silicon (c-Si). The higher refractive index of silicon compared to TiO2 allows us to push the NA further. The design uses the geometric phase approach also known as the Pancharatnam-Berry (P-B) phase, and we determine the arrangement of nanobricks using a hybrid optimization algorithm (HOA). We demonstrate a metalens with NA = 0.98 in air, a bandwidth (full width at half-maximum, fwhm) of 274 nm, and a focusing efficiency of 67% at 532 nm wavelength, which is close to the transmission performance of a TiO2 metalens. Moreover, and uniquely so, our metalens can be front-immersed into immersion oil and achieve an ultrahigh NA of 1.48 experimentally and 1.73 theoretically, thereby demonstrating the highest NA of any metalens in the visible regime reported to the best of our knowledge. The fabricating process is fully compatible with microelectronic technology and therefore scalable. We envision the front-immersion design to be beneficial for achieving ultrahigh-NA metalenses as well as immersion metalens doublets, thereby pushing metasurfaces into practical applications such as high resolution, low-cost confocal microscopy and achromatic lenses.