Edge-lit LCD backlight unit for 2D local dimming

Full-angle chip scale package of mini LEDs with a V-shape packaging structure

The light distribution of light-emitting diodes (LEDs) generally resembles that of a Lambertian light source. When used as large-area light sources, the light distribution angle of LEDs must be modified through secondary optics design to achieve uniformity and minimize the number of light sources. However, secondary optical components pose several challenges such as demanding alignment accuracy, material aging, detachment, and lower reliability. Therefore, this paper proposes a primary optical design approach to achieve full-angle emission in LEDs without the need for lenses. The design employs a flip-chip as the light source and incorporates a V-shaped packaged structure, including a white wall layer, optical structure layers, and a V-shaped diffuse structure. With this design, the LEDs achieve full-angle emission without relying on lenses. Our experimental results demonstrated a peak intensity angle of 77.7°, a 20.3% decrease in the intensity of the central point ratio, and a full width at half maximum (FWHM) of the light distribution of 175.5°. This design is particularly suitable for thin, large-area, and flexible backlight light sources. Moreover, the absence of secondary optical components allows for a thinner light source module.

Zero-optical-distance mini-LED backlight with light-guiding microstructure lens for extra-thin, large-area notebook LCDs

Mini-light-emitting diode (Mini-LED) backlight units (BLUs) in combination with high dynamic range technology can reduce energy and ensure high contrast and luminance. However, the number of LEDs used in mini-LED BLUs is considerably larger than the number of partitions in local dimming, resulting in low cost effectiveness. We proposed a design combining edge-light mini-LEDs and light-guiding microstructure lenses to reduce the number of light sources required in displays considerably. A 16-inch prototype was produced for experiments. The length, width, and thickness of the liquid crystal display module were 351.87, 225.75, and 1.709 mm, respectively. For edge-light mini-LEDs with a pitch of 8.6 mm, the average luminance was 18,836 nits for an input power of 22.5 watts, the uniformity was 85%, the uniformity merit function was 10.13, and the contrast ratio was 60,000:1. Thus, a zero-optical-distance (ZOD) mini-LED backlight for extra-thin, large-area notebook LCDs was produced.

Deep learning-based real-time driving for 3-field sequential color displays with low color breakup and high fidelity

Field sequential color liquid crystal displays (FSC-LCDs) are promising for applications needing high brightness and high resolution because removing color filters brings three times the light efficiency and spatial resolution. In particular, the emerging mini-LED backlight introduces compact volume and high contrast. However, the color breakup severely deteriorates FSC-LCDs. Concerning color breakup, various 4-field driving algorithms have been proposed at the cost of an additional field. In contrast, although 3-field driving is more desired due to fewer fields used, few 3-field methods that can balance image fidelity and color breakup for diverse image content have been proposed. To develop the desired 3-field algorithm, we first derive the backlight signal of one multi-color field using multi-objective optimization (MOO), which achieves a Pareto optimality between color breakup and distortion. Next, considering the slow MOO, the MOO-generated backlight data forms a training set to train a lightweight backlight generation neural network (LBGNN), which can produce a Pareto optimal backlight in real-time (2.3 ms on GeForce RTX 3060). As a result, objective evaluation demonstrates a reduction of 21% in color breakup compared with currently the best algorithm in color breakup suppression. Meantime, the proposed algorithm controls the distortion within the just noticeable difference (JND), successfully addressing the conventional dilemma between color breakup and distortion for 3-field driving. Finally, experiments with subjective evaluation further validate the proposed method by matching the objective evaluation.

Advanced liquid crystal devices for augmented reality and virtual reality displays: principles and applications

Liquid crystal displays (LCDs) and photonic devices play a pivotal role to augmented reality (AR) and virtual reality (VR). The recently emerging high-dynamic-range (HDR) mini-LED backlit LCDs significantly boost the image quality and brightness and reduce the power consumption for VR displays. Such a light engine is particularly attractive for compensating the optical loss of pancake structure to achieve compact and lightweight VR headsets. On the other hand, high-resolution-density, and high-brightness liquid-crystal-on-silicon (LCoS) is a promising image source for the see-through AR displays, especially under high ambient lighting conditions. Meanwhile, the high-speed LCoS spatial light modulators open a new door for holographic displays and focal surface displays. Finally, the ultrathin planar diffractive LC optical elements, such as geometric phase LC grating and lens, have found useful applications in AR and VR for enhancing resolution, widening field-of-view, suppressing chromatic aberrations, creating multiplanes to overcome the vergence-accommodation conflict, and dynamic pupil steering to achieve gaze-matched Maxwellian displays, just to name a few. The operation principles, potential applications, and future challenges of these advanced LC devices will be discussed.

Application of Mini-LEDs with Microlens Arrays and Quantum Dot Film as Extra-Thin, Large-Area, and High-Luminance Backlight

The demand for extra-thin, large-area, and high-luminance flat-panel displays continues to grow, especially for portable displays such as gaming laptops and automotive displays. In this paper, we propose a design that includes a light guide layer with a microstructure above the mini-light-emitting diode light board. The light control microstructure of concave parabel-surface microlens arrays on a light-emitting surface increases the likelihood of total internal reflection occurring and improved the uniformity merit function. We used a 17 in prototype with quantum-dot and optical films to conduct our experiments, which revealed that the thickness of the module was only 1.98 mm. When the input power was 28.34 watts, the uniformity, average luminance, and CIE 1931 color space NTSC of the prototype reached 85%, 17,574 cd/m², and 105.37%, respectively. This module provided a flat light source that was extra thin and had high luminance and uniformity.

Mini-LED Backlight Technology Progress for Liquid Crystal Display

As consumers pursue higher display quality, Mini-LED backlight technology has become the focus of research in the current display field. With its size advantage (100–200 μm), it can achieve one-thousand-level divisional dimming, and it can also be combined with quantum dot technology to greatly improve the contrast, color gamut, dark state and other element of the display performance of LCD displays. Mini-LED backlight technology is undoubtedly the most ideal solution to realize a highly dynamic range display of LCD displays, and has been widely commercialized in many fields such as TVs, tablet computers, notebook computers, and car monitors. This review mainly introduces the efforts made by researchers to eliminate the halo effect, thinning of the backlight module and reducing the backlight power consumption. The application of quantum dot technology in backlight is also presented. We predict that the number of Mini-LED backlight partitions is expected to reach a level of more than 3000 in the future, further utilizing the advantages of the small size in local dimming, but it will also inevitably be challenged by some issues such as power consumption and heat dissipation.

Optimized Micro-Pattern Design and Fabrication of a Light Guide Plate Using Micro-Injection Molding

This study examined the uniformity of illuminance field distributions of light guide plates (LGPs). First, the authors designed microstructural patterns on the surface of an LGP. Then, a mold of the LGP with the optimal microstructural design was fabricated by a photolithography method. Micro-injection molding (μIM) was used to manufacture the molded LGPs. μIM technology can simultaneously manufacture large-sized wedge-shaped LGPs and micro-scale microstructures. Finally, illuminance values of the field distributions of the LGPs with various microstructures were obtained through optical field measurements. This study compared the illuminance field distributions of LGPs with various designs and structures, which included LGPs without and those with microstructure on the primary design and the optimal design. The average illuminance of the LGP with microstructures and the optimal design was roughly 196.1 cd/m². Its average illuminance was 1.3 times that of the LGP without microstructures. This study also discusses illuminance field distributions of LGPs with microstructures that were influenced by various μIM process parameters. The mold temperature was found to be the most important processing parameter affecting the illuminance field distribution of molded LGPs fabricated by μIM. The molded LGP with microstructures and the optimal design had better uniformity than that with microstructures and the primary design and that without microstructures. The uniformity of the LGP with microstructures and the optimal design was roughly 86.4%. Its uniformity was nearly 1.65 times that of the LGP without microstructures. The optimized design and fabrication of LGPs with microstructure exhibited good uniformity of illuminance field distributions.

Thin mini-LED backlight using reflective mirror dots with high luminance uniformity for mobile LCDs

A new mini light-emitting diode (mini-LED) backlight with reflective dots is proposed for high luminance uniformity, high contrast ratio, and low power consumption for use in mobile liquid crystal displays. The proposed backlight, comprising a small number of mini-LEDs, was verified as having high luminance uniformity and high light use efficiency, due to the optimized reflective dots, backlight thickness and light distribution of the mini-LEDs. Moreover, the light leakage to adjacent segments was reduced by cutting a slit between each segment, improving the light use efficiency per segment and suppressing halo artifacts.

Optimal dimension of edge-lit light guide plate based on light conduction analysis

Dimensions of the edge-lit light guide plate (LGP) have a non-negligible impact on its output performance based on a pre-determined micro-dot array. However, how the LGP's dimension affects the performance has not been systematically researched. In this paper, the dimension of the LGP is numerically established as a function to the light output performance, which can be divided into four successive procedures. Firstly, the micro-structural dot array is designed based on the calculated illuminance distribution of the LGP's bottom surface. Based on this, the light energy output can be derived by defining three key parameters, which are dot density, scatting coefficient, and collision loss coefficient. After that, the ray-tracing simulation is used to determine the above parameters. Finally, the optimal dimensions of the LGP can be obtained with a specific correlation function with the light energy output. The mathematical relation above is demonstrated via both simulation and experiment. Our approach provides a systematic design for balancing the efficiency and uniformity of backlight by combining the dot design and the dimensional optimization, which has important theoretical guiding significance for actual display application.

Edge/direct-lit hybrid mini-LED backlight with U-grooved light guiding plates for local dimming

Current mini-LED backlights improve high-dynamic-range liquid crystal displays (LCDs) by using tens of thousands of direct-lit sources for local dimming. However, relative thick profile and high power consumption are the inherent limitations while compared with edge-lit backlights. By synthesizing edge- and direct-lit advantages, we propose a novel hybrid mini-LED backlight equipped with a specially designed integrated light guiding plate (LGP) for large-area displays. This LGP is seamlessly spliced by multiple physically segmented sub-LGPs with a scattering dot array on the bottom and U-shaped grooves at the corners. Each sub-LGP is a single local dimming zone that can be independently controlled. Scattering dot distribution can be numerically calculated even from multiple edge-lit sources. High optical performance and satisfactory local dimming effect are verified and analyzed via both simulation and experiment. The experimental spatial illuminance uniformity and the light extraction efficiency reach 81% and 83% while the crosstalk can be well suppressed below 0.2% between adjacent local dimming zones. The significant advantages of our design towards state-of-the-art mini-LED backlights include the zero optical distance for an ultra-thin profile, low mini-LED amount for local dimming, high optical efficiency, and infinite extension of zone number, which is expected to have a broad application prospect in the near future.

Halo effect in high-dynamic-range mini-LED backlit LCDs

We develop an optical model including the glare effect in the human vision system to analyze the halo effect of high-dynamic-range (HDR) mini-LED backlit liquid crystal displays (LCDs). In our model, an objective function is first introduced to evaluate the severity of the halo effect with different image contents. This function is further combined with PSNR to establish a new evaluation metric to analyze the image quality affected by the halo effect. A subjective visual experiment is also conducted to verify the above-mentioned evaluation metrics. In addition, we analyze the influence of ambient environment (viewing angle and ambient light illuminance) on the halo effect. After considering the requirements on local dimming zones, dynamic contrast ratio, gamma shift, and color shift for practical applications, we find that fringe-field-switching mode is a strong contender for the mini-LED backlit LCD system.