Design and fabrication of a micropatterned polydimethylsiloxane (PDMS) light‐guide plate for sheet‐less LCD backlight unit

Abstract— A polydimethylsiloxane (PDMS) light‐guide plate (LGP) having micropatterns with an inverse‐trapezoidal cross section was developed for a sheet‐less LCD backlight unit (BLU). The micropatterned PDMS LGP was fabricated by backside 3‐D diffuser lithography followed by two consecutive PDMS replication processes: photoresist‐to‐PDMS and PDMS‐to‐PDMS replications. The fabricated LGP showed an average luminance of 2878 nits and a uniformity of 73.3% in a 2‐in. backlight module with four side‐view 0.85‐cd LEDs. It also could feasibly be applied to a light source for flexible displays owing to the flexible characteristic of the PDMS itself.     

Modulation of viewing angle on an LCD surface through backlight optics

Abstract— A backlight unit (BLU) that varies the viewing angle from the top to the bottom surface of a transmissive LCD screen has been developed through the design and fabrication of microstructures on a light‐guide plate (LGP). An array of taper prisms has been designed and fabricated on the back surface of the LGP, which resulted in the variation of 29° in the angular distribution of the luminance of the backlight from the top sector to the bottom sector of its surface. This characteristic is employed to modulate the viewing angle of the LCD from the top of the screen to the bottom of the screen for special applications.     

Design and fabrication of the concentric circle light guiding plate for LED-backlight module by MEMS technique

Generally, injection molding technique is applied to fabricate the traditional light guiding plate (LGP). MEMS and hot-embossing techniques applied to fabricate the concentric circle light guiding plate (CCLGP) in this research. The concentric circle v-groove structure and the micro-pyramid structure are constructed on the CCLGP. Therefore, the new backlight module could be simplified to use on only one integrated LGP with any optical components. The CCLGP can eliminate four optical components including the two diffusive sheets and two prism sheets in backlight module, so the space and the fabricated cost of the backlight unit are saved. From the test results, the CCLGP is demonstrated successfully of guide light function and the 82% of illuminative uniformity of the CCLGP is better than the other LGP.     

A monolithic segmented functional light guide for 2‐D dimming LCD backlight

Abstract— An edge‐lit backlight with a thin structure and 2‐D dimming function is a highlighted requirement. To achieve a thin backlight unit for 2‐D dimmable displays, a monolithic functional light‐guide plate (LGP) was segmented by using a recessed U‐groove with graded height as semi‐partitions. The height of the U‐groove controls the cross‐talk between the segments. A single segment was characterized with an array of louver‐shaped micro‐prisms that function as unilateral reflectors for light distributing, directing, and extracting. Arrays of rounded micro‐prisms, and lenticular prisms for in‐ and out‐coupling, are designed on the light injection surface and front surface of the LGP for light‐cone shaping on the BLU. The light guide has a length of 73.0 mm, a width of 40.7 mm, and a thickness of 0.7 mm. The LGP was segmented into 16 segments where the width and graded height of the recessed U‐prism between the segments is 0.020 mm and 0.10–0.50 mm, respectively. By using the monolithic light‐guide plate, the cross‐talk is suppressed to 20% and 4% at the center of first and second neighboring segments, respectively.     

A design of high optical efficiency wedge type light guide plate adopting twin inclined cylindrical surface

We propose wedge type light guide plate (LGP) adopting twin inclined cylindrical surfaces (TICS) at the incident part of a LGP. It has higher optical efficiency than conventional wedge type LGP. In dimension of LGP which the thickness of incident part is 1.5 mm and that of luminance part is 0.7 mm, the optical efficiency of wedge type LGP adopting TICS is expected to be 96% in comparison with a normal flat LGP. In addition, there is an advantage to reduce the non‐uniformity of vicinity of light emitted diodes (LEDs) by TICS reflecting light laterally. However, it is necessary that the LED centers are aligned with the intersections of TICS. The misalignment of LED causes non‐uniformity of optical profile that is slightly larger than a normal LGP.     

The study of integrated LED-backlight plate fabricated by micromachining technique

Generally, a backlight unit (BLU) is considered for the light module of a thin film transistor (TFT) LCD. A typical BLU is comprised of a light guide plate (LGP) and some optical sheets, such as two diffusion sheets, two prism sheets and a reflection sheet. To make the traditional BLU thinner and brighter, we develop an integrated LED-backlight plate (BLP) on microstructures-based, which combine several functions of optical sheets to save the space and fabrication process. The microstructures and the reflective thin film are constructed on the BLP by using micromachining and hot-embossing techniques in the research. From the results of luminous measurements, the luminous uniformity of 86.1% of our fabricated BLP has achieved a demand of a general panel. In future, the micromachining BLP could make the LED-backlight thinner, brighter and lighter for mobile phone applications.     

LED backlight system with double‐prism pattern

Abstract— A LED backlight system with a double‐prism pattern for use in mobile phones to achieve thin and high luminance LED backlight systems is proposed. The double‐prism pattern is formed on the light guide of the proposed LED backlight system and simultaneously exhibited two optical functions: shifting of the light from the direction of the guided light toward the radiated light and controlling the directivity of the radiated light. Therefore, using the double‐prism pattern eliminates two prism sheets and a diffusive sheet, which are indispensable optical elements to exhibit the optical function that controls the directivity of light in conventional LED backlight systems. Consequently, the thickness of the proposed LED backlight system is reduced to 0.75 mm compared to that of the conventional system. A luminance of 3115 nits and a full‐width half maximum of 35° for radiated light, which are comparable to conventional LED backlight systems, were obtained.     

A novel dot‐pattern generation to improve luminance uniformity of LCD backlight

Abstract— This paper reports on a novel theoretical approach to generate irregular dot patterns at the back of the light guide of a backlight unit. By applying this approach to a light guide with a diffuser film, optical distortion is minimized and the luminance uniformity of the backlight is greatly improved.     

Fabrication of cone-like microstructure using UV LIGA-like for light guide plate application

The microlens array is usually formed by thermal reflow of polymer disks and can be one microstructure of the light guide plate (LGP). Here, we propose an ultraviolet (UV) backside exposure technology to fabricate the photoresist cone-like microstructure on the PMMA substrate at room temperature and then use UV LIGA-like process to transfer the microstructure for the application of 3.6 in. (72 mm × 57.5 mm) LGP. The electroforming was used to transfer UV master mold to the inverse cone-like microstructure of nickel metal mold and then hot embossing was used for one more pattern transfer to the same cone-like microstructure on PMMA substrate. The optical microscope and alpha-stepper profiler were used to examine the morphology and profile of LGP microstructure. The optical luminance and uniformity of LGP were measured using BM9 luminance meter in comparison with commercial product. The light uniformity and luminance of the cone-like LGP microstructure reach 75–80% and 2,800–3,000 cd/cm², respectively which meet the requirements of commercial LGP.     

A directional backlight with narrow angular luminance distribution for widening the viewing angle for an LCD with a front‐surface light‐scattering film

Abstract— A directional backlight unit has been developed to widen the viewing angle of a TN‐LCD with a front‐surface light‐scattering film/layer. The novel directional backlight has a diagonal of 34 cm and is structured by light‐direction‐control optical micro‐features and an inverted prism film. The backlight has a symmetrical round luminance cone of ±9° and a uniform spatial distribution of 88%. By using this backlight unit in combination with an LCD, the narrow cone resulted in widening of the TN‐LCD's viewing angle up to 120° at full width at half‐maximum.     

Local dimming light‐guiding plate type backlight system using alignment‐controlled polymer‐dispersed liquid crystals

A new technology which enables a local brightness control according to the displayed images has been expected in the thin and lightweight backlight systems to improve a contrast ratio and power consumption of the liquid crystal displays (LCDs). In this paper, we have proposed a novel local‐dimming backlight system using alignment‐controlled polymer‐dispersed liquid crystals as a light‐guiding plate and investigated the forming conditions of polymer‐dispersed liquid crystals to achieve both a high‐luminance ratio and a fast response speed. As a result, we found that a luminance ratio and response speed of the backlight system can be improved by using bifunctional LC monomer materials and forming fine and rigid polymer network in the LCs, and achieved high luminance ratio of 16:1 and fast response time less than 0.5 ms. In addition, we fabricated the twisted nematic‐mode LCD using the local dimming light‐guiding plate‐type backlight based on this design, and successfully realized eight times higher contrast ratio than that of the traditional twisted nematic‐mode LCD.     

Fabrication of flexible light guide plate using CO2 laser LIGA-like technology

The liquid crystal display (LCD) needs the back light module (BLM) for the light source. The light guide plate (LGP) is the main component of BLM to spread light source to the whole LCD surface and requires for the generation trend of lightweight, easy to carry, and bendable for LCD. In this article, we have demonstrated the fabrication of flexible LGP using CO₂ laser LIGA-like technology which includes the laser ablation of micro-groove polymethylmethacrylate (PMMA) master mold, pouring polydimethylsiloxane (PDMS) to the mold and casting the micro-groove microstructure for flexible LGP application. Different laser powers and micro-groove pitches were used to ablate the PMMA mold with varied groove depths and taper angles. Optical microscope was used to examine the morphology and profile of the final bendable LGP microstructure. Under the varied laser power of 1–12 W, the mean taper angles of PMMA micro-grooves ranged from 28° to 70° and the etching depths were from 44.5 to 281.8 μm. The flexible PDMS LGP had good microstructure duplication after casting. The optical uniformity and luminance of flexible LGP was concerned with structure of micro-grooves and measured using BM9 luminance meter. The maximal light uniformity and average luminance of LGP at some microstructure reaches 75 % and 119 cd/m², respectively.     

Physical‐based photon mapping for an LED backlight lighting simulator

Abstract— Liquid‐crystal displays (LCDs) have become increasingly popular due to their lower price and larger sizes. In particular, backlights having an RGB LED source have recently attracted attention, because they have a wider color gamut, higher luminance, and lower power consumption. However, even when the backlight area is uniformly covered with light modules based on arrays of individual LEDs, this does not ensure a uniform chromaticity and luminance over the backlight panel, thereby stressing the need for lighting simulation of the backlight. Accordingly, this paper proposes an effective lighting simulator to predict the chromaticity and luminance distribution of an LED backlight panel for an LCD. First, the spectrum‐based photons are all initially generated using a random function with a constraint satisfying the spectral power distribution of the actual LED light sources, while their emitting directions are determined based on a pre‐calculated probability using a random variable angle. The optical characteristics of the inner sheets in the LCD backlight structure are then modeled using the wavelength and incident angle to predict the next direction of each photon based on the reflection and transmittance at an intersection. All the photons that reach the unit area of the outward panel are gathered to shape their spectral power distribution, then converted to CIEXYZ values and multiplied with a color‐matching function. Finally, a realistic image visualization of these CIEXYZ values is achieved through standardized device characterization using the sRGB mode. Experiments confirm that the proposed spectrum‐based photon mapping can effectively predict the chromaticity and luminance distribution of an LED backlight panel, providing a good lighting simulation of an LED backlight before manufacturing the LCD.     

Switching directional BLUs for full‐resolution auto‐stereoscopic 3D/2D and 2D/3D LCDs

Directional backlight unit (BLU) design concept was applied to realize full‐resolution field alternate auto‐stereoscopic liquid crystal displays (LCDs) with built‐in 3D/2D and 2D/3D. The application‐oriented BLU design requires priority in realizing 2D mode or 3D mode. The switching characteristic of BLU with two confronting illuminating sets was applied to build 2D mode into 3D display and 3D mode into 2D display. An LCD with 2D mode as primary function requires higher double‐sided luminance uniformity than 3D mode. On the other hand, an LCD with 3D mode requires higher single‐sided luminance uniformity than 2D mode. For increasing the double‐sided luminance uniformity for 2D mode as a primary function of the display, the former BLU design was realized by using uniform prismatic structure, that is, using uniform bilateral prismatic structure with a cross section of isosceles triangle on the back surface of the light‐guide plate. For increasing single‐sided luminance uniformity for 3D mode as a primary function of the display, the latter was realized by using graded angle design, that is, unilateral prisms with a cross section of a scalene triangle on the back surface of the light‐guide plate. The LCDs of small‐sized‐handheld game devices and still cameras were fabricated using the 3D/2D and 2D/3D displays.     

Quantum dots printing paste for display backlights: Preparation,characterization, and applications

Quantum dots (QDs) are one kind of photoluminescent materials with excellent properties, such as adjustable spectrum, narrow full width at half maximum (FWHM), and high color gamut. In this paper, a photoluminescent QDs printing paste suitable for light guide dots array applied in the backlight for liquid crystal display (LCD) was presented. The QDs printing paste was first prepared and characterized with different kinds of solvents. Then, triphenyl phosphite (TPP), a kind of antioxygen, was added into the QDs printing paste to improve the stability of the QDs printing paste. Finally, a QDs light guide plate (LGP) was fabricated by screen printing with QDs printing paste added with silicon dioxide (SiO₂) light scattering particles. The color gamut of QDs LGP arrived 131.6%NTSC due to light scattering interaction between blue LED, red QDs, green QDs, and SiO₂ particles. The results showed that the QDs-chloroform printing paste had uniform light output and the highest photoluminescent peak intensity. Therefore, the composite screen printing paste has wide application prospects in the backlight of LCD, with the advantages of simple process, high production efficiency, and low cost.     

基于改进YOLOv5s的大尺寸导光板缺陷检测

导光板(LGP)是液晶显示器(LCD)背光模组的主要部件. 导光板的缺陷将直接影响液晶显示器的显示效果. 针对导光板图像纹理背景复杂、低对比度、缺陷尺寸小等问题, 本文提出了一种用于大尺寸导光板缺陷检测的AYOLOv5s网络. 首先, 将导光板图像进行分图处理, 然后在主干部分和特征融合部分集成Transformer和注意力机制coordinate attention, 并选择Meta-ACON激活函数. 最后, 基于自建数据集LGPDD进行了大量实验. 实验结果表明, LGP缺陷检测算法的平均精度(mAP)可以达到99.20%, 并且FPS可达77, 可以实现在12 s/pcs内对尺寸为17英寸的导光板中的亮点、划伤、异物、磕碰伤、脏污等缺陷具有较好的实际检测效果.     

Laser marking system for light guide panel using design of experiment and web-based prototyping

A light guide panel (LGP) is an element of the liquid crystal display (LCD) back light unit (BLU), which is used for display devices. In this study, the laser marking process is applied to the fabrication of light guide panels as the new fabrication process. In order to obtain a light guide panel which has high luminance and uniformity, four principal parameters such as power, scanning speed, ratio of line gap, and number of line were selected. A web-based design tool was developed to generate patterns of light guide panel via the network, and the tool may assist the designer to develop various prototype patterns. Topcon-BM7 was used for luminance measurement of each specimen with 100 mm×100 mm area. By Taguchi method, optimized levels of each parameter were found, and luminance of 3523 cd/cm² and uniformity of 92% were achieved using the laser machined BLU.     

How to reduce light leakage and clipping in local‐dimming liquid‐crystal displays

Abstract— In conventional LCDs, the backlight is set to maximum luminance regardless of the image. For dark scenes, this approach causes light leakage and power waste. Especially, light leakage in dark scenes degrades the contrast ratio of LCDs; to circumvent this problem, local‐dimming systems have been proposed. In these systems, the LED backlight is divided into several local blocks and the backlight luminance of each local block is controlled individually, and pixel values are adjusted simultaneously according to the luminance profile of the dimmed backlight. In this paper, a method of determining the LED backlight luminance of each local block depending on the image is proposed; this method significantly improves the image quality of LCDs. First, we introduce methods of quantifying light‐leakage at dark gray levels and clipping at bright gray levels. Then, the proposed method to determine the dimming duty, which controls the LED backlight luminance by compromising between these two measures, was derived. The proposed algorithm preserves the original image with little clipping distortion and effectively reduces light leakage.     

Backlight unit with double‐surface light emission using a single micro‐structured lightguide plate

Abstract— A novel illumination system for a liquid‐crystal‐display (LCD) module used in a dual‐display cellular phone has been developed. A double‐surface light‐emitting backlight uses a single light‐guide plate to illuminate both LCDs. A single lightguide, two prism sheets, and four light‐emitting diodes (LED) were used in the new structure, compared with ten components and two sets of light sources with six LEDs in the current backlight. The thickness and power consumption of the new backlight were reduced by a factor of 0.59 and 0.67, respectively.     

2‐D FOCON arrays and their application in displays and planar illuminators

Abstract— Focusing cones (FOCON) have been designed for fiber‐optic communication systems as coupling devices. The main aim of these couplers is to match the spatial distribution of the light source or photodetector with the aperture configuration of light‐guiding modes of the optical fibers. In this paper, the application of a 2‐D array of FOCONs for collimating large‐sized optical beams in display devices is proposed. The design of a light‐efficient illumination unit for LCDs that can operate in the reflection mode as a backlight has been demonstrated. The approach proposed is based on the spatial separation of the light propagation in a FOCON array for reflected beams and light that comes from the backlight unit. The application of a FOCON array in backlight units and antiglare coatings has been demonstrated.