Modified functional light‐guide plate for backlighting transmissive LCDs

Abstract— An improved wedge‐type light‐guide plate (LGP) for reducing the light losses and increasing the brightness has been developed. It incorporates a modified design of a molded micro‐line prism array at the rear of the LGP, a molded microdeflector (MD) at the front side of the LGP, and is surrounded by reflectors. The modified LGP employs a single prism sheet. As a result, the brightness is enhanced by 1.56 times compared to that of a conventional LGP and the light rays reaching the back of the LCD is confined to +/?10° on the vertical axis and +/?19° on the horizontal axis.     

Integration of stamper fabrication and design optimization of LCD Light guides using silicon-based microfeatures

This study applies a novel fabrication process that combines anisotropic wet etching of silicon-on-insulator (SOI) wafers with electroforming to manufacture precision stampers. Micron-sized features, such as trapezoidal grooves and truncated pyramidal prisms, can be fabricated and distributed accurately. Because feature geometry and distribution can be accurately realized using the proposed scheme, design optimization of light guide plates (LGPs) becomes realistic. By observing the illumination characteristics of light emitting diode (LED) edge-lit LGPs, the distribution pattern of the LGP is transformed into a parameter design with seven anchor spacing and the spacing modulation amplitude of the micro features adjacent to LEDs. The proposed fuzzy optimization scheme manipulates distribution parameters to obtain an LGP design with high illumination uniformity. The design of a 3.5-inch LED edge-lit LGP is used as an illustrative example. The optical software program TracePro is applied to simulate luminance performance of BLM. The optimization converges rapidly and provides the optimum design with an average brightness of 2,266 (nit) and uniformity of 90% without use of diffusive sheets. Thus work demonstrates the feasibility and effectiveness of the proposed scheme.     

Study on the light delivery to a transmissive‐LCD spatial light modulator used in an LED projector

Abstract— The main targeted areas of this study focused on the optical analysis and design verification of light delivery to a transmissive‐LCD spatial light modulator in LED projectors. The behavior and the distribution pattern of the LED light source, its ray path, and its secondary optical performance in the light tube were investigated. Through the use of LightTools, an optical analysis software, an optical engine structure was established to simulate the LED‐light‐source distribution at the outlet of the light tube after passing through the focus lens. Optical experiments, including a goniophotometer, and scanning illumination measurements were then used to compare the results with computer‐software simulation results to ensure rationality and accuracy of the optical simulation. By using the improved approximation method for uniformity, it was found that the most suitable tilting angle for the light tube would be between 49.2° and 49.4°. The value of the light angle for minimal light intensity deviation to occur was found to be 9°. The optimum location for the light source was found to be 1 mm within the center of the light tube and at 35 mm away from the inlet of the light tube; the effect of uniformity was observed.     

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.     

Design considerations for highly efficient edge‐lit quantum dot displays

Quantum dots (QDs) are increasingly the technology of choice for wide color gamut displays. Two popular options to incorporate QDs into displays include on‐edge and on‐surface solutions. The opto‐mechanical design for an on‐edge QD solution including a LED light bar (“on‐edge QD light bar”) is more complex than the design for a standard white phosphor LED light bar. In this paper, we identify and investigate a range of design parameters for an on‐edge QD light bar, and we show that these parameters have significant influence on system efficiency and color uniformity. The effects of varying these parameters are explored through the use of a custom adjustable testbed and optical raytracing methods. Our testbed data demonstrate the inherent trade‐offs between efficiency and color uniformity and provide guidance for the design of high‐performing displays. The optical raytracing data demonstrate a good predictive capability and support the use of optical modeling methods for a detailed exploration of a wider range of design parameters.     

Electrowetting optical switch with large aperture tuning range

In this paper, we propose an optical switch by deforming the shape of the liquid droplet. The optical switch consists of two immiscible liquids. The dye‐doped water is conductive, while the clear liquid is insulating. In the voltage‐off state, incident light can pass through the circular aperture formed of clear liquid. When the voltage is applied to the liquids, the surrounding dye‐doped water pushes to the side wall because of the effect of electric field force. So, the diameter of the circular aperture is rapidly reduced, and the incident light is absorbed by the dye‐doped water. Our results show that the device can obtain an optical attenuation (~350:1) and reasonable response time (~320 ms). The diameter of the aperture can be largely tuned from ~0.5 to ~6.2 mm as the applied voltage is changed from ~25 to ~65 V. The proposed optical switch has potential applications in light shutters, tunable irises, and variable optical attenuators.     

Holographic backlight unit for mobile LCD devices

Abstract— The commercial backlight unit for a portable liquid‐crystal display (LCD) device typically consists of several light‐emitting diodes (LEDs) as the light source, a couple of prismatic sheets and diffusers, and a guide plate for backlight optics. A simplified backlight unit for portable LCDs, merely consisting of a hologram‐imprinted light‐guide plate (H‐LGP) and one diffuser, is proposed in this paper. By employing H‐LGP, it is expected that several optical films essential to the conventional backlight unit can be eliminated. This paper aims to improve the optical efficiency of LGPs by deriving the design parameters of the H‐LGP and performing the related computations. The angular luminance distribution of the emanating light from H‐LGP has been measured and compared with the results obtained by simulation. A proper collimation is necessary in order to increase the luminance. The backlight developed through this work has high optical performance combined with low cost.     

A novel lens cap designed for the RGB LEDs installed in an ultra‐thin and directly lit backlight unit of large‐sized LCD TVs

Abstract— The objective of this study is to design a novel cone‐shaped lens cap on LEDs in order to achieve high optical efficiency in an ultra‐thin directly lit RGB LED backlight unit (BLU) for large‐sized LCD TVs. The use of the novel lens cap could play the role of a diffuser, a low light‐efficiency component in a BLU, in order to gain higher efficiency and simultaneously provide satisfactory uniformity in light distribution. The novel cone‐shaped lens is coated with aluminum on the outside surface of the cone for mirroring effects to reflect most of the LED emitted light horizontally and then reflect the light at the BLU boundaries, and then, finally to the output plane. In this way, bright spots on the output plane of the BLU can be avoided, leading to increased uniformity. Simulations were conducted to design and optimize varied aspects of the designed lens and BLU, including the cone angle of the proposed lens and the LED spacing (pitch). To further achieve color balance, a known Genetic Algorithm is used to search for the optimal angular placement of each RGB LED, resulting in better color balance. Finally, a prototype BLU for large‐sized 37‐in. LCD TVs with the proposed lens was built to verify the expected performance.     

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.     

The design and optimization of lens array for LED backlight in LCD imaging engine of helmet‐mounted display

The light‐emitting diode has become the mainstream lightsource for backlight in the liquid crystal display imaging engine of helmet‐mounted display. The paper proposes a secondary‐optics‐based design to increase the luminance and obtain a uniform illumination. Based on a point lightsource, a single double‐freeform‐surface lens is firstly designed. Then an optimization is performed according to the theory of edge‐ray to improve the uniformity for planar source. As a result, the uniformity reaches 83.4% in a circular illumination with a diameter of 8 mm. Then the lens is cut and four rectangular lenses are combined to form a lens array. But the combination leads to a non‐uniformity. So a method of optimizing the light energy distribution on the target surface is proposed. Finally, the designed lens array is manufactured. The practical measurement results show that the luminance increases by 96.4% compared with the traditional backlight and that the non‐uniformity slightly decreases by 0.86%. The lens array designed in this paper presents high practicability for applications in helmet‐mounted display.     

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.     

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.     

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.     

Sensorless LED display screen interaction and object recognition

Taking advantage of the photoelectric characteristics of LED other than the light-emitting function, this paper proposes a light sensing detection method and system without adding additional sensors to the LED screen. A two-pole detection structure with a function of detecting positive and negative voltage is introduced to the LED drive circuit, which ensures the high-speed characteristics during detection. What's more, the LED is controlled to work in photoconductive mode to obtain high voltage sensitivity when the intensity of incident light changes. The proposed module can reach an optical signal response rate of 19.1 μs with a detection rate of 23.5 Hz without affecting the original display function. The optical signal detection can reach a voltage sensitivity of 3.02 mV per lx. To verify the photoelectric detection capability of the method presented in this paper, a brand-new screen object recognition system is built and tested. An 8 × 8 LED display module is used in experiment, and the scale of LED screen can be expanded easily and flexibly. In an ideal environment, a recognition accuracy of 99.25% can be achieved, while the recognition accuracy can still reach over 96.5% in a complex light environment. Therefore, this work has further application possibilities for light interaction and fast object recognition in large screens.     

Novel direct‐view LED backlight unit with an aspheric microlens array and a rough‐texture sheet

Abstract— This study proposes a novel direct‐view light‐emitting‐diode (LED) backlight unit with a high‐fill‐factor aspheric microlens array and a rough‐texture sheet. An aspheric microlens array and a rough‐texture sheet made from polysiloxine were used as the grating element and optical diffuser, respectively, which increases light‐extraction efficiency and improves luminance uniformity. The specific aspheric microlens‐array mold was fabricated by using a heating encapsulated air process based on a glass wafer. This microlens array has the features of high fill factor and square‐foot boundary with a continuous surface‐relief profile. This unique out‐of‐plane surface profile creates a square light pattern with uniform luminance, and thus composes a uniform large‐sized light pattern exactly in accordance with the layout of the LED array. The rough‐texture sheet, which can scatter light uniformly, was formed by fine‐grit‐sandpaper molding. Experimental results show that by using an aspheric microlens array and rough‐texture sheet reported here as the backlight diffusing components is highly effective in improving light uniformity at a wide viewing angle. An increase in illuminance by more than 10% was achieved in comparison with commercial backlight modules. Low cost in fabricating the aspheric microlens array and rough‐texture sheet is anticipated due to the simplicity of the process.     

Luminance enhancement without sacrificing the viewing angle in a direct-lit backlight by addressing the angle-dependent characteristic of the prism film

In a conventional backlight, suppression of light loss caused by the prism film(s) is desired to enhance the luminance without sacrificing the viewing angle. In this paper, in a direct-lit light-emitting diode (LED) backlight, where an LED array is placed under the display panel, the transmission efficiency against the prism film(s) is investigated for incident light with different zenith and azimuth incident angles. A strong angle-dependent characteristic is found, even when the reflective recycling effect is available. To address this angle-dependent characteristic in a direct-lit LED backlight, a freeform lens is designed to deflect the light emitted from an LED into the incident angle range with high transmission efficiency. Two design examples are implemented by adopting dual- and single-layer prism film(s). The simulation results show that the freeform lens can enhance the on-axis luminance by 26% and 35%, respectively, while the viewing angle remains nearly unchanged. Furthermore, using a single layer of prism film, a 19-in. direct-lit LED backlight module is constructed for experimental verification. By fabricating the freeform lenses and adding them to the backlight module, the on-axis luminance is enhanced by 24%, and the viewing angle is decreased by no more than 2°. Finally, the influence of the diffusers, which causes the experimental results to degrade slightly compared with the simulation results, is analyzed.     

Optimizing angular placements of the LEDs in a LCD backlight module for maximizing optical efficiency

This study aims to optimize angular placements of the LEDs with novel cone-shaped caps for achieving high optical efficiency in an ultra-thin, directly-lit RGB LED backlight unit (BLU) for large-sized LCD-TVs. This novel lens cap is used as a diffuser with the purpose to gain higher efficiency and provide satisfactory uniformity over a display panel. To this aim, the outer surface of the novel lens is coated with aluminum for mirroring effects to reflect most of the LED emitted light horizontally and then reflect the light at the BLU boundaries, finally to the output plane. Since the emitted white light from LEDs result from color-mixing of three individual RGB chips in a LED package, the addition of the LED cap however deteriorates the aforementioned expected color mixing. The optimal design on angular placements of LEDs presented in this study for satisfactory color-mixing and emission uniformity is achieved by necessary optics simulations via TracePro, followed by utilizing an intelligent numerical optimization technique, genetic algorithm (GA). The design parameters for GA optimization are different combinations of LED placement angles in a backlight module. Favorable color balance is shown achievable in terms of high low color difference resulted. Finally, experiments are conducted, which successfully validate the expected performance of color balance and emission uniformity for a novel cone-shaped LED lens with optimized angular placements in a large-area backlight module.     

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.     

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.     

High-efficiency nanowire light-emitting diodes for augmented reality and virtual reality displays

Through 3D dipole cloud model, RGB (red, green, and blue) nanowire light-emitting diode (LED) structures are geometrically optimized to exhibit a narrower radiation pattern, weaker angular color shift, and higher optical efficiency. In comparison with micro-LEDs whose external quantum efficiency is dependent on the mesa size, these RGB nanowire LEDs are more efficient than micro-LEDs when the chip size is below 20, 80, and 10 μm, respectively. As a result, nanowire LED is a promising candidate for augmented reality and virtual reality displays where high-resolution density and efficient directional light emission are desired.