Simple liquid crystal display backlight unit comprising only a single-sheet micropatterned polydimethylsiloxane (PDMS) light-guide plate

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.

Friction and Wear Characteristics of Polydimethylsiloxane under Water-Based Lubrication Conditions

In this study, the friction and wear characteristics of polydimethylsiloxane (PDMS) were evaluated when using lubricants created by adding surfactants at various ratios to deionized (DI) water. When pure DI water is used as a lubricant, the repulsion of water from the hydrophobic PDMS surface is large and the interfacial affinity is low; thus, the lubrication properties cannot be significantly improved. However, when a lubricant with a surfactant is added to DI water, the interfacial affinity with the PDMS surface increases to form a lubricating film, and the friction coefficient is greatly reduced. In this study, under dry and pure DI water conditions, severe wear tracks were formed on the PDMS surface after 10,000 cycles of reciprocating sliding motion under a vertical load of 100 mN, whereas in the case of the surfactant-based and water-based lubricant, no severe wear tracks occurred. The friction and wear characteristics of the PDMS were evaluated by increasing the normal loads and sliding cycles with a water-based lubricant containing 1 wt % surfactant. Under normal loads of 300 mN and 500 mN, only minor scratches occurred on the PDMS surface up to 10,000 and 100,000 cycles, respectively, but after 300,000 cycles, very severe pit wear tracks occurred.

Effect of Glass Bubbles on Friction and Wear Characteristics of PDMS-Based Composites

The purpose of this study is to improve the mechanical durability and surface frictional characteristics of polymer/ceramic-based composite materials. Polydimethylsiloxane (PDMS)/glass bubble (GB) composite specimens are prepared at various weight ratios (PDMS:GB) by varying the amount of micro-sized GBs added to the PDMS. The surface, mechanical, and tribological characteristics of the PDMS/GB composites are evaluated according to the added ratios of GBs. The changes in internal stress according to the indentation depth after contacting with a steel ball tip to the bare PDMS and PDMS/GB composites having different GB densities are compared through finite element analysis simulation. The elastic modulus is proportional to the GB content, while the friction coefficient generally decreases as the GB content increases. A smaller amount of GB in the PDMS/GB composite results in more surface damage than the bare PDMS, but a significant reduction in wear rate is achieved when the ratio of PDMS:GB is greater than 100:5.

Analytic design of light extraction array for light guide plate based on extended sources

Light extraction array, comprised of millions of discrete scattering dots randomly distributed on edge-lit light guide plates (LGPs), determines both the light efficiency and spatial uniformity of liquid crystal displays. However, it is hard to define by a specific mathematical expression. Here, we propose a novel analytic design for light extraction array based on geometrical optical principles. This design method consists of three successive procedures evolving from point- and line-source approximations to extended surface-source computation. Three procedures are demonstrated via both simulation and experiment, and the key factors influencing the performance of the light extraction array are also discussed. Our approach with high accuracy and reduced complexity will have broad prospect for illumination design.

Improvement of the microprism distribution expression of an integrated light guide plate

In our lab, the coefficient relational expressions called A(L,H), B(L,H), and C(L,H) between the coefficients in the microprism distribution expression and the structural parameters of the integrated light guide plate, which is to realize high luminance uniformity, have been proposed previously. Yet, there are some deficiencies in these coefficient relational expressions, such as numerical item redundancy and inconspicuous physical characterization. On this basis, the revised coefficient relational expressions of A(L,H), B(L,H), and C(L,H) are further studied. As a result, the numerical items of A(L,H), B(L,H), and C(L,H) are reduced by one-quarter, one-third, and one-half, respectively. The redundant high-order items are reduced, and C(L,H) is no longer a piecewise function. After revision, the effect of each numerical item on the coefficient values is highlighted, and it makes the physical characterization of each numerical term clearer. Moreover, by applying the revised coefficient relational expressions to acquire the microprism distribution, the luminance uniformities of all designed integrated backlight modules of 7.0 in. or less in size are totally higher than 85%. Taking a 5.0 in. integrated backlight module as an example, the performance of the integrated backlight module designed by the revised coefficient relational expressions is also improved over that before the revision. It verifies the correctness, effectiveness, and universality of the revised coefficient relational expressions, which will save a lot of design time.

Tilted light coupling structure for the thickness reduction of a liquid crystal display backlight

It is hard to design a traditional edge-lit light guide plate (LGP) as an ultrathin structure, because the LGP thickness will be limited by the luminescence regional width of the LED source. In this paper, a tilted light coupling structure (TLCS) for a liquid crystal display (LCD) backlight is proposed that allows an inclined layout of an edge LED array to significantly reduce the LGP thickness. The design process and optical conditions of the TLCS are first discussed, and the effect of structural parameters on the coupling efficiency is also analyzed. After that, a fundamental model and an improved model are designed: namely, the planar TLCS and the curved TLCS. Design results show that the light coupling efficiency of the proposed TLCS can reach 95%, while the LGP thickness is reduced to 7% thinner than the luminescence regional width of the LED source. The proposed TLCS will have broad applications in light guiding devices.

Microstructured light guiding plate for single-sided light emission as light source for room illumination

Microstructured light guiding plates (LGP) open up new capabilities in the design of energy efficient and flexible light sources for room lighting. One desirable application is the illumination of office rooms by LGPs located mainly at the façade. Starting with the requirements of an ideal light distribution curve for uniform room lighting, suitable optical microstructures have been designed and investigated by numerical ray tracing methods to be integrated in façade elements. The maximum of the desired light distribution curve for the test case is at an angle of 96° with respect to the vertical direction. The designed micro-system meets this requirement very well at an angle of 98° and a light cone width of 25°. The light emission of the proposed LGP is highly efficient with 80% coupling efficiency.

Edge-lit LCD backlight unit for 2D local dimming

Local dimming technology has been highly desired for integration with liquid crystal displays (LCDs) in order to improve their contrast ratios (CRs) as well as to overcome power efficiency bottlenecks. In this paper, we propose and demonstrate a slim (~1 mm) edge-lit LCD backlight unit (BLU) capable of 2D local dimming. We designed a semi-partitioned light guide plate (LGP) patterned with inverse-trapezoidal microstructures, which allows the ultra-slim BLU to function without prism sheets. Since light emitting diodes (LEDs) are placed in the middle of the LGP, the BLU can freely define illuminated areas and the whole BLU can be modularly expanded like a tile canvas. The fabricated BLU achieves uniformity in both local and global luminance distributions, as well as in high local dimming performance. Experimentally, the BLU increases the CR of the display up to two orders of magnitude compared to conventional BLUs.

Integrated backlight module to provide a collimated and uniform planar light source

We report a novel integrated backlight module (IBLM), which is composed of a compound optical film (COF) and a light guide plate (LGP) without any microstructure. The COF proposed in the paper comprises functions of a conventional microstructure that adjusts the emergent light and two cross brightness enhancement films (BEF). The four surfaces of the LGP are coated with highly reflective film. The COF can not only adjust the distribution of the output light by varying the density of the microstructure on the COF, but also can collimate the two cross-direction lights into the normal direction. The horizontal and vertical full width at half maxima of angular intensity of the IBLM with the proposed COF for the optimum are of 14 and 24 deg, respectively. The spatial uniformity and total optical efficiency of the IBLM have reached 85% and 77.2%, respectively. The optical efficiency has been increased by 1.3 times and the on-axis luminance has improved by 5.1 times by using a backlight module (BLM) with the COF, in comparison with the conventional edge-lit BLM that we researched [Appl. Opt.55, 1494 (2016)APOPAI0003-693510.1364/AO.55.001494]. Most importantly, the COF only needs to be configured with a relatively low-cost and easily-manufactured LGP; therefore, the BLM with the adopted COF can be further developed for large-sized application.

Liquid biopsy and therapeutic response: Circulating tumor cell cultures for evaluation of anticancer treatment

The lack of a robust anticancer drug screening system to monitor patients during treatment delays realization of personalized treatment. We demonstrate an efficient approach to evaluate drug response using patient-derived circulating tumor cell (CTC) cultures obtained from liquid biopsy. Custom microfabricated tapered microwells were integrated with microfluidics to allow robust formation of CTC clusters without pre-enrichment and subsequent drug screening in situ. Rapid feedback after 2 weeks promotes immediate intervention upon detection of drug resistance or tolerance. The procedure was clinically validated with blood samples (n = 73) from 55 patients with early-stage, newly diagnosed, locally advanced, or refractory metastatic breast cancer. Twenty-four of these samples were used for drug evaluation. Cluster formation potential correlated inversely with increased drug concentration and therapeutic treatment. This new and robust liquid biopsy technique can potentially evaluate patient prognosis with CTC clusters during treatment and provide a noninvasive and inexpensive assessment that can guide drug discovery development or therapeutic choices for personalized treatment.

Dual-view angle backlight module design

We propose a bilayer light guide plate (BLGP) with specially designed microstructures and two light source modules to achieve an adjustable viewing angle backlight for ecofriendly displays. The dual viewing angle backlight module has a thin, simple structure and a high optical efficiency. Comparison with the conventional edge-lit backlight module shows an improvement in the on-axis luminance of the narrow viewing angle mode of 4.3 times and a decrease in the half-luminance angle of 7° in the horizontal direction. When using the wide viewing angle mode, there is an improvement in the on-axis luminance of 1.8 times and an improvement in the half-luminance angle of 54° in the horizontal direction. The uniformity of illuminance can reach 80% in each mode. The backlight optical sheet number is reduced from 5 to 1.

Novel buried inverse-trapezoidal micropattern for dual-sided light extracting backlight unit

We devised a novel buried inverse-trapezoidal (BIT) micropattern that can enable light extracting to both front and back sides of the backlight unit (BLU). The proposed BLU comprised of only a single-sheet light-guide plate (LGP) having the BIT micropatterns only on the top surface of the LGP. The proposed BLU shows normal directional light emitting characteristics to both the front and back sides of the LGP and successfully acts as a planer light source for a dual-sided LCD. The proposed BLU has the potential to dramatically reduce the thickness, weight and cost of the dual-sided LCD thanks to its single-sheet nature.

Asymmetric optical microstructures driven by geometry-guided resist reflow

We report a new method, termed geometry-guided resist reflow, for the batch fabrication of asymmetric optical microstructures. Thermoplastic microstructures reflow along the geometric boundaries of the adjacent thermoset microstructures above the glass transition temperature of thermoplastic resin. The shape profiles can be freely formed as a concave, convex, or linear shape and the slope angle can also be tuned from 7 to 68 degrees, depending on the geometric parameters. This new method provides a new route for developing functional optical elements.

Algorithm research on microstructure distribution on the bottom surface of an integrated micro-optical light guide plate

Based on the backlight module (BLM) with an integrated micro-optical light guide plate (MOLGP) that we proposed [Opt. Express21, 20159 (2013)], an optical model that maps the relationship between the distribution of microprisms on the bottom surface of the integrated MOLGP and the luminance of the output light is established by a backpropagation neural network in this paper. Then the optimized distribution of the microprisms for high luminance uniformity of the output light is obtained by a genetic algorithm. Finally, the integrated BLM with the optimized distribution of microprisms on the bottom surface of the integrated MOLGP is set up in optical software, and the simulation results show that the luminance uniformity of the output light in this BLM reaches 93%.

A slim apparatus of transferring discrete LEDs' light into an ultra-collimated planar light source

In this paper, we proposed a novel apparatus, which has very slim volume and can transfer light emitted from discrete LEDs into a uniform and ultra-collimated planar light source (UCPLS). This apparatus adopts the two-layer folded frame and two-stage CPC design so that thickness of the entire apparatus can be minimized; especially the feeder in the two-stage CPC design can greatly reduce the thickness of the CPC and make the light passing through the second-stage CPC become much more collimated. In addition, by side-by-side arrangement, a large-sized UCPLS can also be obtained. In our embodiment with an emitting area of the upper LGP of 280 mmX80 mm and a LED with optical flux of 8 lumens used as the light source, the performance according to the related simulation results shows as follows: angular FWHM of the resultant light emitted from the apparatus in the vertical and horizontal is 4.87 degrees and 24 degrees, respectively; spatial uniformity and total energy efficiency reach 84% and 69%, respectively; the average head-on luminance reaches up 5600 nit, yet this apparatus consumes just 60 mW. Furthermore, the results also demonstrate this design has potential to be applied to the product of 23 inches above while thickness of the entire apparatus is only 2.2 mm.

A novel optical film to provide a highly collimated planar light source

In this paper, we proposed a novel optical film 'Collimation Film with Equivalent Focal Reflective Aperture' (CFEFRA) that can collocate with the proper light guide plate (LGP) to provide a highly collimated planar light source (HCPLS) that not only has high intensity peak but also good uniformity. The CFEFRA has micro-cylindrical lenses and inverted-prism-like micro-teeth on its upper surface and lower surface, respectively. The lower micro-teeth that are aligned with the upper lenses can deflect the light emitting from the LGP at large declination into the normal, and then the deflected light with transverse fan-out is further converged by the upper lens to become the collimated light. The exact alignment between the upper and lower micro-structures is fulfilled by the method 'auto-secure-alignment by focusing of a collimated exposure beam'. The vertical and horizontal full width at half maximum (FWHM) of angular intensity of the HCPLS for the optimal case are of 14 and 6 degrees, respectively. Moreover, it still has high optical efficiency with light output of over 90% despite the resultant emitting light is such collimated. Most importantly, CFEFRA just needs to collocate with a relatively low-cost and easily-manufactured LGP so the HCPLS adopting the CFEFRA can be extended for large-sized application. Both optical model and experimental samples are demonstrated in this paper, and the simulation results are consistent with the experimental results. The consistency proves our design concept and optical model are convincible and feasible.

Integrated micro-optical light guide plate

In this paper, we propose an integrated micro-optical light guide plate (MOLGP), of which the top surface is designed as aspheric semi-cylindrical micro-concentrator structure (ASCMCS) arrays and the bottom surface is fused with micro-prism arrays coated with a high-reflective film. And we also present the optimized structural parameters and distribution pattern of the MOLGP. By the simulation of the professional optical software Lighttools, it's verified that the integrated MOLGP we proposed can achieve the functions of five complex-structure films in current typical backlight module (BLM), and the Five Parameters (light energy utilization efficiency, average illuminance and luminance, uniformity of illuminance and uniformity of luminance) in the BLM with integrated MOLGP are respectively 1.49, 1.40, 1.07, 0.91 and 0.97 times than those in the typical BLM. Obviously, the performance parameters of the MOLGP exceed the traditional design. Moreover, we design two sets of four-step masks of the ASCMCS by the graphical user interface (GUI). At last, we fabricate a 1.8 inch integrated MOLGP sample. Comparative experiments show that the Five Parameters of the fabricated MOLGP sample are respectively 1.43, 1.43, 0.97, 0.89 and 0.70 times than those of the typical BLM. The experimental results verify the feasibility of the concept of the integrated MOLGP proposed in this paper.

Light-guide plate using periodical and single-sized microstructures to create a uniform backlight system

Light-guide plates (LGPs) with aperiodic or size-varied microstructures are widely used in edge-lit light-source backlight systems for their high uniformity. In this Letter we designed a LGP with periodic and single-sized microstructures and analyzed the relationship between the holistic arrangement density of the microstructures and the uniformity. By controlling the holistic arrangement density of the microstructures, the uniformity could also be increased.

Polarized backlight with constrained angular divergence for enhancement of light extraction efficiency from wire grid polarizer

Efficiency of liquid crystal displays highly depends on the amount of polarized light emerging from the backlight module. In this paper, a backlight architecture using a nanoimprint wire grid polarizer for polarization recycling is proposed and studied, in which the extraction efficiency of polarized light is the major concern. The backlight module is composed of the stack of a wire grid polarizer, a lenticular array and a light guide plate. The light guide plate features interleaving v-groove and trapezoidal ridge coated with aluminum on the top surface, and scattering dot array on the bottom. The angular divergence of emerging light from the light guide plate can be well constrained so as to exploit the angular range with the best transmission of polarized light for the wire grid polarizer. The prototype of a 2.5-inch module has demonstrated an angular divergence of 48°. The overall extraction efficiency of polarized light enhanced by 21% and uniformity of 76% have been achieved.

Large-area and thin light guide plates fabricated using UV-based imprinting

As the demand of larger and thinner flat panel display increasing, conventional methods such as injection molding and hot embossing to fabricate light guide plates (LGPs) become difficult and unsuitable. This study reports a low-cost and high-throughput method to fabricate large-size (320 mm x 240 mm, 15" in diagonal) LGPs by using UV-based imprinting process. With the UV-based imprinting process, a large-size LGP with thickness down to 0.8 mm has been successfully fabricated. The optical property of fabricated LGP has been verified. This study has demonstrated the fabrication of large-size and thin LGPs by using UV-based imprinting process, and the possibility of UV-based imprinting process for fabricating other large thin optical elements.