Integrated micro-optical light guide plate

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.

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.

Multifunctional graphene metasurface to generate and steer vortex waves

Graphene, an innovated 2D material with atomic thickness, is a very promising candidate and has drawn great attentions in various applications. Graphene metasurface enables dynamic control of various wavefronts, achieving distinguished functionalities. The flexibility of graphene metasurface makes it possible to implement multifunctional devices with ease. In this work, a novel design of multifunctional graphene metasurface, which can combine the functionalities of generating and steering vortex waves, has been proposed. The multifunctional graphene metasurface consists of a large array of graphene reflective unit cells. Each unit cell is controlled independently by its size and external static gate voltage. By scrutinizing the reflective property of the graphene cell, the graphene metasurface is designed to realize multi-functionalities. Simulation results show that vortex wave can be generated and steered. This work can establish a methodology to design multifunctional graphene metasurfaces, and the tunability of graphene opens the gate to the design and fabrication of reconfigurable graphene devices.

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.

Terahertz Wideband Filter Based on Sub-Wavelength Binary Simple Periodic Structure

In this paper, a silicon-based terahertz wideband filter was designed using rigorous couple wave theory to achieve high diffraction efficiency and wideband filtering performance. The optimal parameters, such as filter period, duty ratio, and groove depth, are given. The design value and tolerance analysis were carried out to obtain the allowable deviation range of each structural parameter of the filter. The device was fabricated and tested for performance. The experimental results were consistent with the design results, proving the feasibility of the design method and can be applied in terahertz, communication, imaging, and other fields.

High-efficiency directional backlight design for an automotive display

We propose a high-efficiency directional backlight module (DBM) for automotive display applications. The DBM is composed of light sources, a light guide plate (LGP), and an optically patterned plate (OPP). The LGP has a collimator on the input surface that serves to control the angle of the light emitted to be in the horizontal direction. The OPP has an inverse prism to adjust the light emission angle in the vertical direction. The DBM has a simple structure and high optical efficiency. Compared with conventional backlight systems, the DBM has higher optical efficiency and a suitable viewing angle. This is an improvement in normalized on-axis luminous intensity of 2.6 times and a twofold improvement in optical efficiency. The viewing angles are 100° in the horizontal direction and 35° in the vertical direction. The angle of the half-luminous intensity is 72° in the horizontal direction and 20° in the vertical direction. The uniformity of the illuminance reaches 82%. The DBM is suitable for use in the center information displays of automobiles.

Research on Design of Tri-color Shift Device

An azimuth-tuned tri-color shift device based on an embedded subwavelength one-dimensional rectangular structure with single period is proposed. High reflection efficiencies for both TE and TM polarizations can be achieved simultaneously. Under an oblique incidence of 60°, the reflection efficiencies can reach up to 85, 86, and 100 % in blue (azimuth of 24°), green (azimuth of 63°), and red (azimuth of 90°) waveband, respectively. Furthermore, the laws of influence of device period, groove depth, coating thickness, and incident angle on reflection characteristics are investigated and exposed, and feasibility of the device is demonstrated. The proposed device realizes tri-color shift for natural light using a simple structure. It exhibits high efficiency as well as good security. Such a device can be fabricated by the existing embossing and coating technique. All these break through the limit of bi-color shift anti-counterfeiting technology and have great applications in the field of optically variable image security.

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.

Fast optimization method based on the diffuser dot density for uniformity of the backlight module

A fast optimization method based on the diffuser dot density (DDD) for uniformity of the backlight module (BLM) is proposed in the paper. First, the relationship between the efficiency of the light emerging and the DDD is analyzed, and then a simulation model that is employed to acquire a serial of simulating data is constructed. Second, a mathematic method to profit the relationship is adopted, and a polynomial relationship is derived. Finally, an algorithm to adjust the DDD and optimize the uniformity of the BLM based on the DDD is constructed. The simulation results prove that only by three times optimization, the uniformity of the BLM can reach 85.6%, and the experimental result indicates that the algorithm proposed in the paper can improve the uniformity rapidly. The final experimental result is that the uniformity of the third optimization reaches 77.4%, which satisfies the target 75% in the phase of designing the BLM. Compared to the conventional optimization method, the method can speed up the procedure and lower the expense of developing the BLM in fabricating the liquid-crystal display.

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.

Planar optical correlators integrated with binary optical lens

Planar optical correlators (POCs) can achieve smaller volume of optical system and hence have important applications to identify dynamic targets in complex scenarios. POCs, however, generally have serious astigmatism and optical efficiency loss introduced by its refractive lens with a zigzag optical beam. To conquer the disadvantages of POCs, we propose a type of binary optical planar-integrated optical correlator. The correlator incorporates two pieces of reflective binary optical lens as Fourier transform lens and one spatial light modulator as a programmable filter. The off-axis aberrations commonly occurred in POCs can be corrected by using reflective binary optical lens instead of refractive lens. As a model of hybrid numerical-optical correlator using optoelectronic interface, the proposal is helpful to improve the integration and flexibility and robustness of POCs.

Research of micro-prism distribution on the bottom surface of the small-size integrated light guide plate

The luminance uniformity of the backlight module (BLM) importantly depends on the microstructure distribution on the bottom surface of the light guide plate (LGP). Based on the small-size integrated LGP (ILGP) proposed, we put forward a distribution expression of micro-prisms on the bottom surface of the ILGP, and present the relational expressions between the coefficients of the analytical expression and the structural parameters of the ILGP, such as the light guide length L, width of the ILGP W, thickness of the ILGP H, and space between light emitting diodes (LEDs) d. Then, the research results above are applied to the design of the small-size ILGPs. Not only can the micro-structure distributions on the bottom surface of the ILGPs be directly given, but also the simulation results show that the luminance uniformities of the integrated BLMs are higher than 85%. The research indicates that the expressions proposed in this paper are correct and effective, and have important guiding significances and referential value.

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%.