Electric‐field‐driven LC lens for 3‐D/2‐D autostereoscopic display

Abstract— The use of an electric‐field‐driven liquid‐crystal (ELC) lens cell for switching between a 3‐D and 2‐D display is proposed. Due to the phase retardation of the non‐uniform LC directors, an ELC lens functions the same as a geometric lens. The parameters of an ELC for 3‐D applications are optimized through the simulation of the electrode configuration and voltage levels. A prototype was made where the ELC lens is placed in front of a liquid‐crystal display (LCD) 15 in. on the diagonal with a 99‐μm subpixel pitch. Under zero voltage, the ELC lens is a transparent medium and the users can see a clear 2‐D image. In 3‐D mode, the ELC lens array performs the same as a cylindrical lens array to the incident vertical polarization under suitable driving voltages. Placing a half‐wave plate between the LCD and ELC lens is proposed to change the polarization of the LCD to be parallel with the polarization lens direction of the ELC lens. The measurement of the horizontal luminance profile, performance of the ELC lens, and feasibility for 3‐D/2‐D switching was verified. The fabrication process for the ELC lens is compatible with the current LCD production process and enables the accurate control of the lens pitch of the ELC lens.     

Resolution enhancement of integral‐imaging three‐dimensional display using directional elemental image projection

Abstract— A new approach to resolution enhancement of an integral‐imaging (II) three‐dimensional display using multi‐directional elemental images is proposed. The proposed method uses a special lens made up of nine pieces of a single Fresnel lens which are collected from different parts of the same lens. This composite lens is placed in front of the lens array such that it generates nine sets of directional elemental images to the lens array. These elemental images are overlapped on the lens array and produce nine point light sources per each elemental lens at different positions in the focal plane of the lens array. Nine sets of elemental images are projected by a high‐speed digital micromirror device and are tilted by a two‐dimensional scanning mirror system, maintaining the time‐multiplexing sequence for nine pieces of the composite lens. In this method, the concentration of the point light sources in the focal plane of the lens array is nine‐times higher, i.e., the distance between two adjacent point light sources is three times smaller than that for a conventional II display; hence, the resolution of three‐dimensional image is enhanced.     

Crosstalk‐free dual‐view integral imaging display

We propose a crosstalk‐free dual‐view integral imaging display. It is composed of a display panel, a barrier array, and a micro‐lens array. The central barrier is located at the vertical central axes of the display panel and the micro‐lens array to split the element image array and the viewing zone. Moreover, other barriers are located at the margins of the elemental images and corresponding micro‐lenses to eliminate the crosstalk. The lights emitting from the left and right half of the element image array are modulated by the left and right half of the micro‐lens array to reconstruct the right and left viewing zones, respectively. A prototype of the proposed dual‐view integral imaging display is developed, and good experimental results agree well with the theory.     

Fabrication of pinhole/micro‐lens array for improving resolution of integral imaging 3‐D display

In this paper, we present a new fabrication of micro‐lens array (MLA) with pinhole array—pinhole/micro‐lens array (P/MLA) for integral imaging 3‐D display (II), which combine lithography and ink‐jet printing. A black circular groove array (BCGA) is used as pinhole array, and laser 3‐D microscope and a homemade setup have been used for the characterization of P/MLA. The results show that high‐precision P/MLA can be obtained using BCGA as templates. By controlling the driving voltage at different steps, the distance between nozzle and substrate, as well as the number of liquid droplets, P/MLA with smooth morphology, different sizes, good repeatability of geometry parameters, great uniformity of focusing, and good converging performance can be achieved. For demonstration, P/MLA with curvature, focal length, numerical aperture, and F‐number of 815.8 μm, 1.60 mm, 0.1311, and 3.8 are applied for the reconstruction in II, exhibiting good reconstruction performance with high resolution, and BCGA reduces the influence of stray light on II and improves the quality of the reconstructed image.     

A wide‐scanning ellipsoid lens antenna fed by phased array antenna

Luneburg lens antennas have been widely applied to many communication systems for their multibeam scanning and high gain characteristics. However, the large profiles of conventional Luneburg lens antennas restrict their applications. To solve these issues, an ellipsoid lens antenna fed by phased array antenna (PAA) operating at Ka‐band is proposed in this article. The profile of the ellipsoid lens is reduced by half compared to the conventional Luneburg lens, based on the transformation optics theory. The wide‐angle scanning property is obtained by optimizing the amplitude and phase distributions of the PAA, combined with the element pattern superposition principle. The proposed five‐layer ellipsoid lens antenna is able to scan up to ±45° with less than 3 dB scanning loss at 28 GHz. Finally, the lens was easily fabricated through three dimensional printing technology and computer numerical control. Experimental results are in good agreement with the numerical results, thus validating the proposed design.     

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.     

A compact wideband dual‐polarized linear array with hybrid structure and resistive loadings

A wideband, wide‐scan dual‐polarized linear tightly coupled dipole array is presented. The array is based on a prior work, but it employs a hybrid design of planar cross‐finger dipoles and vertical tapered dipoles to form a non‐oversampled aperture with reduced array width and robust structure. Moreover, wider bandwidth and lower profile height are also achieved in the array as compared to the prior work by introducing resistive loadings between dipoles and ground plane, at the expense of acceptable gain loss. Consequently, the array with width of 99.8 mm and profile height of 86.3 mm provides a performance of 5.7:1 bandwidth (0.35‐2 GHz) for active Voltage Standing Wave Ratio (VSWR) < 3.0 while scanning up to 50°, with orthogonal port isolation below ?15 dB. A 1 × 18 prototype array was fabricated and measured, showing good agreement with simulations.     

Design of multi‐beam antenna based on Rotman lens

A planar Rotman lens antenna that generates multiple beams is presented over a wide angular range. The proposed multi‐beam antenna consists of a Rotman lens and a ten‐element printed Yagi antenna array. By properly comparing optical aberrations, expressing as the normalized path length errors Δl, the suitable ratio of on‐axis to off‐axis focal length (g = G/F) is acquired so as to minimize phase errors for the array elements. Ten dummy ports are employed to reduce the performance deterioration caused by energy reflection. A prototype with seven input ports was fabricated and measured, covering a wide scanning angle of 60° (–30°, 30°). The measured beam patterns show that the seven beam gains are distributed from 11.9 to 13.6 dBi under operating of 8.15 GHz. Both the simulated and measured results are used to verify the design approach.     

Short focal length tunable liquid crystal lenticular lens array based on fringe field effect

A liquid crystal (LC) lenticular lens array based on fringe field effect is proposed. The gradient refractive index (GRIN) profile can be generated in the LC layer because of the fringe field between the strip‐shaped electrodes and the bottom electrode. The proposed LC lenticular lens array possesses ideal lens‐like phase profile and shortest focal length (1.199 mm) when the driving voltage is 5.4 V. The focal length can be tuned with millisecond response time by changing the driving voltage of the proposed LC lenticular lens array. The rise time τ_rise and decay time τ_decay of the proposed LC lenticular lens array are 162 and 94 ms, respectively.     

A planar triple band four element antenna system with polarization and pattern diversity for LTE/WLAN/DSRC applications

This paper presents a low profile, triple band antenna system for LTE/WLAN/DSRC applications. It consists of four coplanar waveguide (CPW) fed printed inverted F antennas (PIFAs), each loaded with folded slot antenna (FSA) and folded resonator (FR). The loading of FSA and FR is responsible for the triple band property. An independent/semi‐independent control of each band is observed. Each radiating element is aligned perpendicularly to its adjacent element to employ polarization and pattern diversity. This helps in sustaining a good isolation level in between them without using any additional decoupling networks. The antenna has been fabricated and measured to validate the simulated results. Measurement reveals three 10 dB return loss bandwidths in the ranges 2.47‐2.62 GHz, 3.39‐3.64 GHz, and 5.74‐6.25 GHz, respectively. The isolation levels between the radiators are more than 20 dB at all three operating bands. Respective peak gains are 3.8 dB, 4.5 dB, and 5.3 dB. To gratify the requirement of the diversity performance, some essential attributes like Total Active Reflection Coefficient (TARC), Envelope Correlation Coefficient (ECC), Diversity Gain (DG), Mean Effective Gain (MEG), and Channel Capacity Loss (CCL) are also evaluated.     

基于双焦点设计的平面波束扫描透镜天线研究

为了提升平面透镜天线的扫描性能,以实现波束扫描或多波束应用,首先研究设计了单焦点平面透镜天线,针对单焦点平面透镜天线在大角度扫描时增益降低太快的问题,引入了反射阵和传统介质透镜的双焦点设计方法。基于阵列天线合成理论,计算了双焦点透镜天线的辐射特性。采用多层金属孔阵列单元,建模了平面透镜天线模型,仿真对比了单焦点透镜和双焦点透镜天线的扫描辐射特性。结果表明,在扫描范围（0°-27°）内,双焦点透镜天线的最低增益相对于单焦点透镜天线有明显提升,而且大角度扫描方向图形状也有改善,证明了双焦点的设计方法有效提升了平面透镜的扫描性能。     

LC GRIN lens mode with wide viewing angle for rotatable 2D/3D tablet

To widen the vertical and horizontal angular ranges where the lens performs well, the off‐axis performance of a liquid crystal gradient index (LC GRIN) lens is analyzed by the combined simulation system of an LC director simulator and a ray‐tracing simulator. We found that the angular difference between an LC alignment direction and an electrode array direction of the LC GRIN lens is one of significant parameters, and detailed conditions of structure are established. The measurement result shows that the developed structure reduces the degradation ratio in a luminance profile from 61% to 3.2%. We have applied a user tracking system for the rotatable 3D display, equipped with a detection of a panel orientation and a face position. As a result, we have developed a rotatable 2D/3D tablet whose 3D viewing azimuth angle is over 30° in both landscape and portrait orientations.     

Design of an integrated optical pickup with NA of 0.85 for small form factor optical disk drives

We design an integrated optical pickup for small form factor optical disk drives. The specifications of the pickup are compatible with those of the Blu-ray disk (BD) in terms of numerical aperture (NA) of the objective lens, the wavelength of the laser diode, and the thickness of the cover layer. The objective lens unit with NA of 0.85 consists of two aspherical refractive lenses and a diffractive optical element for compensation of the chromatic aberration. Each element of objective lens unit will be fabricated on a wafer as an array type, and the three wafers will be aligned and bonded to form an objective lens array. Therefore, elements of the objective lens unit are designed to have sufficient alignment tolerances for various directions such as de-center and tilt. The optical performances of the objective lens unit are evaluated by simulation against various disturbances such as wavelength change of emitting light from laser diode, misalignments, etc. We also design a quarter wave plate, a polarized holographic optical element, and the shape of photodiode integrated circuit array to generate focusing and tracking error signals. The entire height of the pickup including working distance is 2 mm, and the effective pupil diameter of the objective lens unit is less than 1 mm.     

A novel design of high performance multilayered cylindrical dielectric lens antenna using 3D printing technology

In this work, design and realization of high performance, low‐cost X‐band multilayered cylindrical dielectric lens antenna (MLCDLA) is presented using 3D printing technology. Firstly, MLCDLA is designed and simulated in the complete 3D CST microwave studio (MWS) within the X‐ band as consisting of six layers and being fed through a conventional rectangular waveguide (WR90). These layers are in the form of cylindrical discs having different radii, thicknesses and made of a cheap polylactic acid material. These layers have also varying dielectric constant from 1.2 to 2.7 that are compatible for fused deposition modeling (FDM) based 3D‐printing process. Secondly, a prototype of MLCDLA is produced by using a FDM based 3D‐printer. 3D printed dielectric lens antenna is measured and a good return loss of almost more than 10 dB within the X‐band with a high gain of 16‐18 dBi are achieved as compared with the counterpart alternative designs. Thus, it can be concluded that the proposed novel design and prototyping method not only achieves the high radiation performance characteristics along X‐band but also is a fast, low‐cost, and effective method for prototyping dielectric lens structures for the microwave applications.     

Both transversal negative permeability and backward‐wave propagation in X‐Band waveguide with double‐side SRR metamaterials

In this article X‐band rectangular waveguides partially filled with the double‐side single ring resonator (DSRR) array are investigated for miniaturization, stop‐band, and multi‐band filters applications. Several rectangular waveguides loaded with the DSRR array in 2–10 GHz frequency band have been studied and optimized. We observe both the transversal negative permeability presented above the cutoff frequency and the backward‐wave located below the cutoff frequency with the DSRR array in X‐band waveguide. Both simulation and measurement results of DSRR array are with good agreement. The DSRR array provides better performance of the transversal negative permeability and the backward‐wave than the split‐ring resonator array. The physical explanation of backward‐wave is presented. The power loss distributions are clearly presented for the negative permeability attenuation and the backward‐wave propagation. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:240–246, 2016.     

The implementation and performance evaluation of a silicon-based LED packaging module with lens configuration

This study develops a transfer molding with flexible master for a silicon-based light emitting diode packaging with an aspherical lens and a microlens array using microelectromechanical systems technology. By transferring the pattern from wafer to wafer, the precise alignment of the lens configuration and the reflector of the silicon substrate can be achieved; batch processing can be used to reduce the costs. The size of the packaging element can be further reduced to allow more applications. For evaluating the packaging performance, the transfer of the pattern of various lens profiles is accomplished successfully using silicone gel and electroplating nickel as the lens molds, and experiments to determine the mechanical reliability are conducted. The experimental results show that the lens profiles of the silicone gel and nickel masters are exactly transferred onto the surfaces of epoxy and silicone gel encapsulations, respectively, without any damage to the material surface. The brightness of the packaging elements with a single aspherical lens profile and high fill factor microlens array are increased by 26 and 16 %, respectively, as compared with optical encapsulation with a smooth curved surface. The light uniformity is greatly improved for a 100 % fill factor microlens array. The proposed packaging solution satisfies the requirements of pattern transfer in a wafer level and improves lighting performance.     

A lightweight multi‐beam cylindrical Luneberg lens antenna loaded with multiple dielectric posts

A multi‐beam cylindrical Luneberg lens antenna loaded with multiple light dielectric posts for the purpose of light weight is presented. The antenna is based on a parallel‐plate waveguide and specifically composed of 10 E‐shaped patch antennas feeds, 2 parallel plates, and 491 epoxy posts. The equivalent gradient index of the Luneberg lens antenna is realized via the positions of the epoxy posts between the parallel plates. The features of low‐profile height (0.55λ) and large radiating area (4.4 × 0.55λ²) of the cylindrical Luneberg lens result in wide beamwidth in elevation plane and high gain while operating at 4 GHz. Consequently, the 3 dB beamwidth in the elevation plane is >65°. Furthermore, the multi‐beams cover a wide scan angle of 120° in the azimuth plane. The measured aperture efficiency of the fabricated lens antenna is above 50% from 3.9 to 4.3 GHz. In addition to the good radiation performance, features of light weight and ease of fabrication have also been demonstrated for the proposed lens antenna.     

An improved method of designing optimum microstrip Rotman lens based on 2D‐FDTD

In this article we propose an efficient method for analysis of microstrip Rotman lens using two‐dimensional finite difference time domain (2D‐FDTD). Both the dielectric and conductor losses are modeled in this method in order to achieve results which are in good agreement with 3D simulation. Using 2D analysis, the required simulation time is reduced considerably, which in turn, enables us to use the proposed analysis method in an optimization procedure. Based on this optimization procedure, we present an improved design of a microstrip Rotman lens in which both the efficiency and also the gain of isotropic antenna array are increased. In this design, the Rotman lens has 5 beam ports and 16 array ports and operates in Ku frequency band.     

Perspective correct occlusion‐capable augmented reality displays using cloaking optics constraints

Perspective‐correct occlusion‐capable augmented reality displays are generalized using an optical cloak constraint for ray transfer analysis or simulations; any ray entering the optical system exits at the height and angle as if it passed through empty space. We analyze several systems with two‐lens, three‐lens, and four‐lens looped groups in inline, folded, and looped configurations. We design and demonstrate a four‐lens folded optical cloak and a three‐lens inverted cloak with an erecting prism.     

Beam‐pattern synthesis using slotted Rotman lenses

In this article, the design principle of the Rotman lens is reviewed, and an X‐band lens for 10‐GHz operating frequency is simulated and analyzed. Rotman lenses with circular and elliptical slots of different orientations are simulated, and their associated radiation patterns are plotted too. The characteristics of the radiation patterns generated by a linear array antenna and the slotted Rotman lenses are functions of the shape, dimensions, location, and orientation of the slots etched on the metallic surface of the lenses that feed the array. The computer simulation results demonstrate that, in addition to the other significant advantages of microwave lenses, there is a strong potential for using slotted Rotman lenses as convenient microwave devices for beam‐pattern synthesis. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.