Zhenfeng Zhuang

Flat-Concave Dual-Mirror Configuration Design for Upright Projection-Type Ultrashort Throw Ratio Projectors

An off-axis flat-concave dual-mirror (FCDM) configuration for an ultrashort focal length projection lens based on the digital light processor (DLP) upright projection-type projector is proposed in this paper. This projection lens is composed of two lens groups: the FCDM system and the relay optical system. The flat mirror and the contour of the concave mirror are determined according to the relationship between the chief ray from the exit pupil of each field of view (FOV) and the corresponding assigned position on the screen. A curved image is formed between exit pupil and concave mirror, aiming to correct field curvature. The second lens group consists of a set of conventional refractive lenses which convert a curved object onto the image panel. Based on this method, a projection lens with an ultrashort throw ratio (TR) of 0.34, including a full FOV 139.8 ° and distortion of less than 1%, is designed. Additionally, the colorimetric performance, uniformity, optical efficiency and size of the designed projector are analyzed. Results show that the proposed projector system with high optical performance is compact and suitable for household or educational applications.

Multi-element direct design using a freeform surface for a compact illumination system

An iterative optimization algorithm is introduced to address the surface iterative errors as well as source extension issues in a freeform illumination system for producing satisfactory illumination distribution. A unique two-parameter coordinate system is utilized to represent the emitted ray directions. Then, the direction vector for the incident rays, which propagate through several surfaces, is obtained using ray-tracing techniques. Based on the mapping between the incoming rays and a target grid, a freeform surface is generated as a good starting design. An iterative optimization strategy is further employed to alleviate the deterioration of illumination distribution on the target region, and the uniformity of the illumination system is evaluated during optimization. Very few variables are demanded, and more flexibility in the design of the freeform surface is offered. Successive iterations can be performed until the desired result is attained. An optical system is used as an example to demonstrate the validity of the proposed method, and numerical simulations are carried out to evaluate the optical performance. The simulation results show that a small angular intensity distribution and prescribed rectangular illumination pattern can be achieved simultaneously.

A freeform optics design with limited data for extended LED light sources

Abstract This paper proposes an optimization method for designing a freeform lens which can produce a good uniform circular illumination distribution and obtain high efficiency on the target plane. The initial surface profile of the freeform lens is calculated based on the laws of reflection and the energy conservation law, and then is fitted using the non-uniform rational basis spline (NURBS) method. The control points and weights are applied to parameterize the shape of freeform lens. The merit function for the optimization is defined as relative standard deviation (RSD) of the simulated illumination from the desired illumination and the efficiency of the lens. The simulation results indicate that the RSD is shown to be lower than 0.157, and maximum efficiency can be as high as 83.9%. In addition, it is demonstrated that this algorithm can obtain high uniform illumination distribution on the target plane with less variables. Compared with the conventional method, the simulation results show that the modified algorithm converges with less variables, good uniformity and high efficiency. Moreover, a freeform lens with different lighting patterns and non-rotational symmetry can be produced by the proposed method.

Directional view method for a time-sequential autostereoscopic display with full resolution

A time-sequential autostereoscopic three-dimensional (3D) display using a set of cylindrical optical elements (COEs) as the backlight steering is proposed. The operation principle of the system and its detailed design are described. In our system, the COEs control the direction of the backlight for the proposed system of the users right and left views. Additionally, the displayed images can be observed under ambient lighting by implementing the high density light-emitting diode (LED) arrays. Compared to the first-generation array display, the image resolution is greatly improved by the addition of the time multiplexing technique. A prototype system using a set of COEs, LED arrays, two linear Fresnel lenses, and an elliptical diffuser is constructed. Here, the directional backlight beams are synchronized with the right and left images alternately displayed on the liquid crystal display (LCD) screen, and two convergent viewing zones are formed alternately in front of the users eyes; then 3D images are perceived because of persistence of the vision of human eye. The experimental results show that the proposed method is a potential technology for 3D applications such as 3D television.

General construction method for a rotationally symmetric ultrashort distance catadioptric projector.

In this work, the off-axis imaging of a fan of rays with a rotationally symmetric mirror is studied, based on which a general construction method is proposed for the design of a rotationally symmetric ultrashort distance catadioptric projector. With the proposed method, the intermediate images at arbitrary planes of incidence can be obtained, and thus the designer has the freedom to choose suitable intermediate images to simplify the aberration correction of the catadioptric starting point. To prove the effectiveness of the proposed method, the construction process of a convex-type ultrashort distance catadioptric projector is presented. The intermediate image at the meridional plane is discontinuous, and the image distances for some fields are infinite. In contrast, the intermediate image at the sagittal plane is continuous, smooth, and finite-and thus is selected to correct the skew aberrations in the catadioptric starting point. An initial configuration, which has small aberrations, is obtained without increasing the system complexity. Further automatic optimization is applied to the initial configuration to get the optimal solution. The simulated performance of the optimal solution is excellent.

Large-aperture transparent beam steering screen based on LCMPA

A large aperture transmissive step-steering screen composed of a liquid crystal microprism array (LCMPA) deflector and a 90° twisted nematic liquid crystal (TN LC) polarization modulator is developed. The designed 3 in. (7.62 cm) device provides a steering angle of 0.95° that differs from the projected value by only 1.26% and the angular difference caused by dispersion is less than 5%. Using two-layer cascaded screens a three-direction beam steering system for stereoscopic displays is achieved with a steering step of 0.95°, undesired residual polarization contrast less than 2%, and high optical uniformity.

Two-layer optimized light field display using depth initialization

In this paper, we propose a method to optimize two-layer light field display using depth initialization. In contrast to existing trade-off work between performance and processing time, this paper firstly models the display principle of layered light field display, and then performs layered initialization with the prior known depth of 3D objects, and finally optimizes the layered images for light field display. Experiments demonstrate that the proposed initialization method can obviously save the iterations and related processing time for the existing online or offline algorithms to achieve the same reconstructed peak signal to noise ratio (PSNR) and present a better subjective reconstructed performance using the same computation resource.

Addressable spatial light modulators for eye-tracking autostereoscopic three-dimensional display using a scanning laser

A scanning laser-based back light three-dimensional (3D) display capable of rendering full-resolution, low crosstalk, and vivid 3D depth perception has been developed by incorporating time-sequential multiplexing and eye-tracking technologies. This system includes three main subsystems: a scanning laser module, a relay transfer unit created by combining multiple transmissive-type electrically addressed ferroelectric liquid crystal spatial light modulators (FLC-SLMs), and a dual-directional transmission screen (DDTS) unit that can produce different angular magnification factors in both the tangential and sagittal planes. The light beam is directed by the DDTS after transmission through FLC-SLMs, and left and right eye viewing zones are produced sequentially in accordance with the locations of clear apertures in the FLC-SLM that are controlled based on data from the eye-tracking system. Owing to the persistence of human vision, 3D images are formed as a result of the high-speed scanning backlight and fast response characteristics of the FLC-SLM. A prototype of the proposed 3D display was designed and built, and experiments were carried out. The experimental results verify the feasibility of the proposed scheme, and full-resolution images with natural 3D perception are demonstrated by the prototype.

Numerical investigation of three-dimensional pupil model impact on the relative illumination in panomorph lenses

Abstract. One of the key issues in conventional wide-angle lenses is the well-known cosine-fourth power law problem causing the illumination falloff at its image space. This paper explores methods of improving illumination in the image space in panomorph lenses. By tracing skew rays within the defined field of view and pupil diameter, we obtained the actual position of the three-dimensional pupil model of the entrance pupil (EP) and exit pupil (XP). Based on the law of irradiance transport conservation, the relation between the area of the EP projection and illumination in the image space is derived to investigate the factors affecting the illumination on the peripheral field. A panomorph lens has been optimized as an example by providing a self-defined operation in the optimization process. The characteristic of the EP and XP in panomorph lenses is qualitatively analyzed. Compared with the conventional design method, the proposed design strategy can enhance the illumination with and without polarized light based on qualitatively evaluating the area of projected EP. It is demonstrated that this method enables the enhancement of the illumination without additional film coating.

Subpixel area-based evaluation for crosstalk suppression in quasi-three-dimensional displays

A subpixel area-based evaluation method for an improved slanted lenticular film that minimizes the crosstalk in a quasi-three-dimensional (Q3D) display is proposed in this paper. To identify an optimal slant angle of the film, a subpixel area-based measurement is derived to evaluate the crosstalk among viewing regions of the intended subpixel and adjacent unintended subpixel by taking the real subpixel shape and black matrix into consideration. The subpixel mapping, which corresponds to the optimal slant angle of the film, can then be determined. Meanwhile, the viewing zone characteristics are analyzed to balance the light intensity in both right and left eye channels. A compact and portable Q3D system has been built and appropriate experiments have been applied. The results indicate that significant improvements in both crosstalk and resolution can be obtained with the proposed technique.