Zhenrong Zheng

Freeform LED lens for uniform illumination

Light flux from LED must be redistributed to meet the needs of lighting in most cases, a new method is proposed for its secondary optic design. Based on refractive equation and energy conservation, a set of first-order partial differential equations which represent the characters of LED source and desired illumination were presented. The freeform lens was constructed by solving these equations numerically. The numerical results showed that we can get a freeform lens for the illumination of uniformity near to 90%, with considerable high computation speed. This method can shorten the designing time of the freeform lens with high accepted tolerance.

Freeform illumination design: a nonlinear boundary problem for the elliptic Monge–Ampére equation

We propose an approach to deal with the problem of freeform surface illumination design without assuming any symmetry based on the concept that this problem is similar to the problem of optimal mass transport. With this approach, the freeform design is converted into a nonlinear boundary problem for the elliptic Monge-Ampére equation. The theory and numerical method are given for solving this boundary problem. Experimental results show the feasibility of this approach in tackling this freeform design problem.

A 360-degree floating 3D display based on light field regeneration

Using light field reconstruction technique, we can display a floating 3D scene in the air, which is 360-degree surrounding viewable with correct occlusion effect. A high-frame-rate color projector and flat light field scanning screen are used in the system to create the light field of real 3D scene in the air above the spinning screen. The principle and display performance of this approach are investigated in this paper. The image synthesis method for all the surrounding viewpoints is analyzed, and the 3D spatial resolution and angular resolution of the common display zone are employed to evaluate display performance. The prototype is achieved and the real 3D color animation image has been presented vividly. The experimental results verified the representability of this method.

Design and fabrication of an off-axis see-through head-mounted display with an x–y polynomial surface

An off-axis optical system with an x-y polynomial surface for a see-through head-mounted display (HMD) is presented. With the use of an x-y polynomial surface, an off-axis see-through HMD system with one tilted spherical combiner and six relay optical lenses is designed. An off-axis see-through HMD with a 15 mm exit pupil, a 40 degrees x 30 degrees FOV, and 70 mm eye relief is achieved. Furthermore, a binocular off-axis see-through HMD prototype is fabricated and the performance of the system is experimentally tested; 972 cd/m(2) of luminance is measured at the position of the exit pupil of the HMD. A typical augmented reality image captured outdoors with the HMD prototype is also demonstrated.

A mathematical model of the single freeform surface design for collimated beam shaping

Incoherent collimated beam has a wide application, and reshaping the collimated beam with freeform optics has become a popular and challenging topic of noniamging design. In this paper, we address this issue, embedded in three-dimensional space without any symmetry, with a freeform surface from a new perspective. A mathematical model is established for achieving the one-freeform surface design based on the problem of optimal mass transport. A numerical technique for solving this design model is disclosed for the first time, and boundary conditions for balancing light are presented. Besides, some key issues in achieving complex illuminations are addressed, and the influence of caustic surface on this design model is also discussed. Design examples are given to verify these theories. The results show elegance of the design model in tackling complex illumination tasks. The conclusions obtained in this paper can be generalized to achieve LED illumination and tackle multiple freeform surfaces illumination design.

Optimization design of irradiance array for LED uniform rectangular illumination.

Light-emitting diode (LED) large-scale uniform rectangular illumination has a wide range of applications and is usually created by an irradiance superposition scheme. Abandoning the traditional method, we propose an approach to generate this illumination mode and enhance efficiency. With this method, an independent rectangular irradiance distribution is generated by each LED lens unit, and the large-scale illumination is obtained by arraying the irradiance distribution. Two slim direct-lit LED backlightings with a distance-height ratio of 3 were designed. An optical performance with irradiance nonuniformity less than 0.0228 and efficiency greater than 96% were obtained. Compared with the traditional methods, the efficiency is significantly enhanced and the number of the LED units is dramatically reduced by this new method.

Freeform lens arrays for off-axis illumination in an optical lithography system

We propose a method of designing a freeform lens array for off-axis illumination (OAI) in optical lithography to produce desired OAI patterns and improve efficiency. Based on the Snell law and the conservation law of energy, a set of first-order partial differential equations are derived and the coordinate relations for each OAI pattern are established. The contours of the freeform lens unit are calculated numerically by solving the partial differential equations, and the freeform lens array is obtained by arraying the lens units. Moreover, the optical performance for each OAI pattern is simulated and analyzed by software. Simulation results show that the irradiance distribution of each OAI pattern can be well controlled with a maximum uniformity of 92.45% and a maximum efficiency of 99.35%. Also, analysis indicates that this method has the advantages of reducing the complexity of the exposure system and having good tolerance to the input intensity variations of the laser beam.

Optimized design of LED freeform lens for uniform circular illumination

An optimization method is proposed for designing an LED freeform lens which produces a uniform circular pattern with high energy efficiency. This method is composed of three main aspects: design of the initial guess, parameterization of the freeform surface, and construction of the merit function. The initial guess is created by solving an ordinary differential equation numerically. An approach of selecting optimization points is introduced for parameterization of the freeform surface. The merit function is constructed by use of the irradiance uniformity and the efficiency of the lens. Design examples are given, and the results show that the irradiance distribution is well controlled with a maximum uniformity (the relative standard deviation of irradiance, RSD) of 0.0122 and a maximum efficiency of 93.88%. This optimization method can be generalized to design freeform lenses with different lighting patterns or without rotational symmetry.

Conceptual design of dedicated road lighting for city park and housing estate.

We propose dedicated road lighting, which is significantly superior to the existing lighting technologies for the city park and housing estate. This dedicated lighting employs freeform surfaces to effectively control the optical field of the LED source to produce three kinds of illumination modes for the curved road, straight road, and the small public square, respectively, perfectly matching the road conditions of the city park and housing estate. A mathematical model of freeform illumination design is presented to achieve a conceptual design of this road lighting, and a numerical technology for solving this design problem is introduced for the first time, to our knowledge. An illumination model of this conceptual design is constructed. The experimental results of the conceptual design tally closely with the target. This dedicated road lighting, integrated with energy saving, healthy lighting and artistic beauty, provides a beautiful landscape for the city park and the housing estate at night, and will play an important role in improving quality of life of the urban inhabitants.

Virtual display design using waveguide hologram in conical mounting configuration

An improved virtual display is proposed by using a waveguide holographic configuration with two total internal reflection holographic gratings in conical mounting and two volume hologram in classical mounting recorded on a single transparent planar waveguide. Using this compact configuration, efficiency can be dramatically improved and assembly is easy to be realized. The main principle and the method of intensity uniformity control are present in the paper. The analysis and simulation results are also explained. The virtual display system design shows good optical performance with 25 deg. field of view, a large pupil about 43 mm, little distortion less than 1%, and low aberration. The configuration can be used to a portable or wearable display.