Freeform Illumination Optics Research Articles

Freeform illumination optics design for extended LED sources through a localized surface control method.

Freeform illumination optics design with extended light sources to realize an accurate light control is very important, but still remains a challenging issue. Here, we propose a new method to design compact and efficient freeform lenses for extended sources. We employ a localized surface control strategy to directly modify the freeform surface to redistribute the light rays emitted from the extended LED source in a desired manner. By the combination of basic radiometry calculation and backward ray tracing, we obtain the irradiance distribution on the target plane and estimate the localized freeform surface to be modified. The optimization function with a Gaussian form is adopted to modify the localized surface. The smoothness of the freeform surface is taken into account in the optimization process to guarantee the processability of the freeform optics. We demonstrate the effectiveness of the proposed method with three design examples.

Synthesis of freeform optical surfaces using neural networks

Subject of study. Developed methods for synthesis of freeform illumination optics (ellipsoid, Monge-Ampere, string, and flow line methods) do not contain a correct description of the transformation of input and output wavefronts determined by the wave aberration function, do not consider the image quality criteria, and are not suitable for the calculation of imaging systems. The most common methods for synthesis of freeform elements of imaging systems (simultaneous multiple surface and ray-mapping methods) are also not ubiquitous because they are aimed at realization of a specific system configuration and, at least, require modification to solve a specific task. The largest complication in the synthesis stages of systems of imaging optics is the determination of the initial system scheme. Design of a method for synthesis of optical systems that does not require a starting point is a highly relevant objective of applied optics. A method allowing the synthesis of freeform optical surfaces for imaging systems using an artificial neural network is presented in this paper. Method. A neural network was built upon radial-basis functions and uses the geometric mapping method to generate the coordinates of the desired optical surface during backward ray tracing. The neural network was trained on different numbers of optical systems, which were automatically generated with variations in structural parameters and positions of the object and image. Main results. The method was demonstrated to operate effectively using more than 17,000 training systems at the ray set dimension of M=4096. The model of a flat-hyperbolic lens calculated using this method has a wave aberration of W<5×10−2 for wavelengths within the diffraction tolerance. Practical significance. The developed method can be used to design high-performance imaging systems.

Compact freeform illumination optics design by deblurring the response of extended sources.

Freeform illumination design for extended sources is a very challenging but rewarding issue that can benefit a wide range of illumination systems. Here, we propose a method that can achieve compact and highly efficient illumination lenses by deconvolving the blur caused by the extent from light sources. We combine the illumination calculation with the mathematical model of spatially variant convolution and develop a direct computational scheme to calculate the blur kernel without approximations. Two design examples with high optical performances are presented to demonstrate the effectiveness of the proposed method.

Freeform illumination optics for 3D targets through a virtual irradiance transport.

Freeform illumination optics design for 3D target surfaces is a challenging and rewarding issue. The current researches on freeform illumination optics are mostly involved in planar targets, especially for the cases where the targets are perpendicular to the optical axis. Here, we propose a general method to design freeform optics for illuminating 3D target surfaces for zero-étendue sources. In this method, we employ a virtual observation plane which is perpendicular to the optical axis and transfer the irradiance on the 3D target surface to this virtual plane. By designing freeform optics to generate the transferred irradiance distribution, the prescribed irradiance distribution on the 3D target can be realized automatically. The influence of the freeform optics size is considered in the optics design process, which makes it possible to design illumination system for near-field configuration where the influence of the freeform optics size cannot be ignored. We demonstrate the robustness and elegance of the proposed method with three design examples.

Design of freeform lenses for illuminating hard-to-reach areas through a light-guiding system.

Designing freeform optics for illuminating hard-to-reach areas is a challenging and rewarding issue. The current designs of freeform illumination optics are mostly valid in the applications in which the region of interest is easily accessible. What we present here is a general formulation of designing freeform lenses for illuminating hard-to-reach areas. In this method, the freeform lens consists of two elaborately designed surfaces, by which both the intensity distribution and wave-front of the light beam are manipulated in a desired manner. The light beam after refraction by the freeform lens is further guided through a light-guiding system to produce a prescribed illumination on a target plane which is inaccessible. The properties of the light-guiding system are taken into account in the tailoring of the freeform lens profiles to guarantee the prescribed illumination on the target plane. Two examples are presented to demonstrate the elegance of this method in designing freeform optics for illuminating hard-to-reach areas.

Least-squares ray mapping method for freeform illumination optics design.

Computing a source-target map that yields integrable surface normal field is quite challenging for freeform illumination design. Here, we propose a least-squares ray mapping method to calculate a superior ray mapping by iteratively correcting an integrable map to approach the energy conservation and boundary condition. The process is implemented via solving three minimization problems. The first two problems can be figured out pointwise and the third can be converted to two decoupled Poisson equations with Robin boundary conditions. We demonstrate the robustness and high efficiency of the proposed method with several design examples.

Precise light control in highly tilted geometry by freeform illumination optics

The control of light propagation in highly tilted geometry by freeform illumination optics has numerous applications. However, difficulties associated with the tailoring of freeform surfaces in tilted geometry significantly limit the scope of applications. Here, for the first time, to the best of our knowledge, we develop a general formulation for designing freeform illumination optics in highly tilted geometry. The numerical and experimental results show that when a precise control of light propagation is achieved, the freeform lenses are highly efficient and can significantly reduce glare and light trespass.

Design of Freeform Illumination Optics

AbstractFreeform optics constitutes a new technology that is currently driving substantial changes in illumination design. It liberates designers and engineers from restrictions of optical surface geometry, enabling them to achieve compact, lightweight, and efficient illumination systems with excellent optical performance. Freeform optics is currently used widely for both fundamental research and practical applications. This Review focuses on the design of freeform illumination optics, which is a key factor in advancing the development of illumination engineering. The design methods of freeform illumination optics can be divided into two groups: zero‐étendue algorithms based on ideal source assumption and design algorithms for extended light sources. The zero‐étendue algorithms include ray mapping method, Monge–Ampère equation method, and supporting quadric method. The algorithms for extended sources include illumination optimization, feedback design, and simultaneous multiple surfaces method. The characteristics and limitations of these design methods are illustrated and a summary of these methods with future outlooks is also given.

Design of a smooth freeform illumination system for a point light source based on polar-type optimal transport mapping.

A design method is proposed to generate smooth freeform illumination optics for a point light source based on the L2 optimal transport (LOT) mapping. In this method, the LOT mapping between an assumed circular planar source and a prescribed target is first obtained by solving a polar-type LOT problem. Then, the mapping calculated for the circular source is applied for a point light source. Finally, the freeform optical surface is generated by a geometric construction method to realize the ray mapping. As examples, a series of smooth-surface freeform lenses are designed for a point light source to form uniform and complex illumination patterns on rectangular targets. The ray-tracing results show that all the designs achieve excellent performance with the light utilization efficiency η over 0.87 (Fresnel loss considered) and the relative standard deviation (RSD) of the simulated illumination distribution less than 0.051 simultaneously.

Freeform illumination optics construction following an optimal transport map.

We present a modified optimal transport (OT) ray-mapping approach for designing freeform illumination optics. After mapping the source intensity into a virtual irradiance distribution under stereographic projection, we employ an advanced OT map computation method with the ability to tackle nonstandard boundary conditions. Following the computed map, we construct the freeform optical surface directly from normal vectors by requiring that the chord between two adjacent points is perpendicular to the average of the two normal vectors at these two points and enforcing this relationship with a least squares method. Examples of designing freeform lenses for LED sources show that we can produce various uniform illumination patterns with high optical efficiencies.

Tailoring freeform illumination optics in a double-pole coordinate system

We have developed a new method to design freeform illumination optics by introducing a double-pole coordinate system in ray mapping. This method establishes a much more accurate ray mapping by moving the two poles of the spherical coordinate system to the southernmost point of the sphere and overlapping them together. It can reduce surface error and improve illumination uniformity significantly. The residual surface error (RSE) of the freeform lens designed in the double-pole coordinate system is one magnitude smaller than that of the lens designed in the (θ,φ) coordinate system and is only 1/3 of that of the freeform surface designed in the (u,v) coordinate system.

Optimization of Free-Form Illumination Optics

We have developed optimization methods for generating free-form surfaces. The main applications are in the industrial on-line spectroscopic and machine visions measurements, where spectral and spatial uniformity, good efficiency and pass-line stability are required parameters. We used commercial software for ray-tracing engine. We have developed in-house optimization routines, but used also build-in functions. In this work we have designed a speckle free alternative for laser line generation based on the LED sources. The optical system is based on the collimation part and a free-form mirror. Simulation results are presented.