This PDF file contains the front matter associated with SPIE Proceedings Volume 13022, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Freeform optics for illumination, pioneered over 20 years ago, are now widely used to light up streets, automobiles, architecture and more. But many questions remain: Do we have good, accessible design methods, especially for extended sources? Do we have proven processes to estimate and specify tolerances, to ensure full production yield without overengineering? Do we fully understand diffractive structures on freeform surfaces? The talk discusses the progress of design and manufacturing methods over the last 30 years, shows the knowledge gaps we’re suffering from, and concludes with an outlook to a non-obvious but exciting new approach for coherent light: What happens when we combine freeform surfaces with scattering and spatial light modulation?

Using an optical fiber to guide light towards a sample plane is a highly efficient and compact solution. However, because of the angular intensity distribution of the light exiting the fiber, directly aiming the fiber at a surface would create a very non-uniform irradiance profile, which is undesired in many applications. Several optical techniques exist to homogenize the light beam, but most of them require a significant amount of space. Here, we investigate different methods to transform a Gaussian intensity profile into a round flat-top irradiance profile, while limiting the total system size to dimensions similar to the required output beam (24 mm). The intensity profile used is based on goniometric measurement, while Ansys Zemax OpticStudio is employed as raytracing software to optimize the various optical configurations. Firstly, ray-mapping techniques are used to map the input intensity to the desired output irradiance, in combination with the optimization of refractive and reflective optical elements. Secondly, solid light pipes are investigated to mix the input rays and project them onto the sample plane. Lastly, small and inexpensive hollow volume scatterers are studied to diffuse the light effectively and homogenize it. In this way, the root-mean-square irradiance (uniformity) could be reduced from 0.90 to 0.08 W/cm², with losses less than 20%.

Previous work has demonstrated the optimization of spatial distribution, angular pointing, angular widths, and design efficiency of light guide luminaires using prismatic light extraction elements. See, for instance, [1]-[4]. Increasingly, in the automotive industry—and for signal lighting in particular—light guide luminaires that use secondary arrays of micro-optics are becoming more common. Typically, these secondary micro-optics are used either to scatter light selectively (micro partially scattering arrays), or to steer light (for example, micro prism arrays). In this work, we focus on the latter type of secondary optic arrays: micro prism arrays. As in previous studies, for this work, all geometrical elements were created in, and optical simulations were performed in, a CATIA V5 Based environment [5]. We build on previous optimization techniques to create signal lamps; used in conjunction with arrays of prismatic elements that are part of secondary lenses. The secondary lenses are used to refine the angular distributions further. These modifications help to meet intensity test point specifications while at the same time preserving quality visual appearance. Typical sizes of the arrays studied are 0.25mm to 1mm pitch, with tens of elements to tens of thousands of elements.

We present an example of design, tolerancing and fabrication of freeform plastic lightguides for optical sensing applications. The design of the lightguides relies on Nonimaging Optics principles and uses raytracing simulations for analysis and optimization. We examine the influence of fabrication parameters on the simulated performance and show ways to minimize their impact. The presented lightguides have been fabricated at the Photonics Innovation Center of VUB – B-PHOT.

Uniform illumination, including uniform irradiance and color uniformity, is of indispensable importance for numerous imaging and sensing applications. These illumination designs typically comprise one or multiple light-emitting diodes (LEDs), or feature halogen sources, which are preferred for spectroscopy applications. We present an overview of different design strategies enabling a uniform illumination, taking the extended source characteristics into account, while aiming to compare different optical design approaches with respect to cost, efficiency, complexity, scalability and robustness. Four case-studies will be compared: (1) considering geometrical optimization of the source positions, (2) combination of a halogen source array with a biconic aspheric lens array, (3) combination of a multi-chip LED with a biconic lens array and Fresnel lens, and (4) the combination of a multi-chip LED with a Shell-Mixer. A design-for-manufacturing approach is applied for all designs, considering integration and robustness, paving the way towards industrial uniform illumination optics.

The Gemini North Adaptive Optics (GNAO) facility is the upcoming AO facility for Gemini North providing a state-of-the-art AO system for surveys and time domain science in the era of JWST and Rubin operations. The adaptive optics bench receives both natural star and laser guidestar light from the telescope focus and relays it, via a path that includes a high-rate deformable mirror and a tip-tilt mirror, to science instruments, at 2x magnification. The relay splits off light in a bandwidth of 350 nm - 800 nm for use in three wavefront sensors: a tip/tilt sensor and a low order wavefront sensor using natural guidestar light, and a 4-channel laser guidestar wavefront sensor, supporting a narrow field and a wide field mode (12 arc seconds and 2 arc minutes respectively). The optical design requirements on the relay are demanding. In particular, exceptionally tight control of distortion was required for the science field, which precluded conventional relays using pairs of off-axis paraboloids. A novel optical system has been produced that meets all of the GNAO AOB requirements. This design is based on an asymmetric version of the Offner relay. A particularly novel aspect of this relay is that there is no collimated light path within the system, and in this paper it is shown that the system meets all performance requirements without needing such a space. Unlike the normal Offner relay, the “Modified Offner Concentric” (MOC) relay produces an accessible pupil, clear of the confusion of rays at the M2, allowing placement of a flat deformable mirror there. The MOC design is presented here and is shown to be competitive in this application to conventional AO relays, providing superior performance with reduced complexity.

There are several aspects of optimizing multi projection system illumination. A main driver in the illumination performance are the light sources, their spectral characteristics, brightness and etendue. The impact of these characteristics on the architecture of illumination design and their implications for key performance metrics such as luminous flux and projectable color space is addressed. The transformative role of solid-state light sources, which have advanced the development of illuminations with high luminous flux and wide color spaces is stressed. The emergence of new challenges posed by the latest generation of coherent light sources is highlighted and advanced illumination design strategies to overcome them are presented.

A light tube is an alternative representation of etendue in the phase space. They were first investigated by Zimmer, examples of various fields of optics were presented in. The search for a perfect illumination for a given optical system can be understood as a task to fill a light tube or its phase space with light. The way for illumination design starts with an identification of the relevant properties of the optical system which can be characterized via the light tube concept. The etendue of a light tube is calculated via Hottel’s formula or its approximations for important special cases. Knowing the etendue allows for source selection. We show various design approaches – imaging and non-imaging - to adress this task.

Retinal imaging has always played a major role in the detection and management of ocular disease and a wide range of retinal imaging techniques exist. Most of them, however, focus only on high image quality (field, 2D or 3D resolution) but neglect spectral information. The aim of this study was to develop a versatile lighting module in order to easily perform multispectral imaging with a conventional fundus camera. Taking advantage of the development of multi-color LEDs, we have built a source with 8 LEDs allowing to take images in white light and at 7 wavelengths ranging from 395 to 730nm. The LEDs fit on a surface of 33mm2 and are electronically controlled via an Arduino module. The design of the source allows it to be easily positioned in a conventional camera to replace the lighting bulb. The illumination module was tested in a TOPCON-TRC-NW6S fundus camera using a model eye. The proximity of the LEDs makes it possible to obtain a good optical image without additional modification of the system. This low-cost device makes it possible to easily modify a wide range of classic camera into a multispectral camera in order to more easily explore the potential of this technique.

Freeform surfaces are optical surfaces without linear or rotational symmetry. Their flexible surface geometry offers high degrees of freedom, which can be employed to avoid restrictions on surface geometry and create compact yet efficient designs with better performance. Therefore, freeform surfaces can endow beam shaping with more new functions and satisfy the ever-growing demand for advanced beam-shaping systems. The Monge-Ampère (MA) equation method converts the design of freeform beam-shaping optics into an elliptic MA equation with a nonlinear boundary condition. The MA method can automatically satisfy the integrability condition and be implemented efficiently. In this talk, we will introduce the principles behind the MA method and reveal the mathematical essence of illumination design based on ideal source assumptions. Also, several interesting beam-shaping systems will be provided to show the effectiveness of the MA method in a wide variety of applications.

We introduce the development process of a new headlight module with perfect colour mixing and sharp upper edge for use as an additional module. Light is nearly collimated (<0.5° cone angle) for a variety of high-power automotive LEDs illuminating up to 1000 m street in front of the car. Key to success is an optimization process not only of the optical elements but also the materials and parameters of the injection molding process. A feedback loop of geometry measurement and simulation of real geometries does lead to acceptable tolerance values and geometry deviations. Finally, the optics in the module needs to be optimized with respect to mechanical tolerances and the inevitable fabrication errors. In this case it resulted in an additional element to be added at the entrance and exit surface of the initially designed optical structure. All steps were accompanied or carried out by simulations with LucidShape and FRED.

Solar energy, when accidently focused, can cause wildfires and melt plastics. Solar irradiance concentration analysis can help to optimize wanted concentration or avoid unwanted concentration. This article provides a workflow on how to perform solar irradiance concentration analysis using light simulation software. As an example, an automotive headlight will be used. One analysis approach is to filter the object surface sensors for the maximum irradiance value of a given sun position. All maximum irradiance values can then be mapped in relation to the horizontal and vertical sun position, creating a solar irradiance map. If the maximum irradiance value of this map is below a given threshold, then the analyzed product is safe for sun exposure.

For a long time, imaging optics in automotive lighting played only in the field of -comparably simple - singlet projection lenses for headlamps. In this time, a key focus of automotive illumination optics design was on controlled free-form shapes. With the rise of matrix-headlights, new imaging tasks and specifications came up in automotive optics design. Most recent developments like high resolution micro-LEDs for digital headlighting and near field projection of signaling functions, as well as the use of Micro-Lens-Arrays boost the imaging optics methods in automotive lighting. [1-6] Digital functionality, design aesthetics, energy (optical) efficiency, complementary to mass manufacturability and cost effectiveness are defining the boundary conditions for automotive lighting system design. This paper tries to elaborate an overview of recent imaging tasks in automotive illumination optics design and their related specifications and limitations. Designing the full systems, dense interfunctionality with the light source itself and non-imaging elements plays a key role in meeting design targets. Photometric analysis combines input from light source characteristics, intensity targets and system size. As results, efficiency limitations and imaging system specifications are direct results. These optical design approaches will be demonstrated based on several different application examples: Adaptive Driving Beam matrix headlights as well as projection signals show the specific interaction of imaging subsystems with illumination optics.

We previously proposed an iterative wavefront tailoring (IWT) method [Optics Letters 44(9): 2274-2277] to solve the freeform lens design problem for irradiance tailoring, where the entrance surface can be predefined as a spherical, aspherical or freeform surface. Here, this method is adapted to address a more challenging design problem where the exit surface is predefined. We design a freeform lens with a fixed aspherical exit surface to demonstrate the effectiveness of the modified method.

Uniformity is a critical performance issue in illumination design. When Etendue is considered, the two main options to achieve uniformity are mixing rods and lens arrays. Mixing rods are quite effective, but they often require a large package size. We have explored a Turn-Mixer concept based on a turn prism with TIR surfaces and embedded partial mirrors. This approach provides uniformity in a small package size. And, by using two Turn-Mixers, both spatial and angular mixing can be achieved.

We present several geometrical models for freeform optical design based on Hamilton’s characteristic functions, which can be either expressed in terms of a cost function or a generating function. The models are closed with an energy balance. We give an example of an inverse design for a near-field optical system.

To design an ultra-small blue micro light emitting diode μ-LED (< 5 μm) with high light extraction efficiency is one of the bottlenecks currently. How the extraction efficiency can be boost of a very small sized μLED is taking the attention of most of the researchers. As the surface-to-volume ratio of μLEDs is much larger than traditional LEDs. We designed and developed a miniaturized GaN-based vertical blue μLED and conduct a systematic research by simulating the structure in finite-difference-time-domain (FDTD). We develop a miniaturized state of the art blue μ-LED (GaN) which exhibits high light extraction efficiency of 70.4% having the size of 1 μm × 1 μm. The μ-LED is backed by multi distributed Bragg reflector to achieve the high extraction efficiency, M-DBR consists layers of Ti₃O₅ and SiO₂. During investigating the proposed μLED design we derived that the light extraction efficiency (LEE) has a strong dependency on some of the structural parameters of μ-LED i.e. thickness of each layers specifically MQW, μ-LED chip size, chip shape, orientation and position of the dipole source. The proposed GaN-based blue μ-LED structure is evaluated, simulated and optimized for different dipole orientation and positions with different chip sizes and shapes. At end come up with the smallest and most optimized vertical blue μ-LED structure for future display applications.