This PDF file contains the front matter associated with SPIE Proceedings Volume 11874, including the Title Page, Copyright information, and Table of Contents.

Previous work has shown it is possible to automatically optimize both directional pointing of light and its spatial distribution along light guide luminaires using prismatic light extraction elements. In addition to aiming light in the right direction(s), it is increasingly important that lamps are efficient. This is particularly true for electric vehicles, but it is generally important for reducing carbon emissions throughout automotive lighting. Since lamp test specifications are typically defined in terms of intensity test point requirements, it follows that an efficient design must approximate the overall distribution of the test point pattern. At the same time, a good lamp design should not sacrifice visual appearance for the sake of efficiency. As illustrated in previous work, when using prismatic extractors, one can point the centroid (average flux weighted direction of rays) in a desired direction(s). However, this does not always result in a high-efficiency system, nor does it guarantee alignment of the peak of the distribution with any specific direction (e.g. the test point pattern’s peak value). In some cases, it may also be desirable to change the appearance of the extractors themselves as viewed by an observer looking back at the lamp. In this work, we extend our optimization approach for light guide-based automotive lamps to include optimization of efficiency, particularly useful in electric vehicle applications. Specifically, we consider specialized aiming and tailoring of the lamp’s intensity distribution to better match the desired test point pattern; thereby increasing lamp efficiency. At the same time, we also consider visual appearance. To achieve better efficiency and visual appearance, we consider some different techniques to modify the light distributions. Some examples of ways to modify the distribution are: strategic use of fillets, prism face curvature, sharpness (Bezier) weighting factors, distributed prism aiming, and laser-etched surface texture solutions.

Advances in LED technology facilitate a variety of new application scenarios in automotive exterior lighting. Attractive features in this field are related to dynamic lighting scenarios. To replace mechanical adjustments of the past, the newest μLED technology provides a high-resolution source array based on a monolithic block of IC-chip, opto chip, and converter layer. Nevertheless, design and implementation of a corresponding optical system are required to project the μLED array onto the road.

Colored light for visual communication in cars at daylight conditions has recently started: A light guide with RGB LEDs is placed at the bottom of the windshield. Usage is safe visualization of autonomous mode and warnings beside e.g. wayfinding support, directional highlighting and turn signals. Today’s white luminance of light guides is about 1,250 cd/m² for daylight with a RGB luminance ratio of typically 28:65:7. A new proposal from an OEM requires the same luminance just for blue. Therefore we started an evaluation with different aspects as basis: The luminance of blue is low due to V(λ) curve but its color perception is high by Color Matching Functions, the lightness L* (perceived brightness) is related to luminance L by L* ~ L^0.44 and the RGB luminance ratio of traffic signs (acc. EN12966) is 35:50:15. We designed our car mock-up for a white luminance of 13,000 cd/m² using a RGB LED stripe reaching 1,500 cd/m² for blue. The surrounding simulates night to sunlight conditions with additional 100,000 cd/m² blinding sun. We tested 18 subjects (pandemic restrictions). The luminance of blue for “annoying” (= safe recognition) reached 900 cd/m² (sunlight + blinding). Additionally, the subjects had to adjust two neighboring colors to the same brightness or judge (brighter, same, and darker) for different colors. Our survey resulted in a reasonable luminance of 500 cd/m² for blue (emphasized by blinking) and a RGB luminance ratio of 35:50:15. The portion of blue is nearly doubled which forces a redesign of today’s automotive RGB LEDs.

Simulation of light propagation in a dispersed medium is usually based upon continuous medium approximation, which is good when the distance between different ray hits much exceeds the particle size. But when the different ray events are not statistically independent, which violates the continuous medium approach. Current paper investigates the problem for automotive paints where the particles are thin planar flakes. We performed accurate ray optics simulation. Here subsequent light scattering events are correlated: if incident ray reached the given flake, then the probability that the reflected ray leaves the paint area without further scattering is higher than the probability of hitting a flake “on average”. If, however, the reflected ray hits the next flake while going upwards, then it will be reflected downwards and most likely hit the first flake again. After that the probability of hitting the same second flake is increased as compared to mean value. This increases the probability of uneven scattering while decreases that of even scattering. We demonstrate how this affects the total scattering and obtain some analytic estimates. We compare the bidirectional reflection function of paint surface calculated for the two models and show how the difference changes with concentration and flake size. It happens that a serious change is in the near-specular region. Some analytically derived “correction” terms can be applied to the continuous medium approach to move it towards the results of the explicit model. In some cases this improvement can be a due compromise with more expensive explicit one.

Currently, the vehicle-to-vehicle communication systems is actively developing, where various wireless communication technologies are used. One such technology is wireless optical communication. However, most research has focused on designing and testing electrical circuits using standard optical elements such as spherical lenses. In this paper, we propose an effective method for designing hybrid free-form optical systems, which would provide a given spatial distribution of the signal-carrying light radiation within a given angular field.

Monte Carlo ray tracing has been shown to be both a robust and reliable method for optical modeling of illumination systems. The typical approach traces rays through an optical system and averages the rays in spatial and angular bins to provide estimates of the illuminance and intensity. While Monte Carlo methods are commonly used with incoherent sources, they can also be used with coherent sources. The primary difference between the two simulation types is the inclusion of the phase difference between binned rays in the illuminance and intensity calculations. The phase information can be stored in a ray’s optical path length, which is updated as a ray is traced through a system and when a ray encounters specific interfaces, such as the π phase shift due to a reflection from a surface of higher index. Thus, when careful consideration is given to the phase changes that occur during a ray trace, it is possible to use Monte Carlo methods to model illumination systems that require coherent sources, such as interferometers. Furthermore, with the ability to model coherent sources, beamlet based approaches are also effective. Comparisons are presented. In general, a common challenge for Monte Carlo simulations is the large number of needed rays to overcome statistical noise. However, it is possible to reduce the number of traced rays using various methods, such as: source aiming, scatter aiming, and Backwards Ray Trace. These methods minimize the number of traced rays by using knowledge of the system to selectively avoid tracing rays which will not contribute meaningful data to the output distribution. Monte Carlo ray tracing can also be computationally expensive. To prevent rerunning a costly simulation, it is advantageous to save the traced rays and post process the data for further analysis and studies. For example, the rays can be defocused to a plane at a different distance, re-binned for a difference receiver resolution, or filters can be used to remove rays based on specific criteria like whether they passed through a specific surface. This paper is organized with three main sections. First, we discuss Monte Carlo ray tracing to model interference. The second discusses Monte Carlo ray tracing for modeling diffraction using a Huygens-Fresnel approach. The last summarizes the paper.

LEDs not only have widely varying spectral (and electrical) properties at the fixed temperature and current "grouping conditions" used to characterize them after production, to group them into "bins". LED spectrum and voltage also change with temperature and current in operation. For an actual product, it is nontrivial to predict spectra and voltages from limited information in data sheets for real life driving conditions. We show how spectra and voltages can indeed be predicted from data sheet values, and which generic a priori information about LEDs is required in addition, demonstrating our open source, public domain Matlab implementation.

In the field of endoscope optics we see more and more zoom designs, realized by tuneable lenses, micro actuators or traditional lens movement in rigid endoscopes with a camera sensor. For such devices, a lighting concept that adapts the beam angle to the current field of view of the zoom optics is desirable. In endoscopes, the light is usually transported from a source to the tip by a light guide or fiber bundle.1 Since it is not feasible to place an optical system at the fiber exit to fulfill the task, one would make use of the fact that a fiber roughly conserves the angular distribution of incident light and transfer the task of variable beam generation to the light source. We present an optical system that performs this task by conventional optical means outside the endoscope. A LED is imaged to the fiber entrance by a system of variable focal length. By choosing the source etendue equal to that of the fiber, it is ensured that the proper magnification of the imaging is accompanied by the specified angular extent. The LED light is first collimated, and the exit pupil of the collimator is imaged by a system of moving and fix lenses. In a final step, we show a design to adapt a colored light source to the variable beam optics.

Laser cutters and engraving devices traditionally feature a high-power CO₂ laser in combination with a scanning unit. However, within the laser processing industry, a growing interest arose in the use and combination of laser diode sources, enabling a more compact design featuring a longer estimated lifespan. Therefore, we investigate and compare different laser diode combination configurations, while evaluating their applicability in a compact laser scanning configuration. Specifically, as a case study, we target the combination of 4 high-power laser diodes, pursuing a collimated, homogenous and symmetrical output beam, while minimizing light losses. An optimal laser diode combination design was achieved by use of aspherical lenses, knife-edge mirrors and a polarizing beam splitter. Two laser diodes are oriented to emit p-polarized light, while the other emit s-polarized light. In front of each laser diode, an aspherical lens is mounted to collect and collimate the laser beam. The two collimated s-polarized laser beams and the two p-polarized beams are each combined using a knife-edge mirror, after which the s- and p-polarized beam are combined by a polarizing beam splitter, giving rise to a single collimated output beam that can be used as input for the scanning unit. Following the optimization and tolerancing of the design, the laser diode combination system was successfully demonstrated in a proof-of-principle laboratory configuration indicating a homogeneous and collimated illumination beam at the entrance of the scan head, paving the way towards the integration and combination of multiple laser diode sources for use in high-power laser cutting and marking applications.

The traditional bi-directional stochastic ray tracing with photon maps (BDPM) is a popular method for physically accurate lighting simulation. Although it has been improved by application of MIS there are still problems such as the optimal number of rays. The implementation of the BDPM runs progressively, iteration by iteration, tracing a number of light and camera paths and then merging them. The noise achieved after a fixed rum time does not always decrease with the number of rays, so there is some optimum. We produce the method of calculating the optimal number of rays. Variance of the contribution to luminance calculated by BDPM in one iteration depends on the number of rays via a relatively simple algebraic law, yet more sophisticated then for classic Monte Carlo because the merged paths are not statistically independent in BDPM. The noise after the given simulation time is determined by this variance divided by the number of iteration done within that time, so the law includes the average time spent on tracing one light and one camera ray. Expectedly for the optimal number of camera paths the resulting noise is homogeneous over the image. One can make relative or absolute noise to be homogeneous so we have a single value for the whole image. The resulting formula includes “time per camera/light ray” only as a weighted sum over all pixels which can be easily measured from a single trial tracing. With this optimal choice the noise is reduced considerably.

The emergence of OEM and industry benchmarks [1-6] raised the expectation regarding automotive headlamps performance in the last decade, resulting in growing benefits regarding traffic safety. Concomitantly, designing headlamps has grown in complexity, especially for low beam and high beam applications. Fulfilling all requirements concurrently is challenging, not merely due to the large number of requirements to keep track off during development, but predominantly due to the simultaneous inclusion of lamp- (luminous intensity) and vehicle-based (illuminance) metrics in the design. In this paper we propose and demonstrate an alternative design methodology for the development of forward lighting systems with the goal of reducing development time, providing superior photometry, and providing more structure to the development process. Instead of iteratively adjusting optical surfaces and running subsequent simulations to validate each design step, checking whether the change could achieve the respective design objective, we are subdividing the overall design problem into multiple steps and solve multiple inverse problems instead. Specifically, we compile all requirements into a unified set of luminous intensity requirements. Subsequently, we create analytical light distributions that meet this total set of requirements. Once validated, the resulting target light distribution is fragmented into multiple light distributions, which are then used as individual design targets for the creation of freeform surfaces in support of each optical sub-component. The total light distribution is obtained by superposition of all partial light distributions.

Fingerprinting-based Visible Light Positioning is a promising candidate to perform large-scale indoor positioning tasks. In fingerprinting, signal characteristics are grouped in a fingerprint map together with the respective locations inside the indoor environment. By comparing live signal measurements with the fingerprint map, the closest match is selected as the current position estimate. However, the fingerprint map has to be generated beforehand in the so-called offline phase, which is the time-consuming process of sampling the environment, in which the positioning task is desired, for signal characteristics. Here, we propose a fingerprint-based positioning approach for which we mitigate the need for the offline phase by taking advantage of the VLC data transmission capabilities of the LED luminaires of the obligatory room lighting. Based on the transmitted data on room and luminaire configurations to the receiving device, the illumination characteristics in the room can be calculated by simplified analytical formalisms, substituting the need for an experimentally measured offline phase. We demonstrate the effectiveness of our approach with the help of ray-tracing simulations and under the assumption that the receiving device is equipped with an angular sectored receiver. The results of the ray-tracing simulations mimic real world measurements with the receiver in the online phase. We show that decimeter level accuracies down to centimeter level accuracies are achievable for such an approach.

Rigid endoscopes are optical systems characterized by high light losses and poor light transfer efficiencies below 20 %. We investigated this issue first by performing a photometric analysis of three state of the art endoscopes and second by carrying out an optical analysis by means of an optomechanical model with the optical design software LightTools (Synopsys). The light losses in the material and the critical interfaces of the optomechanical model are then analyzed by considering both the spectral power distribution of the light source and the light distribution that is coupled into the endoscope’s illumination optics. To improve the illumination optics of rigid endoscopes three approaches are presented in this work: a compound parabolic concentrator and a fiber cone are first developed as alternative coupling elements but only a minor improvement could be realized, because the present optical system is highly constraint by étendue law. Therefore, an immersion element is secondly introduced between coupling element and fiberbundle to reduce backscattering between the interfaces and to increase the overall light transfer efficiency. However, it turned out that a 10 % increased light transfer efficiency can be achieved only by selecting high numerical aperture fibers combined with the immersion element. Third, the influence of the initial coupling element’s geometry on the light distribution in the surgical field is investigated. The optical simulations show that by lengthening the coupling element’s truncated cone the light can be distributed more uniformly in the surgical field.

As a new non-destructive imaging technology in the field of biomedicine, photoacoustic imaging technology combines the advantages of pure optical and pure acoustic imaging with good spatial resolution, high sensitivity, and strong penetrating power. In the photoacoustic microscopy imaging system, the acousto-optic coupling prism is a component for optical transmission and ultrasonic detection. It is usually composed of an irregular prism and a spherical concave acoustic lens at the bottom. Because the spherical acoustic lens has a poor focusing effect on the ultrasonic beam, the accuracy of ultrasonic detection is low. In order to solve this problem, we propose an optimization method to eliminate the influence of acoustic lens on the beam transmission. A collimating lens is added to the acousto-optic coupling prism with an aspheric acoustic lens at the bottom of the system. In this paper, Zemax optimizes the curvature coefficient and thickness of the collimating lens to eliminate the deteriorating effect of the aspheric acoustic lens on the beam transmission, and evaluates the optimization effect by analyzing the spot and MTF image. The simulation results show that the collimating lens can eliminate the influence of the aspheric acoustic lens on the beam transmission, so that the optical focus and the acoustic focus can be kept coaxial and confocal, and the detection efficiency of the photoacoustic signal can be improved. This work has theoretical guiding significance for the study of photoacoustic microscopy imaging with large depth of field.

As a kind of carcinoma with extremely high mortality and morbidity, there are immense demand for early detection and diagnosis of gastric carcinoma. At present, in medical research, the initial detection of gastric tumors mainly uses the laser detection methods. The Monte Carlo method has good adaptability for exploring the process of photon transportation, therefore, it has the value of extension and application in the research of photons’ transportation in biological tissues. Through exploring the influence of the tumor in gastric tissue on the photon transmission, it can help determine the existence of gastric tumor. After established the corresponding model, we using the program to perform the fitting process, analysising the result then we can draw a conclusion that: according to the trajectory analysis of photons, gastric tumors absorb more photons than the gastric tissues, and such basic features can be used to determine the existence of gastric tumors. Through the analysis of optical absorption density and fluence rate: when photons initially enter the first gastric tissue layer(the Z-axis 0-0.2cm region), because the water layer’s weak optical absorption and scattering effects, optical absorption decreases slowly: from 0.0805cm-1 drop to 0.073cm-1. After entering the second layer, the layer of gastric tissue, because the absorption and scattering effect of gastric tissue is higher than water, the optical absorption density rises sharply to 8.7028cm-1, then with the photon weight vdecreasing, the optical absorption density continues to drop to 0.7128cm-1. After entering the third layer, the layer of gastric tumor, the optical absorption density rises again. When z=0.5cm, the optical absorption density approaches to 1.8848cm-1 and then slowly drops to 0.1338cm-1. Finally, photons enter the second layer of gastric tissue and water layers, and continue to decrease to approach 0cm-1. These data demonstrate that there are effects of gastric tumor on photon transport in gastric tissues. This research will also provide reference and theoretical guidance for the optical imaging and diagnosis of gastric tumors.

The theoretical, design, technological and software aspects of creating a dynamically controlled LED surgical lamp for contrast visualization of biological tissues during surgical operations are considered. The concept of design a surgical lamp, which combines white light illumination and dynamic control colored illumination, is proposed. It allowed both to reach high-quality illumination of the operational field and to improve the contrast of visualization of different biological tissues and objects. An optical system of the lamp, which allows achieving maximum and uniform illumination and provides uniform color mixing all over the operating field, is considered. Surgical lamp used both phosphor-conversion white LEDs for general illumination and monochrome AlInGaN, AlGaInP LEDs for precision control of color illumination. The developed software allows you to independently change the intensity of six spectral LED components: blue (460 nm), cian (505 nm), green (530 nm), lime (550 nm), orange (590 nm) and red (630 nm) to synthesize colored lighting in wide chromaticity scale. Also, within a wide range, it is possible to change the luminance and color temperature of the general illumination from white phosphor LEDs. Color and luminance evels are controlled by pulse-width modulation of the LED current. The light parameters of the surgical lamp are set by remote computer connected to the lamp via Bluetooth. To determine optimum illumination conditions for contrast visualization, optical characteristics of different biological tissues in combination with color LED emission are investigated. As a result, the experiments on animals showed the contrast of biological tissues imaging increases when they were illuminated with specially selected spectra emitted by developed lamp.

Photoacoustic imaging (PAI) is an emerging and efficient imaging technology based on the discovery of the photoacoustic effect. It is a medical imaging technology used for internal imaging of human tissues. It combines the advantages of acoustic imaging and optical imaging. However, because it achieves high resolution through the intense focus of the laser beam, the resulting photoacoustic image will have a poor depth of field and less structural information. In order to solve this problem, an end-to-end general network fusion framework based on convolutional neural networks is applied to extract important image information from the input image through the convolutional layer, and then we use appropriate fusion rules for feature fusion, and finally the fusion features are processed to obtain large-volume and high-resolution photoacoustic images. Analyzing the source image and the fusion image can prove that the model embodies good generalization ability and excellent experimental results in the process of photoacoustic image fusion.

Most of the freeform lens optimization methods for LED beam shaping are focused on producing rectangular illumination patterns. Here we demonstrate the generation of non-rectangular irradiance distributions by optimizing the 'uv'-polynomial freeform surface, where (u,v) are stereographic coordinates. An initial freeform surface is designed with an optimal transport ray mapping method that is suitable for unconventional boundaries. Simulated annealing is then used to optimize the polynomial coefficients based on an automated workflow that links Matlab (central platform and optimization engine), Rhinoceros (3D molding) and LightTools (Ray tracing).

Tolerance analysis is an integral part of the design process that saves time and money while improving the product quality. Nevertheless, tolerancing of illumination optics is often glossed over by the current industry. Consequently, there is a need to understand and establish tolerancing in illumination optics. This research focuses on single surface deformation. In the process referred to as surface perturbation, the surface is perturbed by a known amount. Then, the changes on the irradiance target are evaluated. A localized surface perturbation, like a bump or hole, results in either a local increase in irradiance with an annulus dip around the elevated irradiance or a local decrease in irradiance with an annulus increase around the decreased irradiance. Such an outcome is a result of flux conservation. The ratio between the height and the surface area (referred to as the size) of the localized surface perturbation has an approximately linear relationship to the largest irradiance change. Once the linearity of the relationship is understood for the localized surface perturbation of a particular size, the tolerance range can be estimated for other localized surface perturbations sizes. Within the optics’ tolerancing range, the Laplacian of the surface perturbation predicts the irradiance change. As long as the ray-mapping between the surface and the target is known, the Laplacian of the surface change can be mapped onto the target. The surface change also perturbs the ray-mapping. Thus, taking the perturbed ray-mapping into account enables prediction with greater accuracy. Using this method, expected surface deformation from the manufacturing process can guide estimating irradiance changes, providing a first-order method to tolerance illumination optics.

Freeform optics are used to create complex application-adapted illuminance distributions due to their high number of adjustable degrees of freedom. As with conventional optics, this can result for some applications in large optics that exceed the available installation space or lead to high production costs. While the use of Fresnel lenses is common in such cases for conventional optics, the Fresnelization step in the design process of freeform optics is more complex due to the lack of rotational symmetry and only done for specific cases. Therefore, this paper presents a method to examine different segmentation strategies on freeform lenses and to optimize Fresnelization parameters. In this work, the method will be demonstrated using a head-up display (HUD) as example, in which the combination of a Fresnel lens and a display creates a moiré pattern in the illuminance distribution. In order to accelerate the simulation of complex Fresnel freeform optics considerably, a special ray tracing algorithm is developed, which takes advantage of the segmentation characteristics. The simulation approach of the illuminance distribution and the optimization of the Fresnelization are shown and discussed on a lens with about 300 segments visibly reducing the moiré pattern.

The methods of wave optics and ray-field tracing are implemented for modeling microlens arrays (MLAs), taking into account the effects of coherence and polarization of the light source, randomization of the parameters of microlens arrays. The influence of the parameters of the radiation source (wavelength, curvature of the wavefront, beam radius, coherence radius, etc.) and the microlens array (periodic or random, aspect ratio, pitch size, refractive index, shape and profile of the array surface (convex, concave, aspheric), etc.) on the output parameters (intensity distribution, radiation pattern, optical efficiency) of the diffracted beam is studied. The numerical simulation of the intensity distribution and the spreading angle of diffracted beam is carried out. To calculate the optical efficiency of microlens arrays, a new approach to the ray field based on the coherent state representation has been developed. Such wave rays can simply be tracked along arbitrary curved surfaces. A user-friendly interface has been developed for entering the initial parameters of the light source and the MLA array, as well as for displaying graphical and informational modeling results. The measured intensity distributions of diffracted radiation by microlens array are compared with the simulation results for LD and LED sources.