This PDF file contains the front matter associated with SPIE Proceedings Volume 7103, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Response surface modeling (RSM) is described as a tool to perform optimizations and sensitivity analysis in optical modeling. With this method, the behavior of the system is first mapped out using a limited set of ray-tracing simulations, carefully spanning the full parameter space. This can already be done before the full merit function is known. The relation between design parameters and system performance is then approximated by fitting the simulation results to functional forms. All subsequent optimizations are then performed very time-efficiently on the functional descriptions of the dependencies. This contrasts with direct optimization, where the computationally intensive optical modeling is in the loop of the optimization algorithm, and where changes in merit function, mapping out trade-offs, and determining sensitivities, are very time consuming. The paper will discuss the advantages of RSM with respect to direct optimization and give recommendations for the type of problems that are preferentially addressed by RSM. The method will be illustrated by a case: how optical simulations were used in the design of Lumiramic^TM phosphor conversion components for LEDs.

Illumination systems suffer from tolerances like all optical systems, including gross, process, roughness, and system errors. A common system error in solid-state lighting (SSL) luminaires is source variation due to variation within selected LED bins. Tolerances of LED bins include peak or dominant wavelength and flux output. These bin variations lead to chromatic shifts in the resulting illumination distribution when discrete spectral emitters are mixed to provide a desired color. Software tools are developed to provide ease in inspection of color mixing of discrete spectral LEDs taking into account the selected bins for each LED. This tool is a graphical user interface (GUI) of standard LED products from a series of LED manufacturers. Using this tool the color mixing of red, green, and blue LEDs are presented, showing that there is a color shifts in the resulting distribution due to binning variation. Optics that have the potential to alleviate the color shifts due to LED bin tolerances are presented.

High-Power-LEDs have reached a development stage that affords their reasonable application to general illumination. Nonimaging total internal reflection optics (TIR optics) that generate non-rotationally symmetric light distributions are proper components to preserve the advantages associated with this type of light source. Thus, high efficiency has to be reconciled, e.g., with the use of freeform surfaces. This contribution investigates the development of TIR optics for LED-based illumination applications. First, we consider rotationally symmetric TIR optics in order to illustrate their functional principle and demonstrate some special design criteria. Second, we apply them to non-rotationally cases using the tailoring technique. Finally, we illustrate various aspects of the design process with selected examples.

We propose an easy-to-handle method of surface parameterization which is valuable for enhancing the illumination design process. Therefore, an additional normal vector function is provided defining the desired direction of the virtual normal vector at each point of the surface. Hence, the reflection/refraction properties are seperated from the shape of the surface. These surfaces are named Virtually Reflecting/Refracting Surfaces (VRS). This type of surface provides the opportunity to alter the normal direction without changing the shape of the surface and vice versa. Therefore, the designer can have a selective look at those quantities depending mainly on position or on direction. This means that, e.g., one can first prescribe the geometrical shape and adjust the surface's optical properties afterwards. Moreover, structured surfaces, e.g., segmented reflectors, can be replaced in between by virtually reflecting surfaces in order to eliminate discontinuities. This is apparently expedient for improving the convergence in automatic design. We investigate optical layouts with VRS to demonstrate their impact on the design and the optimization process.

We developed a hollow light guide (HLG) model which allows to predict the best extractor combination for any given HLG length and for typical constraints like mean illuminance values and uniformity. The HLG prototype we analysed has a diameter of 30 cm, a 16 m length, 3M prismatic structures on the inner walls, curved light-reflecting surfaces with different shapes working as light extractors. It is powered by a projector with a 400W HIT-lamp. Firstly, we characterised extractors by their flux "consumption" and extraction. Then, we developed an analysis software to allow real time acquisition of floor illuminance data by means of a cooled, calibrated photometric CCD camera. We thus modeled the HLG as a lineal system of extractors. To evaluate both output flux and uniformity of the illuminance distribution of an extensive set of solutions, we wrote a Simulation Software Extractor Position (SISEPO). SISEPO was tested to optimise the extractor sequence of the initial HLG and a 15% improvement of the mean floor illuminance was predicted. The corresponding measured values were in good agreement and also the measurements of the luminous intensity distributions of the whole HLG-luminaire (EULUMDATA), carried out in individual segments of one meter length, confirmed the improvement of the light extraction efficiency.

Mixing rods are used in illumination systems to provide a uniform output. The use of separate sources, especially RGB LEDs, has renewed interest in the use of mixing rods. This paper describes some of the special issues that arise with the use of RGB LEDs. Issues discussed include die layout for RGB LED arrays, straight round mixers with ripples and RGB LEDs, the use of a diffusers with mixers, and the use of a square to rectangular mixer with ripples to circularize the mixer's angular output.

Light emitting diodes (LED) have been increasingly used as light sources for projection display. LEDs have numerous advantages as a light source for these applications especially when used with a digital micro-mirror spatial light modulator such as the device offered by Texas Instruments. LEDs create an expanded color gamut, they can be modulated at very high rates (thus, eliminating the need for a color wheel), and they last longer than other light sources. One disadvantage they have is the luminous output is lower than would be desired for most front projection applications. Smaller pocket projectors have used the LED sources successfully, but the luminous output is limited to between 25 and 100 lumens. One of the areas of light loss in the illumination system is in the multiplexer that combines the three colored LEDs into a coaxial illumination beam. In this paper, this loss is quantified and an alternate multiplexer design is proposed.

To compete with and to surpass the performance of traditional lighting systems, white LED development is still facing the necessity of further improvements. An important topic that has to be addressed in this context is the spatial homogeneity of the white light emitted, an issue that is directly associated with the geometry and the composition of the color conversion elements (CCE) in phosphor converted LEDs. In order to avoid the need for experimental realization and inspection of a large number of different configurations and compositions, optical simulation provides a time- and cost saving alternative. In this contribution we discuss a simulation procedure which allows us to predict optimized solutions for the CCEs in white LED light sources. The simulation process involves the set-up of a model for the blue emitting LED chip and the implementation of a multitude of different geometries and compositions of individual CCEs on top of the chip. Since the light is scattered within the CCEs, the respective scattering model, which considers the phosphor particle size distribution and the phosphor weight fraction is of particular importance. In the final sequence of the modeling procedure color uniformity is checked by monitoring the irradiance distributions both for the blue LED light and the yellow converted light separately on a detector. From a comparison of the simulation results for a significant number of different layouts we can deduce the impact of the individual materials parameters and predict optimized CCEs which are finally compared with real device set-ups in order to verify the accuracy of the simulation procedure.

The importance of condenser optics is the fact that it is the bottleneck limiting efficiency in commercially available projection systems. Conventional condensers use rotational symmetric devices, most of them being elliptic or parabolic mirrors. They perform very far from the theoretical limits for sources such as arc lamps or halogen bulbs. Typical small displays in the 5-15 mm² etendue range have geometrical efficiencies about 40-50% for the best condensers; although theory allows about 100% (no reflection nor absorption losses are considered). The problem is in the coma aberration of the reflectors and the rotational symmetric image of the source making the source projected image to unfit with the target. Thus, the only way to improve this performance is to generate a free form design that is able to control the shape and rotation of the source projected images. As yet, this can only be done with the SMS3D design method. We present here one of such designs achieving a collection efficiency 1.8 times that of an elliptical condenser for a 4:1 target aspect ratio and for the range of target etendue with practical interest and 1.5 for 16:9 target. These designs use only 1 additional reflection, i.e., use a total of 2 reflections from the source to the target. A prototype of one type of free form condenser has already been built.

As first generation extreme ultraviolet lithography (EUVL) systems go into the hands of lithographers, the obstacles to full production are reducing in number and scope. Chief among these remaining obstacles, however, is the source power. Although source manufacturers have made remarkable recent progress, power levels are still far below what is needed for production tools. This makes the importance of an efficient illumination system even more so as Moore's law pushes the industry to resolutions requiring EUVL. This paper describes some of the special issues for EUVL illumination systems, discusses several modeling tools appropriate to EUVL illumination systems, with examples based on fly's eye and debris mitigation systems found in the literature.

Discharge lamps serve a wide variety of applications and outperform novel light sources such as LEDs in terms of luminous flux and luminance. Unfortunately, such lamps occasionally show arc movements (flicker) which change the amount of light that is coupled into an optical system. A variety of measures in lamp design can suppress flicker tendencies of a lamp but arc movement cannot be totally avoided. In our contribution, we show that the way how the light is collected considerably influences the impact of flicker on the collected luminous flux. We investigate light collection sensitivity of an illumination system as a function of the etendue and of the particular realization of the illumination system. As a result, flicker sensitivity can be substantially reduced at the expense of collection efficiency.

Plastic Optical Fibres (POF) were developed almost 3 decades ago. They are mainly used for short haul data communications (up to 1 km with data rates up to 1 Gbps). Over the years, POF has found applications in many other areas including solar energy transport for illumination. In such an application, light is collected from the sun and is directed into a space which needs to be illuminated. The use of fibres and more specifically POF, in daylighting systems, started only a few years ago. Several approaches have been investigated and we have seen the development of a few commercial products. The market however, has not really taken off for these technologies simply because of their enormous price tags. It is important to note that the use of POF in these designs has been limited to the function of POF as the transmission medium only. We propose a novel solar illumination technique using POF as both the light collecting/concentrating mechanism and the transmission medium. By modifying the structure of the fibre, solar light can be directed into the fibre by using an analogous process to fibre side emission but, in the reverse. We shall report on the solar light capturing efficiency of POF as modified by several types of external imperfections introduced onto the fibre. One major advantage of our proposed approach lies in the fact that we aim to eliminate at least one of the two axes of sun tracking that is currently used in existing solar illumination systems.

An innovative optical panel provided with an hexagonal array of refractive lenses having a properly optimized doublecurvature profile has been simulated by ray-tracing and fabricated by injection-moulding. Such lenses are constituted by a concave profile (having negative curvature radius) on their bottom and a convex profile (having positive curvature radius) on their top. We demonstrate that, if compared to refractive elements with conventional geometry, bell-shaped microlenses allow to collect incident rays within a wider angular range (so reducing the number of rays lost by TIR ) and to properly re-direct them. When installed on fluorescent tubes-based professional lighting systems, such refractive elements allow to reduce undesirable glare as prescribed by EN12464-1 Interior Lighting Design Standards and to finely control photometric outputs of luminaries. Besides, bell-shaped microlenses-based films were also simulated to be applied onto a bottom-emitting lambertian OLED. We demonstrate that, by properly tailoring both concave and convex profile shape, it is possible to increase the outcoupling efficiency, as well as the luminous flux emitted by the exit surface, by a factor up to 1.95 and, at the same time, to produce far-field photometric outputs characterized by uniform isocandela distribution maps with an aperture angle up to 60°.

Light beam distortion from multiple reflections inside a luminaire is corrected by adding simple curvatures to different reflective surfaces, separating the management of the vertical and horizontal components of the beam. The luminaire directs the beam into the trajectory and convergence angle required for a digital ophthalmoscope, with a particular task of maximizing the contrast ratio in the image by reducing visible corneal reflectance of the light source.

The Köhler illumination concept was originally invented to achieve uniform illumination in microscopy¹. Köhler integrators can also be formed by arrays of lenticulations that can be any combination of reflective and/or refractive surfaces, organized in corresponding pairs. Arrays of integrating facets can be arranged not only on flat surfaces but on rotationally symmetric and even freeform surfaces⁶. Currently flat lenslet arrays are widely applied as homogenizing optics² for lithography, machine vision illumination, and projection. Adding Köhler facets onto already designed surfaces can improve the optical system performance, while respecting its original function. In general, the optics output can be made somewhat independent of the source characteristics, although at the expense of a slight ètendue dilution or efficiency losses. This work revises the Köhler concept and its application to different kind of optics, ranging from photovoltaic concentrators to automotive LED headlights. In the former, irradiance peaks on the solar cell can be avoided, while preserving high aiming tolerance (acceptance) of the solar concentrator. In the latter, LEDs drawbacks like large source image sizes, source misalignments, ill defined source edges, and low source radiance can be compensated.

Applications requiring high lumen packages are traditional the domain of light sources like discharge lamps. Currently, LEDs make their way into such applications. LED street lighting projects, which are regularly covered in the press, provide a case of point. Life time and luminous efficacy are considered as being the main advantages of LEDs. Nonetheless, other current light sources for street lighting have similar performance. Analysing a street-lamp as a complete system, we can show that LED solutions have significant advantages if highly efficient optics are used. We present an example with tailored free-form optics. These make efficient use of the valuable LED light by exactly redistributing it into the desired illuminance pattern.

Reflectors for prescribed intensity or illuminance distributions are commonly used in luminaires and automotive headlights. However, their design has remained a challenge. Although reflector shapes are well known for a point source, the point source approximation leads to significant errors in the output distribution with extended and nonuniform source distributions. In practice, source non-idealities usually require the use of automated and manual optimization in the design process. We propose a hybrid optimization scheme that generates reflector shapes for rotationally symmetric systems and an arbitrary source luminance distribution. This method is based on an extension of the traditional algorithm for a point source, and uses a combination of an iterative algorithm and an optimization algorithm. Several case studies are presented.

A white light source, based on illumination of a yellow phosphor with a fibre-coupled blue-violet diode laser, has been designed and built for use in endoscopic surgery. This narrow light probe can be integrated into a standard laparoscope or inserted into the patient separately via a needle. We present a Monte Carlo model of light scattering and phosphorescence within the phosphor/silicone matrix at the probe tip, and measurements of the colour, intensity, and uniformity of the illumination. Images obtained under illumination with this light source are also presented, demonstrating the improvement in illumination quality over existing endoscopic light sources. This new approach to endoscopic lighting has the advantages of compact design, improved ergonomics, and more uniform illumination in comparison with current technologies.

The purpose of the secondary optical design for light emitting diodes (LED) illumination is to rearrange the direct output of LED and then achieve the desired illumination. Usually a lens is applied to realize this function in an LED illumination system, and a freeform lens can do better than the traditional spherical ones. The method in this paper can be used to design a freeform lens in short time, just less than 10 seconds. And this freeform lens is constructed using the numerical solutions of a set of first-order partial differential equations, which are deduced from the Snell's law according to the conservation of energy. Using an LED as the source while immersing it in the lens, a uniform rectangle can be gotten through single refraction, and with uniformity near to 90%. The rectangular illumination also has a relatively clear cut-off line with little blur at the edge. This method can shorten the designing time and improve the performance of LED illumination system. Furthermore, not only rectangle, but other illumination figures can be achieved by freeform lens designed by this method, which can broaden the scope of freeform lens's usage.

This paper develops a design method of the prism pattern for a LCD light guide plate to improve the uniformity of its exiting light. Firstly, the LGP prism surface is divided into several equal regions. With the aid of ASAP simulation, this method uses the mean light flux of all regions as a reference value to adjust the distribution density of the prism pattern for each region. Then curve fitting is performed to provide a smoothly changing distribution density for further improve-ment of the exiting light uniformity. ASAP results demon-strate that illuminance uniformity for the study case is sub-stantially improved from 45% to 90.9% by using this design method.