In this work, we demonstrate how it is possible to sharply image multiple object points. The Simultaneous Multiple Surface (SMS) design method has usually been presented as a method to couple N wave-front pairs with N surfaces, but recent findings show that when using N surfaces, we can obtain M image points when N<M under certain conditions. We present the evolution of SMS method, from its basics, to imaging two object points through one surface, the transition from two to three objet points obtained by increasing the parallelism, and getting to the designs of six surfaces imaging up to eight object points. These designs are limited with the condition that the surfaces cannot be placed at the aperture stop. In the process of maximizing the object points to sharp image, we try to exhaust the degrees of freedom of aspherics and free-forms. We conjecture that maximal SMS designs are very close to a good solution, hence using them as a starting point for the optimization will lead us faster to a final optical system. We suggest here different optimization strategies which combined with the SMS method are proven to give the best solution. Through the example of imaging with the high aspect ratio, we compare the results obtained optimizing the rotational lens and using a combination of SMS method and optimization, showing that the second approach is giving significantly smaller value of overall RMS spot diameter.

The spatial coherence of solar beam radiation is a key constraint in solar rectenna conversion. Here, we present a derivation of the thermodynamic limit for coherence-limited solar power conversion – an expansion of Landsberg’s elegant basic bound, originally limited to incoherent converters at maximum flux concentration. First, we generalize Landsberg’s work to arbitrary concentration and angular confinement. Then we derive how the values are further lowered for coherence-limited converters. The results do not depend on a particular conversion strategy. As such, they pertain to systems that span geometric to physical optics, as well as classical to quantum physics. Our findings indicate promising potential for solar rectenna conversion.

The Floquet theory and the transfer-matrix approach were used to investigate the excitation of surfaceplasmon-polariton (SPP) waves and waveguide modes in a structure comprising a one-dimensional photonic crystal (1D PC) of finite thickness on top of a planar thick metallic layer. The solutions of the relevant dispersion equations were used to predict the excitation of multiple SPP waves and waveguide modes when the metallic layer is patterned as a two-dimensional (2D) surface-relief grating. The same structure was experimentally fabricated and optically characterized to validate the theoretical approach. Both the theoretical and experimental results show broadband coupling of incident light of either linear polarization state over a broad range of the angle of incidence. This structure has potential applications in planar optical concentrators.

Structural color is produced when nanostructures called schemochromes alter light reflected from a surface through different optic principles, in contrast with other types of colors that are produced when pigments selectively absorb certain wavelengths of light. Research on biogenic photonic nanostructures has focused primarily on bird feathers, butterfly wings and beetle elytra, ignoring other diverse groups such as spiders. We argue that spiders are a good model system to study the functions and evolution of colors in nature for the following reasons. First, these colors clearly function in spiders such as the tarantulas outside of sexual selection, which is likely the dominant driver of the evolution of structural colors in birds and butterflies. Second, within more than 44,000 currently known spider species, colors are used in every possible way based on the same sets of relatively simple materials. Using spiders, we can study how colors evolve to serve different functions under a variety of combinations of driving forces, and how those colors are produced within a relatively simple system. Here, we first review the different color-producing materials and mechanisms (i.e., light absorbing, reflecting and emitting) in birds, butterflies and beetles, the interactions between these different elements, and the functions of colors in different organisms. We then summarize the current state of knowledge of spider colors and compare it with that of birds and insects. We then raise questions including: 1. Could spiders use fluorescence as a mechanism to protect themselves from UV radiation, if they do not have the biosynthetic pathways to produce melanins? 2. What functions could color serve for nearly blind tarantulas? 3. Why are only multilayer nanostructures (thus far) found in spiders, while birds and butterflies use many diverse nanostructures? And, does this limit the diversity of structural colors found in spiders? Answering any of these questions in the future will bring spiders to the forefront of the study of structural colors in nature.

Free-form reflectors are encountered in numerous illumination systems, especially in highly sophisticated applications. The construction of these kind of optics however remains a challenging task where only a few methods are available to derive the free-form shape. One such method is the multi-ellipse approach where a superposition of conic sections is utilized to create the desired illuminance or luminous intensity distribution. While it is useful in many areas one is not always interested in an illuminance or intensity distribution. Especially street lighting reflectors are often tailored towards a homogeneous luminance, taking into account the road's reflective properties, luminaire arrangement etc. While we used our implementation of the multi-ellipse method to design street lighting reflectors with a uniform illuminance before, we now extended this method to support the calculation of a roadway reflector with a homogeneous luminance. For a given roadway scenario we can quickly get an optimized reflector with a good performance compliant to roadway standards such as EN-13201 or IESNA-RP-8-00. Furthermore the optic can be quickly adapted to changing requirements.

In this paper we list a few problems in nonimaging optics which we believe are fundamental to further development of the subject. It is our hope that as they are solved, and crossed of the list, further progress can be facilitated.

Aplanats make great concentrators because of their near perfect imaging. Aplanatic conditions can be satisfied using two surface curves (generally mirrored surfaces) in two dimensions (see Figure 1) which are constructed by successive approximation to create a highly efficient concentrator for both concentration and illumination. For concentration purposes, having a two mirror system would be impossible because the front mirror would block incoming light (see figure 2) so the idea is to replace the front mirror with a "one-way" mirror. Light from a lower index can be transmitted, so if the aplanat surface is a higher index light is allowed to enter, and be trapped. In the Jellyfish design, TIR takes place except for light striking the surface within the range of critical angles. To combat that, a small area of reflective coating is applied to the central top part of the Jellyfish, where TIR fails (In the middle) to keep the light there from directly escaping (see figure 3). The design works in both forwards and reverse. Light entering can be focused to a collecter, or the collecter can be replaced with a light source to concentrate light out. In this case, LEDs are used for their highly efficienct properties.

One of the world’s oldest civilizations – with the worst air pollution and the coldest capital city – will employ cutting-edge technology from the newest UC campus starting in February. Professor Roland Winston, who leads the UC Merced-based UC Solar Institute, just returned from a trip to Ulaanbaatar (UB), Mongolia’s capital. He met with the owner of Mongolia National University (MNU), a 15-yearold institution with about 9,000 students, to discuss installing a solar-thermal unit on one of the campus buildings to generate 3 kilowatts of steam heat for a portion of the campus

In this article we discuss an emerging concept for non-mechanical solar tracking that can have a significant impact for the design of next generation concentrator photovoltaics systems. Based on the modification of the optical properties of the concentrator elements instead of their mechanical rearrangement, self-tracking concentrators, with recently demonstrated prototypes, could make the mechanical trackers redundant expanding the scope of application of CPV systems. We propose here a new approach to a reactive-tracking system, analyze its underlying physics and discuss initial experimental and simulation results towards the development of a prototype.

Enhancing solar cell conversion efficiency by angular confinement of radiative emission (photoluminescence) requires a combination of (1) high external luminescent efficiency, and (2) optics that can substantially and efficiently limit the angular range of cell luminescence. After covering the basic principles and recent proposals for suitable micro-optics, we investigate an assortment of alternative micro-optical designs that can improve device compactness considerably, which would reduce the amount of material required and would ease micro-fabrication, while offering liberal optical tolerance and high collection efficiency.

A novel non-imaging micro-concentrator concept and its development in Sandia National Lab’s microsystems-enabled photovoltaics (MEPV) program are described in this paper. Key notions of the compact 2-element optical concentrator are toroidal lens surfaces that decentralize the focused beam and a reflective cone structure that enhances light collection and illumination onto micro-scale solar cells (e.g., ~100’s microns in diameter). The optical configuration therefore provides a low-intensity, hot-spot-free illumination pattern on the receiver while achieving a concentration-acceptance angle product (CAP) over 1. Designs taking into account practical factors (such as fabrication capabilities, misalignments) achieve a 400X geometric concentration with a ±2.4° (90% of peak) acceptance angle (CAP = 0.84) and a 600X geometric concentration with a ±2° acceptance angle (CAP = 0.85), allowing low cost, mass production using injection molding. Development and experimental evaluation of a baseline prototype module is also described.

A spectrum splitter can be used to spatially multiplex different solar cells that have high efficiency in mutually exclusive parts of the solar spectrum. We investigated the use of a surface-relief grating made of dielectric materials for specularly transmitting one part of the solar spectrum while the other part is transmitted nonspecularly and the total reflectance is very low. A combination of (i) the rigorous coupled-wave approach for computing the reflection and transmission coeffients of the grating and (ii) the differential evolution algorithm for optimizing the grating shape was devised as a design tool. We used this tool to optimize two candidate gratings and obtained denite improvements to the initial guesses for the structural and constitutive parameters. Signicant spectrum splitting can be achieved if the angle of incidence does not exceed 15.

We have evaluated a new concept for a variable light valve and thermal insulation system based on nonimaging optics. The system incorporates compound parabolic concentrators and can readily be switched between an open highly light transmissive state and a closed highly thermally insulating state. This variable light valve makes the transition between high thermal insulation and efficient light transmittance practical and may be useful in plant growth environments to provide both adequate sunlight illumination and thermal insulation as needed. We have measured light transmittance values exceeding 80% for the light valve design and achieved thermal insulation values substantially exceeding those of traditional energy efficient windows. The light valve system presented in this paper represents a potential solution for greenhouse food production in locations where greenhouses are not feasible economically due to high heating cost.

Employing optical fibres for transferring concentrated radiation from solar concentrators has potential advantages in terms of transmission energy efficiency, technical feasibility and cost-effectiveness compared to a conventional heat transfer system employing heat exchangers and a heat transfer fluid. The basic investigated system comprised a broadband source, collimator lens, objective lens and optical fibre as the carrier of energy to the receiver. The relationship between transmission and length of fibre is studied via simulation using the ray tracing model, LightTools®. Two different sources were defined in the system setup including a white light source and the solar simulator with similar spectral distribution as solar spectrum. The effects on transmission of varying the hydroxyl content, and the core size of the fibres are also investigated experimentally. The experimental results are then compared with simulations. The initial results indicate that the selected low OH unjacketed bulk fibre with NA=0.22 is capable of transmitting approximately 92% of the concentrated solar energy over lengths up to 10 m with less loss compared to conventional methods for direct transferring of concentrated solar radiation.

Solar optical modeling tools are valuable for modeling and predicting the performance of solar technology systems. Four optical modeling tools were evaluated using the National Solar Thermal Test Facility heliostat field combined with flat plate receiver geometry as a benchmark. The four optical modeling tools evaluated were DELSOL, HELIOS, SolTrace, and Tonatiuh. All are available for free from their respective developers. DELSOL and HELIOS both use a convolution of the sunshape and optical errors for rapid calculation of the incident irradiance profiles on the receiver surfaces. SolTrace and Tonatiuh use ray-tracing methods to intersect the reflected solar rays with the receiver surfaces and construct irradiance profiles. We found the ray-tracing tools, although slower in computation speed, to be more flexible for modeling complex receiver geometries, whereas DELSOL and HELIOS were limited to standard receiver geometries such as flat plate, cylinder, and cavity receivers. We also list the strengths and deficiencies of the tools to show tool preference depending on the modeling and design needs. We provide an example of using SolTrace for modeling nonconventional receiver geometries. The goal is to transfer the irradiance profiles on the receiver surfaces calculated in an optical code to a computational fluid dynamics code such as ANSYS Fluent. This approach eliminates the need for using discrete ordinance or discrete radiation transfer models, which are computationally intensive, within the CFD code. The irradiance profiles on the receiver surfaces then allows for thermal and fluid analysis on the receiver.

Cities and towns around the world are becoming more condensed due to the shrinking amount of buildable areas, which significantly reduces the amount of light that occupants have access to. This lack of natural lighting results in health, safety and quality of life degradation. This paper presents a new technique of transmitting sunlight downward into narrow alleys and streets, by using a daylighting guiding acrylic panel that is capable of changing the direction and distribution of the incident light. The core of the proposed daylight guidance system is made up of light transmission panels with high quality. The corrugations have sine wave shaped cross-section so that the panel functions as an optical diffuser perpendicular to the direction of sunlight propagation. The day lighting system consists of the corrugated panels and a lattice frame, which supports the panel. The proposed system is to be mounted on the building roof facing the sun so as to redirect the incident sunlight downward into the narrow alleys or streets. Since building sizes and orientations are different the frame is arranged such that substantially deep light penetration and high luminance level can be achieved. Simulation results show that the proposed panel improves the illuminance values by more than 200% and 400% in autumn and winter, respectively, provides fan-out angle that exceeds 80° for certain solar altitudes and the transmitted power percentage varies from 40% to 90% as the solar altitude varies from 10° to 80°. Experimental results are in a good agreement with the simulations.