This PDF file contains the front matter associated with SPIE Proceedings Volume 8124, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

To date, the lack of light delivery mechanisms to the oral cavity remains a barrier to the treatment of oral cancer with photodynamic therapy (PDT). The greatest impediment to medical practitioners is the current need to shield the normal tissues of the oral cavity, a costly and time-consuming procedure. In this research, we present the design of illumination devices to deliver light to the oral cavity for PDT, which will facilitate administration of PDT in the clinic. The goal for such an illumination device, as indicated by our clinical collaborators at Roswell Park Cancer Institute in Buffalo, NY, is to limit exposure of healthy tissue and produce an average irradiance of 100 mW/cm² over the treatment field, with spatial non-uniformities below 10%. Furthermore, the size of the device must be compact to allow use in the oral cavity. Our research led to the design and fabrication of two devices producing spatial non-uniformities below 6% over a treatment area of 0.25 cm² by design. One device consisted of an appropriately-sized reflector, inspired by solar concentrators, illuminated by a cylindrical diffusing fiber optimally located within the reflector; another was a solid lightpipe with a combination of optimized tapered and straight components.

Freeforms in illumination systems are directly constructed by adapting some ideas of Oliker and co-workers [1]. The freeform is created by a set of primitive surface elements which are generalized Cartesian ovals including the optical response of the residual system. Hamiltonian theory of ray optics can be used to determine the family of primitives which is in particular a simple task if the freeform is the exit surface of the illumination system. For simple optical systems an analytical description of the primitives is possible. Contrarily, for more complex optics a conventional raytracer is additionally utilized to determine the required system's information, like the optical path lengths or mixed characteristics. To this end a discrete set of rays is traced through the residual systems and the required relations are interpolated to obtain a quasi-analytic representation of the primitives. The potential of this approach is demonstrated by some examples, e.g. freeform optics including collimating or deflection elements.

A metal-less RXI collimator has been designed. Unlike to the conventional RXI collimators, whose back surface and central part of the front surface have to be metalized, this collimator does not include any mirrored surface. The back surface is designed as a grooved surface providing two TIR reflections for all rays impinging on it. The main advantage of the presented design is lower manufacturing cost since there is no need for the expensive process of metalization. Also, unlike to the conventional RXI collimators this design performs good colour mixing. The first prototype of V-groove RXI collimator has been made of PMMA by direct cutting using a five axis diamond turning machine. The experimental measurements of the first prototype are presented.

The increasing demands for non-self-emissive portable display devices jointly stimulate the needs for additional front light units to provide extra illumination to compensate for the ambient light in dim environment. The advantages of light emitting diodes (LED), such as high efficiency and small size, make it an ideal source for the compact unit, but direct LED lighting is impractical. Secondary optics is commonly adopted in illumination occasions to ensure the output from the LED dies meet the overall specification. Considering an oblique incidence situation, light mapping redistribution is inevitable. In this paper, we propose a beam shaping method adopting microlens array with various focal length to achieve uniform light distribution. The design is based on edge ray principle, which considers each microlens individually. Microlenses with various focuses were made by photoresist thermal reflow process to verify the novel design.

The hybrid SMS-DSF method of nonimaging optical design combines the discrete simultaneous multiple surface (SMS) method with the dual-surface functional (DSF) method to obtain improved optical performance relative to the discrete SMS method alone. In this contribution we present a new extension of the hybrid SMS-DSF method that uses differential ray tracing to produce designs having significantly improved performance relative to the original hybrid SMS-DSF method.

The tantalizing prospect of using antennae for solar power conversion received preliminary consideration, but was not pursued in earnest due to the daunting challenges in suitable materials, fabrication procedures, and the rectification (conversion to DC power) of frequencies approaching 1 PHz (10¹⁵ s^-1). Recent advances in nano-materials and nano-fabrication technologies have prompted revisiting the solar antenna strategy. Coherence theory informs us that even ostensibly incoherent radiation is partially coherent on a sufficiently small scale. Based on a generalized broadband analysis, we show how the partial coherence of sunlight, exhibiting transverse partial coherence on a scale of two orders of magnitude larger than its characteristic wavelengths, impacts the potential of harvesting solar energy with aperture antennae (coherent detectors), and establish a fundamental bound. These results quantify the tradeoff between intercepted power and averaged intensity with which the effect of increasing antenna size (and hence greater system simplicity) can be evaluated.

Nonimaging Optics is the theory of thermodynamically efficient optics and as such depends more on thermodynamics than on optics.

Certain classes of gradient-index lenses can achieve both perfect imaging and flux concentration at the fundamental limits. Although useful in microwave technology, eponymous Luneburg lenses have been viewed as esoteric idealizations for visible and near-infrared radiation due to the paucity of suitable materials and fabrication methods. We show that the classic Luneburg problem was constrained in subtle, implicit ways that can be relaxed. With the extra degrees of freedom, we demonstrate new gradient-index profiles that can accommodate both realistic, readily available materials and existing manufacturing technologies, while compromising neither perfect imaging nor maximum concentration (confirmed by raytrace simulation) - thereby opening new vistas for solar concentration and other visible and near-infrared applications. Specifically, the broader genres of solutions identified here permit a far smaller range of refractive indices than previously believed, with minimum required refractive index values well above unity, at arbitrary lens f-number, with less sensitivity to dispersion losses than conventional lenses.

This paper discusses the development, deployment and operation of the optical waveguide (OW) solar thermal power system for In-Situ Resource Utilization (ISRU) applications at the NASA ISRU analog test site on Mauna Kea, HI. In this solar thermal system, solar radiation is collected by the concentrator array which transfers the concentrated solar radiation to the OW transmission line made of low loss optical fibers. The OW transmission line directs the solar radiation to the place of utilization of the solar energy. In this paper applications of solar energy to sintering of native soil for surface stabilization and thermo-chemical processing of native soil for oxygen production are discussed.

Manufacturing technologies as injection molding or embossing specify their production limits for minimum radii of the vertices or draft angle for demolding, for instance. In some demanding nonimaging applications, these restrictions may limit the system optical efficiency or affect the generation of undesired artifacts on the illumination pattern. A novel manufacturing concept is presented here, in which the optical surfaces are not obtained from the usual revolution symmetry with respect to a central axis (z axis), but they are calculated as free-form surfaces describing a spiral trajectory around z axis. The main advantage of this new concept lies in the manufacturing process: a molded piece can be easily separated from its mold just by applying a combination of rotational movement around axis z and linear movement along axis z, even for negative draft angles. Some of these spiral symmetry examples will be shown here, as well as their simulated results.

Transmission gratings that combine a large diffraction angle with a high diffraction efficiency and low angular and wavelength dispersion can be used to concentrate sunlight in a light guide and for lighting applications. Surface-relief gratings with sub-wavelength grating periods can have these properties. In this paper we study their diffraction efficiency for general conical angles of incidence. We show the presence of regions in the space of incident angles where light is efficiently coupled into or out of total internal reflection. It is demonstrated how this distribution of the diffraction efficiency over angular space can be adjusted by changing the grating geometry. Finally, these properties are qualitatively verified using holographically produced surface relief gratings.

Optics with high optical efficiency and reliability are the key components for CPV modules as well as high efficiency solar cells and a high accuracy tracker. The present paper describes the optical design, simulation and materials, including a direct comparison of geometrically identical lens designs for different materials i. e. PMMA (or acrilic) and silicone-on-glass (SOG) respectively, and glass secondary in three different geometries. The Fresnel lenses manufactured as 5×4 monolithic parquets are called Triple Primaries, and serve as test samples and off-the-shelf products of Concentrator Optics GmbH.

Within a detailed balance formalism, the open circuit voltage of a solar cell can be found by taking the band gap energy and accounting for the losses associated with various sources of entropy increase. Often, the largest of these energy losses is due to the entropy associated with spontaneous emission. This entropy increase occurs because non-concentrating solar cells generally emit into 2π steradian, while the solid angle subtended by the sun is only 6.85×10^-5 steradian. Thus, for direct normal irradiance, non-concentrating solar cells with emission and acceptance angle limited to a narrow range around the sun could see significant enhancements in open circuit voltage and efficiency. With the high degree of light trapping we expect given the narrow acceptance angle and the ray optics brightness theorem, the optimal cell thickness will result in a discrete modal structure for most materials. Thus, limiting the acceptance and emission angle can be thought of as coupling to only a subset of radiating modes, or, alternatively, as altering the modal structure such that some radiating modes become bound modes. We have shown the correspondence between the ray optics picture and the modal picture, by deriving the ray optics results for light trapping under angular restrictions using a modal formulation. Using this modal formulation we can predict the light trapping and efficiencies for various thin structures under angular restriction. We will discuss these predicted efficiencies and various options for implementing broadband and angle-specific couplers.

We explore the use of light scattering off diffuser elements to enhance the collection efficiency in a passive solar collection system. Our work is focused on establishing the link between the scattering surface profile and the angular distribution of the scattered radiation. We have carried out such studies through simulations using ASAP® software and are currently working on comparing the results with experimentally obtained data.

Development of a novel HCPV nonimaging concentrator with high concentration (>500x) and built-in spectrum splitting concept is presented. It uses the combination of a commercial concentration GaInP/GaInAs/Ge 3J cell and a concentration Back-Point-Contact (BPC) silicon cell for efficient spectral utilization, and external confinement techniques for recovering the 3J cell's reflection. The primary optical element (POE) is a flat Fresnel lens and the secondary optical element (SOE) is a free-form RXI-type concentrator with a band-pass filter embedded in it - Both the POE and SOE performing Köhler integration to produce light homogenization on the receiver. The band-pass filter transmits the IR photons in the 900-1200 nm band to the silicon cell. A design target of an "equivalent" cell efficiency ~46% is predicted using commercial 39% 3J and 26% Si cells. A projected CPV module efficiency of greater than 38% is achievable at a concentration level larger than 500X with a wide acceptance angle of ±1°. A first proof-of concept receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ~100x and lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using a 3J cell with a peak efficiency of 36.9%.

Novel solutions for realistic gradient-index (GRIN) lenses are presented, that create the possibility of nominally stationary photovoltaic concentrators capable of daylong averaged flux concentration levels of order 10³. One transfers the burden of precision solar tracking from massive units on which numerous solar modules are mounted, to miniaturized mechanical components inside modules that are completely stationary. The best optical properties for this aim would appear to be perfect imaging - a case where imaging and nonimaging objectives coalesce because perfect imaging is non-trivially synonymous with attaining the fundamental limit to concentration. Our GRIN profiles surmount limitations of classical Luneburg solutions that resulted in GRIN lenses being deemed physically unattainable idealizations for sunlight. To wit, while preserving perfect imaging, our GRIN profiles eliminate the need for refractive indices near unity, markedly reduce the range of refractive indices required, and permit arbitrary focal length. They are also amenable to realistic materials and fabrication technologies. Raytrace simulations confirm that they offer an unprecedented solution to this problem - even accounting for chromatic aberration and misalignment. Eliminating massive precision tracking of large photovoltaic arrays in favor of precision cm-scale lens tracking inside the modules opens the possibility of rooftop CPV. The perception that high solar concentration is inseparably linked to massive trackers is supplanted here by a different paradigm.

Metal grid lines are a vital element in multijunction solar cells in order to take out from the cell the generated photocurrent. Nevertheless all this implies certain shadowing factor and thus certain reflectivity on cells surface that lowers its light absorption. This reflectivity produces a loss in electrical efficiency and thus a loss in global energy production for CPV systems. We present here an optical design for recovering this portion of reflected light, and thus leading to a system efficiency increase. This new design is based on an external confinement cavity, an optical element able to redirect the light reflected by the cell towards its surface again. It has been possible thanks to the recent invention of the advanced Köhler concentrators by LPI, likely to integrate one of these cavities easily. We have proven the excellent performance of these cavities integrated in this kind of CPV modules offering outstanding results: 33.2% module electrical efficiency @Tcell=25ºC and relative efficiency and I_sc gains of over 6%.

Dual-mirror aplanatic optics - recently developed for concentrator photovoltaics - can offer efficient, ultra-compact, high-irradiance solar concentration. However, intrinsic limitations site the focus inside the concentrator and hence engender a dielectric terminal concentrator to deliver the concentrated radiation to the photovoltaic cell outside the optic, with the associated requirement of an optical bond to the cell. Can a modification in the design strategy place the focus outside the optic - and hence obviate the need for a terminal concentrator and optical bond - without compromising compactness, low shading losses, or even the practical virtue of the primary and secondary mirrors being coplanar toward easing optical component alignment? We show how nested dual-mirror aplanats can satisfy all these goals, supported by raytrace performance evaluations.

In this work the concept of integrating tracking in concentrating photovoltaics is briefly summarized and possible fields of application are classified. A previously proposed system setup relies on the use of two rotational symmetric laterally moving plano-convex lenses to achieve 500× concentration over an angular range of ±24°. However, the circular lens apertures are less suitable for application in lens array structures. A new design algorithm based on the Simultaneous Multiple Surface algorithm in three dimensions (SMS3D) demonstrates the ability to address this problem. Performance simulations show that the resulting non-rotational symmetric design outperforms its conventional rotational symmetric counterpart.

A novel nonimaging focusing heliostat consisted of many small movable element mirrors that can be dynamically maneuvered in a line-tilting manner has been proposed for the astigmatic correction in a wide range of incident angle from 0° to 70°. In this article, a comprehensive optical characterization of the new heliostat with total reflective area of 25 m² and slant range of 25 m using ray-tracing method has been carried to analyze the performance including solar concentration ratio, ratio of aberrated-to-ideal image area, intercept efficiency and spillage loss. The optical characterization of the heliostat in the application of solar power tower system has embraced the cases of 1×1, 9×9, 11×11, 13×13, 15×15, 17×17 and 19×19 arrays of concave mirrors provided that the total reflective area remains the same. The simulated result has shown that the maximum solar concentration ratio at a high incident angle of 65° can be improved from 1.76 suns (single mirror) to 104.99 suns (9×9 mirrors), to 155.93 suns (11×11 mirrors), to 210.44 suns (13×13 mirrors), to 246.21 suns (15×15 mirrors), to 259.80 suns (17×17 mirrors) and to 264.73 suns (19×19 mirrors).

Organic luminescent solar concentrators (LSCs) have been widely investigated due to their potential in dramatically decreasing the cost of collecting solar energy. We designed, fabricated organic LSCs at different sizes and characterized their optical and electrical properties. The output efficiency enhancement methods for LSCs photovoltaics (PVs) are explored including attaching white diffusers on the bottom surfaces of LSCs, and adding a refractive index matched optical gel between the LSC edge surfaces and the attached PV cells. To further improve the output power conversion efficiency, multi-layered LSCs are studied and compared with single layered LSCs. The distribution of the output current from the LSC edges varies slightly, which is beneficial to collection of the concentrated light by attached PV cells. Also, in comparison with applying a wavelength selective film, the alignment of dye molecules using polymerized liquid crystal is discussed as a promising optical design and efficiency improvement method.

A novel solar furnace system has been proposed to be consisted of a Nonimaging Focusing Heliostat and a smaller parabolic concentrator. In this configuration, the primary heliostat consists of 11×11 array of concave mirrors with a total reflective area of 121 m² while the secondary parabolic concentrator has a focal length of 30 cm. To simplify the design and reduce the cost, fixed geometry of the primary heliostat is adopted to omit the requirement of continuous astigmatic correction throughout a year. The overall performance of the novel solar furnace configuration can be optimized if the heliostat's spinning-axis is fixed in the orientation dependent on the latitude angle so that the annual variation of incidence angle is the least, which ranges from 33° to 57°. Case study of the novel solar furnace system has been performed with the use of ray-tracing method to simulate solar flux distribution profile for two different target distances, i.e. 50 m and 100 m. The simulated results have revealed that the maximum solar concentration ratio ranges from 20,530 suns to 26,074 suns for the target distance of 50 m, and ranges from 40,366 suns to 43,297 suns for the target distance of 100 m.

Natural light is an inexhaustible and environmentally friendly energy. The solar energy exposed to the earth everyday is about three thousand times to the global energy consumption. Therefore, it would be a considerably large energy saving if we collect and guide the sunlight for lighting. Currently, there are two types of solar concentrators for collecting sunlight purpose, namely, active and static. The former is more efficient, but needs costly active sun-tracking system for supplement; the latter is cheaper, but is limited for certain time slots. In static systems, a hemispherical concentrator can gather the sunlight with longer time, but the collected flux is not stable and the energy density of optical fiber is lower than the illuminance of sunlight. We, in this paper, propose a hemispherical static concentrator that consists of double aspheric compensated lens array. The double layers of lenses are designed with large tolerance for continued collecting sunlight and the apertures of lenses are larger than optical fiber for increasing the energy density. According to the simulation results, we get uniform distribution of collected flux from 10 a.m. to 4 p.m. that is less than 10% change. Moreover, the energy density of optical fiber is about 50 Lm/cm² in summer when the illuminance of sunlight is about 120,000 Lux.

The study would investigate the effect of the scattering model on the photoelectric conversion efficiency for the silicon solar cell and dye-sensitized solar cell (DSSC). We will examine the accuracy of optical simulation of these solar cells by the A class standard measurement of AM1.5G at the light source of 1000 W/m². The scattering lighting of DSSC always is occurred by the particle size of the titanium dioxide (TiO₂) and the distribution of the layer. Anyway, the silicon solar cell would absorb the lighting by the energy band of the silicon. Therefore, the bidirectional scattering distribution function (BSDF) could descript the scattering status for the silicon solar cell and DSSC. The regular pattern of the cover glass including the type, size, deep and smooth would affect the scattering model of the silicon solar cell and DSSC for the absorption efficiency. We found the absorption efficiency would be enhanced at the scatter pattern of large deep and smooth. The scattering pattern in the front always was better than in the back for the cover glass at the efficiency of lighting absorption. The absorption efficiency of DSSC would be higher than the silicon solar cells at the same scattering pattern. The optical simulation and measurement results showing the absorption efficiency of DCCS was better than the efficiency of silicon solar cell.