This PDF file contains the front matter associated with SPIE Proceedings Volume 8485 including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Non-imaging Optics is the theory of thermodynamically efficient optics and as such depends more on thermodynamics than on optics. Hence in this paper a condition for the "best" design is proposed based on purely thermodynamic arguments, which we believe has profound consequences for design of thermal and even photovoltaic systems. This new way of looking at the problem of efficient concentration depends on probabilities, the ingredients of entropy and information theory while “optics” in the conventional sense recedes into the background.

CPV optics typically have multiple discrete apertures which each focus sunlight directly onto an associated PV cell. Waveguide based CPV systems instead couple light from multiple small apertures through a shared slab waveguide, avoiding individual optical alignment and electrical connection of multiple PV cells. We previously demonstrated the design and fabrication of a planar micro-optic waveguide concentrator, where incoming sunlight is focused through millimeter pitch lenslets onto mirrored micro-prisms which couple light into a slab waveguide toward common PV cells. This enables an efficient high concentrator system with a compact geometry. However, this design has the typical CPV limitation of low angular acceptance, requiring precise two-axis large-scale mechanical tracking. Here, we present the results of a design study to adapt the planar micro-optic design for use in combination with a one-dimensional mechanical tracker, tilted at latitude, to provide azimuthal alignment and altitude bias. Lateral mechanical micro-tracking can accommodate the residual altitude misalignment. The design shows that this relatively simple system can still provide over 72% annual optical efficiency for a 50x concentrator. Replacing the micro-tracking with passive optical altitude alignment further reduces system complexity, but also reduces efficiency. These waveguide based concentrators have primarily been designed for use with photovoltaic cells, which are index matched onto the waveguide either directly, or through output couplers. For concentrating solar power systems, sunlight is focused onto thermally isolated devices which can not be in direct contact. We will also present alternative output coupler designs, which allow extraction of light from the waveguide to an air or vacuum isolated coupler. The loss associated with these couplers is substantially identical to the reflection losses of one additional mirror.

In this work, a new design concept of SMS moving optics is developed, in which the movement is no longer lateral but follows a curved trajectory calculated in the design process. Curved tracking trajectory helps to broaden the incident angle’s range significantly. We have chosen an afocal-type structure which aim to direct the parallel rays of large incident angles to parallel output rays. The RMS of the divergence angle of the output rays remains below 1 degree for an incident angular range of ±45⁰. Potential applications of this beam-steering device are: skylights to provide steerable natural illumination, building integrated CPV systems, and steerable LED illumination.

Layer-multiplying coextrusion is a manufacturing technology capable of producing composite nanolayered opticalpolymer films having precisely controlled refractive-index distributions. This technology can be applied to the fabrication of spectral filters based on a variation of the Christiansen filter. The basic idea is to produce an optical component consisting of alternating films of two distinct polymer materials in optical contact, with textured interfaces between adjacent films. By designing the two materials to have refractive indices that are matched at a specific wavelength, such a component can produce significant light scattering for wavelengths far from the index-matched wavelength, with negligible scattering for wavelengths sufficiently close to that wavelength. We discuss the theory and characteristics of this new type of advanced spectral filter, present a number of potential applications, and provide design examples.

We present the design and simulation of first-ever planar single-element solar lenses (modified hemispherical gradientindex structures) for concentrator photovoltaic applications, with high collection efficiency and liberal optical tolerance at averaged cell irradiance levels exceeding 1000 suns. These compact lens designs satisfy the severe constraints of the refractive indices of viable polymeric materials and fabrication techniques, for visible and near-infrared radiation. The planar hemispherical gradient-index lens for a far-field (solar) source is created from a near-field unit magnification spherical gradient-index lens. Our new solutions incorporate a constant-index core (crucial for manufacturability). Simulations include a polychromatic and extended sun. A sample design for an f/1.40 solar lens is provided, where planar lenses comprise a concentrator module's protective glazing, with loss-less packing due to a square lens entry allowed by the modified truncated (non-full aperture) design, without incremental optical losses.

Spherical symmetric refractive index distributions also known as Gradient Index lenses such as the Maxwell-Fish-Eye (MFE), the Luneburg or the Eaton lenses have always played an important role in Optics. The recent development of the technique called Transformation Optics has renewed the interest in these gradient index lenses. For instance, Perfect Imaging within the Wave Optics framework has recently been proved using the MFE distribution. We review here the design problem of these lenses, classify them in two groups (Luneburg moveable-limits and fixed-limits type), and establish a new design techniques for each type of problem.

Designing optical systems for concentrating the flux of thermal neutrons and x-rays is severely constrained by the requirement of grazing incidence, i.e., the exceedingly small angles for total external reflection at mirror surfaces. As a result, the design principles established for non-imaging (i.e. flux concentrators) optics for visible light must be reconsidered. We present new concepts for improving the attainable flux density from neutron sources. In particular, we show how nested axisymmetric mirror systems including up to three reflections can achieve significantly higher concentrations.

We report the first direct measurement of the spatial coherence of solar beam radiation. Although often perceived as incoherent, direct sunlight exhibits spatial coherence at a sufficiently small scale. These dimensions were recently derived theoretically to be around two orders of magnitude greater than the wavelength. The partial coherence of sunlight raises tantalizing prospects for a new paradigm for solar power conversion via the antenna effect exploited so successfully in radio-frequency and microwave technologies (albeit at frequencies of order 1 PHz for solar). After reviewing the equal-time mutual coherence function of sunlight, we explain the particular suitability of a lateral cyclicshearing interferometer wherein the solar beam is split into two parts that are subsequently recombined with a relative lateral displacement. The method is relatively uncomplicated, inexpensive and obviates the problem of component dispersion (potentially problematic for a light source as broadband as sunlight). The experimental results are in good agreement with the recent theoretical predictions.

Thermal analysis of a high-power cw solar-pumped laser under development as a magnesium energy cycle driver has been conducted experimentally and analytically. The laser system is equipped with a Fresnel lens and a cone-shaped secondary mirror chamber (SMC). The SMC realizes a hybrid-pumping scheme combining axial- and side-pumping configurations to enhance solar light absorption to a rod-shaped laser medium. A non-uniform temperature profile was obtained during experiments due to combination of volumetric heating and surface cooling, which leads to a nonuniform variation of index of refraction in the laser medium. The thermal lensing and thermal stress-induced birefringence are analyzed.

Luminescent solar concentrators (LSCs) incorporating a dye doped thin film coating can be used as a wave-guide to absorb and redirect light to coupled solar cells. Coatings including dyes dispersed in a liquid crystalline host can be used to redirect absorbed light preferentially to the edges of a concentrator for collection by solar cells. The goal of this project is to demonstrate that a liquid crystalline host (UCL-‐018) can improve the gain of a solar concentrator, and to design an LSC based on this technology. To do this, various liquid crystal alignments are tested, as well as different designs that incorporate liquid crystalline thin films.

The current challenge for PV/Thermal (PV/T) systems is the reduction of radiation heat loss. Compared to solar thermal selective coating, the solar cells cannot be used as an efficient thermal absorber due to their large emissivity of the encapsulation material. Many commercial PV/T products therefore require a high concentration (more than 10x) to reach an acceptable thermal efficiency for their receivers. Such a concentration system inevitably has to track or semi-track, which induces additional cost and collects only the direct radiation from the sun. We propose a new PV/T design using a vacuum encapsulated thin film cell to solve this problem. The proposed design also collects the diffuse sun light efficiently by using an external compound parabolic concentrator (XCPC). Since the transparent electrode (TCO) of thin film cell is inherently transparent in visible light and reflective beyond infrared, this design uses this layer instead of the conventional solar cell encapsulation as the outmost heat loss surface. By integrating such a vacuum design with a tube shaped absorber, we reduce the complexity of conducting the heat energy and electricity out of the device. A low concentration standalone non-tracking solar collector is proposed in this paper. We also analyzed the thermosyphon system configuration using heat transfer and ray tracing models. The economics of such a receiver are presented.

We present observations on the linear programming algorithm proposed independently by Oliker and by Wang to design a single reflector for a point source and a far-field target. Given a set of source rays and discretized target intensities, the linear programming algorithm solves a variational problem to produce a reflector solution that consists of paraboloid patches. The computational complexity increases quadratically with the number of source rays and targets; this makes it important to minimize the number of source rays. However, minimizing the number of source rays results in solutions where the source rays at the intersection between neighboring patches split between multiple targets. This is unlike other discretized target reflector design methods, such as the Oliker supporting ellipsoid algorithm, that are used to aim numerous rays per ellipsoid at only one target. We uncovered a relationship between the optimal numbers of source rays and targets needed to run the problem. This relationship makes it possible to limit the number of source rays used in the design to the order of the number of target points. In this paper, we highlight the main features and current limitations of the linear programming algorithm. Finally, we propose a fast algorithm for 2D reflector design inspired by the intersection property of the linear programming method. The direct calculation method is shown to be several orders of magnitude faster than the linear programming method.

Starting with a seminal paper by Forbes [1], orthogonal polynomials have received considerable interest as descriptors of lens shapes for imaging optics. However, there is little information on the application of orthogonal polynomials in the field of non-imaging optics. Here, we consider fundamental cases related to LED primary and secondary optics. To make it most realistic, we avoid many of the simplifications of non-imaging theory and consider the full complexity of LED optics. In this framework, the benefits of orthogonal polynomial surface description for LED optics are evaluated in comparison to a surface description by widely used monomials.

The field of illumination optics has an increasing demand for free-form optics that produce arbitrary light distributions. In various applications an asymmetric, e.g. rectangular illumination can be beneficial, such as street lights, shop lights or architectural lighting. Yet there are only very few construction methods for free-form surfaces, especially using extended sources. One such method utilizes a manifold of conic sections to derive a source-target mapping for a particular source and target distribution. Although it relies on the assumption of a point source it can be adapted to work with real, extended sources. We implemented the algorithm to construct glass reflectors for almost arbitrary light distributions, either prescribed in the near- or far-field. Starting with a point source, an initial surface is optimized in a second process with a feedback loop to produce the desired result with the actual extended source. Our method is quite robust and was used to design for example an asymmetrical street light reflector. It was manufactured at Auer Lighting GmbH out of borosilicate glass. Measured target distributions are in excellent agreement with the simulations. These promising results show that this particular design method can be applied to real world applications. It is a powerful tool whenever a highly optimized reflector for a non-trivial illumination is required.

Based on the Monge-Kantorovich theory of optimal mass transport, the computation of a ray mapping between source and target irradiances is used to design two-sided freeform lenses fulfilling the constraints of an automotive application: compactness and sharp bright-dark cutoff. A generic segmentation technic resulting in Fresnel-type optics is presented and the whole procedure is illustrated with the design of a fog light lens. Finally Monte Carlo simulation of the virtual model and measurements of a polycarbonate prototype are presented.

Reverse ray tracing from a region of interest backward to the source has long been proposed as an efficient method of determining luminous flux. The idea is to trace rays only from where the final flux needs to be known back to the source, rather than tracing in the forward direction from the source outward to see where the light goes. Once the reverse ray reaches the source, the radiance the equivalent forward ray would have represented is determined and the resulting flux computed. Although reverse ray tracing is conceptually simple, the method critically depends upon an accurate source model in both the near and far field. An overly simplified source model, such as an ideal Lambertian surface substantially detracts from the accuracy and thus benefit of the method. This paper will introduce an improved method of reverse ray tracing that we call Reverse Radiance that avoids assumptions about the source properties. The new method uses measured data from a Source Imaging Goniometer (SIG) that simultaneously measures near and far field luminous data. Incorporating this data into a fast reverse ray tracing integration method yields fast, accurate data for a wide variety of illumination problems.

A multimode interference device is usually used in a variety of optical communication components, is a mature development of integrated optical components. Traditionally, the original of integrated optics usually be used in the field of optical communications, we will extend the applications of multimode interference device in this paper, we try multimode interference device applications in the field of natural light illumination systems and the lighting guides which our goal is each visible wavelength of light coupled with a waveguide transmission. In our proposed, we use poly(dimethylsiloxane)(PDMS) to fabricate this device, there is a high transmission efficiency(>95%) and over a very large bandwidth. The device demonstrated good confinement of visible light and low attenuation at 0.40 dB/cm.

Directly using sunlight for the illumination of rooms that have no windows is a very important measure for higher energy efficiency and CO₂ reduction in the next future, especially for countries along the sunny belt. The Sollektor ^®, developed at the Polymer Optical Fiber Application Center in Nuernberg, Germany, offers an efficient way to do that. The Sollektor is a combination of a plastic injection moulded concentrator optics array, a control unit which tracks the sun over the day and a polymer optical fiber bundle, guiding the collected light into the rooms. In order to ensure the illumination even at times without sun we present concepts and first results for the combination with conventional LED in order to obtain a 24 hillumination on a high efficiency level with high quality light.

A novel concept for an advanced fenestration system was studied and samples were produced to demonstrate the feasibility. The resulting novel glazing will combine the functions of daylighting, glare protection, and seasonal thermal control. Coated microstructures provide redirection of the incident solar radiation, thus simultaneously reducing glare and projecting daylight deep into the room in the same manner as an anidolic mirror-based system. The solar gains are reduced for chosen angles corresponding to aestival elevations of the sun, thereby minimizing heating loads in winter and cooling loads in summer. A ray-tracing program developed especially for the study of laminar structures was used for the optimization of structures with the above mentioned goals. The chosen solution is based on reflective surfaces embedded in a polymer film that can be combined with a standard doubled glazed window. The fabrication of such structures required several steps. The fabrication of a metallic mould with a relative high aspect ratio and mirror polished surfaces is followed by the production of an intermediate Polydimethylsiloxane moulds that was subsequently used to replicate the structure with a UV curable polymer. Selected facets of these samples were then coated with a thin film of highly reflective material in a physical vapour deposition process. Finally, the structures were filled with the same polymer to integrated the mirrors.

High dynamic range imaging has been shown to be a reliable tool to assess luminance maps and glare risk probability in buildings. However, there are some limitations of image capturing time, especially when dealing with highly dynamic and contrasted daylight situations. We used a newly developed prototype of a digital camera which contains a high dynamic range pixel array chip, with a logarithmic scale for encoding. This type of camera allows to effectively assessing luminance, contrast and contrast directions, by taking only a single image or by performing real time recordings. The device was equipped with a fisheye lens and V-lambda filters to adapt the camera’s spectral sensitivity to the human eye. After spectral as well as photometric calibration and vignetting correction, the device was tested to perform luminance mapping of real scenes. The results showed that luminance maps of a room can be efficiently assessed under dynamic daylight and mixed day- and electric lighting conditions in a very short time (i.e. 100 ms), when compared to classical HDR imaging techniques. This allows us to calculate glare indexes of a scene simultaneously. The camera opens a variety of new applications as a useful tool for architects, building designers and lighting experts. The device can be used to easily monitor daylight availability and glare indexes in existing buildings and further developments for advanced (day-) lighting control can be envisaged.

For some fiber optic applications, like high-end endoscopy, light sources with high luminance are necessary. Currently, short arc discharge lamps are being used. However, more and more LED solutions are trying to compete, but they can not yet reach the performance obtainable by 300 W Xenon short arc discharge lamps. To make this field of application accessible for solid state light sources, a new approach is necessary. Diode lasers have rapidly advanced in the past years. This is particularly true for multimode laser diodes emitting at around 445 nm wavelength. Single diodes emitting more than 1 W of optical power are already available. These laser sources exhibit extremely high radiance, thus they can be focused onto very small areas. Phosphors placed near the focus can result in high luminance sources. On the basis of this idea, a device has been developed to match the performance of a state of the art 300 W Xenon lamp system. An array of laser diodes is used to illuminate a phosphor plate which converts the blue pump light into yellow light. The converted light is collected and adapted to the application by a tapered TIR rod. To achieve a color point on the Planckian locus at 6000 K, the light of an LED emitting at around 460 nm is superimposed to the converted light.

Ray data sets describing light sources for illumination commonly contain starting points, directions and fl flux, and sometimes color. Simply adding luminance in addition to the flux which is already there, we gain useful design options not available otherwise. Adding luminance provides all information needed to apply the abstract, phase space based, concept of selecting maximum flux from given ètendue to real sources. Many light sources, e.g. arc lamps for projection, are used in rotationally symmetric optical systems. It is well known that the conservation of skewness imposes additional constraints on which parts of the source phase space can be transferred to the target. While it has been impractical in the past to apply this concept in practice, especially for sources with inhomogeneous luminance, we show how ray data sets including luminance can be readily used to determine fundamental upper limits on flux transfer efficiency in these cases, providing a valuable benchmark for actual optical designs.

In SSL general illumination, there is a clear trend to high flux packages with higher efficiency and higher CRI addressed with the use of multiple color chips and phosphors. However, such light sources require the optics provide color mixing, both in the near-field and far-field. This design problem is specially challenging for collimated luminaries, in which diffusers (which dramatically reduce the brightness) cannot be applied without enlarging the exit aperture too much. In this work we present first injection molded prototypes of a novel primary shell-shaped optics that have microlenses on both sides to provide Köhler integration. This shell is design so when it is placed on top of an inhomogeneous multichip Lambertian LED, creates a highly homogeneous virtual source (i.e, spatially and angularly mixed), also Lambertian, which is located in the same position with only small increment of the size (about 10-20%, so the average brightness is similar to the brightness of the source). This shell-mixer device is very versatile and permits now to use a lens or a reflector secondary optics to collimate the light as desired, without color separation effects. Experimental measurements have shown optical efficiency of the shell of 95%, and highly homogeneous angular intensity distribution of collimated beams, in good agreement with the ray-tracing simulations.

Optical design of a concentrating photovoltaic/thermal (CPVT) system is carried out. Using wavelength-selective optics, the system demonstrates 3-D concentration onto a solar cell and 2-D concentration onto a thermal receiver. Characteristics of the two types of concentrator systems are examined with ray-tracing analysis. The first system is a glazed mirror-based concentrator system mounted on a 2-axis pedestal tracker. The size of the secondary optical element is minimized to decrease the cost of the system, and it has a wavelength-selective function for performing 3-D concentration onto a solar cell and 2-D concentration onto a thermal receiver. The second system is a non-glazed beamdown concentrator system containing parabolic mirrors in the lower part. The beam-down selective mirror performs 3-D concentration onto a solar cell placed above the beam-down selective mirror, and 2-D concentration down to a thermal receiver placed at the bottom level. The system is mounted on a two-axis carousel tracker. A parametric study is performed for those systems with different geometrical 2-D/3-D concentration ratios. Wavelength-selective optics such as hot/cold mirrors and spectrum-splitting technologies are taken into account in the analysis. Results show reduced heat load on the solar cell and increased total system efficiency compared to a non-selective CPV system. Requirements for the wavelength-selective properties are elucidated. It is also shown that the hybrid concept with 2-D concentration onto a thermal receiver and 3-D concentration onto a solar cell has an advantageous geometry because of the high total system efficiency and compatibility with the piping arrangement of the thermal receiver.

In this research, we propose a high performance non-image illumination module of pico-projector which includes light source, collimator and liquid crystal on silicon (LCoS) panel. The light source is RGB LED. The collimator consists of two glass collimator lenses and two double sides micro lens array (MLA) for light homogenizer. MLAs play a critical role in the LED illumination module. Dual double-side MLAs have been adopted for the homogenizer to satisfy the numerical aperture in the optical design. The good uniformity and high accuracy MLA structure was generated by ultra precision diamond shaping method and the MLA plate is subsequently fabricated by injection molding. Finally, a non-image illumination module with power efficiency 30.87 lm/w and uniformity of 56% on LCoS panel in a very compact size, less than 1.6 cm3 in volume, has been developed.

In this paper, we investigated the optical characteristic of the light guide plate (LGP) with microstructures engraved by a CO₂ laser. The LGP is for edge-lit backlighting of liquid crystal display. Traditionally, the microstructures on largescaled LGP are formed by screen-printing, which are hardly formed by inject molding. However, the screen-printed LGP highly scatters light and has lower optical efficiency. Therefore, a method was proposed to use the laser to directly engrave the flat surface of a bare LGP with microstructures. The engraved LGP has better optical performance due to the polished surface of the engraved-microstructures, and can be used for large-scaled application such LCD TV backlighting. We used different processing parameters to engrave the microstructures of 11 different shapes on a bare LGP and measured the cross-sectional dimensions of the microstructure. Among them, five kinds of shapes were chosen to be engraved on the bare LGPs respectively as samples. The five LGP samples were measured for spatial and angular luminance by the BM7 and Conoscope. With difference in the profiles of the microstructures, the angular distributions of light emitting from the LGP also differ. All the experimental data of the samples were compared with one another and the on-axis luminance of the best LGP sample could potentially increase 50% more than the reference sample if a proper optical film was chosen to accompany it.