This PDF file contains the front matter associated with SPIE Proceedings Volume 9572 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

In this paper we will discuss the one-dimensional Hottel string method as it applies to symmetric, infinite sources (as in the case of constructing ideal solar concentrators) and extend the theory to asymmetric, finite sources and demonstrate that an ideal concentrator can be created in this case. Furthermore, we will discuss the concept of flowlines and explore the yet unknown relationship between strings and flowlines.

The asymmetric compound elliptical concentrator (CEC) has been a less discussed subject in the nonimaging optics society. The conventional way of understanding an ideal concentrator is based on maximizing the concentration ratio based on a uniformed acceptance angle. Although such an angle does not exist in the case of CEC, the thermodynamic laws still hold and we can produce concentrators with the maximum concentration ratio allowed by them. Here we restate the problem and use the string method to solve this general problem. Built on the solution, we can discover groups of such ideal concentrators using geometric flux field, or flowline method.

We demonstrated an all fiber actively mode-locked laser emitting cylindrical vector beam. A few-mode fiber Bragg grating is adopted to achieve mode selecting and spectrum filtering. An offset splicing of single-mode fiber with fourmode fiber is utilized as a mode coupler in the laser cavity. A LiNbO3 Mach-Zehnder modulator is used to achieve active mode locking in the laser. The laser operates at 1547nm with 30 dB spectrum width of 0.3nm. The emitted modelocked pulses have a duration of 1ns and repetition of 12.06MHz. Both radially and azimuthally polarized beams have been obtained with very good modal symmetry by adjusting the polarization in the laser cavity.

In this contribution the line flow method is applied to an optimized secondary optics in a photovoltaic concentration system where the primary optics is already defined and characterized. This method is a particular application of photic field theory. This method uses the parameterization of a given primary optics, including actual tolerances of the manufacturing process. The design of the secondary optics is constrained by the selection of primary optics and maximizes the concentration at a previously specified collection area. The geometry of the secondary element is calculated by using a virtual source, which sends light in a first concentration step. This allows us to calculate the line flow for this specific case. This concept allows designing more compact and efficient secondary optics of photovoltaic systems.

A new dielectric totally internally reflecting concentrator (DTIRC) design has been developed for use with bifacial photovoltaic cells. The structure incorporates the bifacial cell standing vertically at the base of the structure, immersed in dielectric. DTIRC structures with single-sided photovoltaic receivers, like CPC structures, are designed using the paths of the edge rays to calculate the sidewalls. If these rays successfully hit the receiver then all rays at lower angles will also hit the receiver. In a vertical DTIRC structure, it is not just the edge rays that need to be taken into account in designing the structure. Around the bifacial receiver, rays at normal and close to normal incidence are the hardest to totally internally reflect onto the receiver. Once outside the area closest to the receiver, a modification of the maximum concentration method is used to design the remainder of the sidewalls. Ray tracing has been performed to confirm that the vertical DTIRC structure concentrates light as expected. The structure gives a lower concentration than a CPC with vertical bifacial receiver, however it is also a shorter structure with more uniform flux distribution over the receiver (leading to lower losses in the photovoltaic receiver).

The project team of University of California at Merced (UC-M), Gas Technology Institute, and Dr. Eli Yablonovitch of University of California at Berkeley developed a novel hybrid concentrated solar photovoltaic thermal (PV/T) collector using nonimaging optics and world record single-junction Gallium arsenide (GaAs) PV components integrated with particle laden gas as thermal transfer and storage media, to simultaneously generate electricity and high temperature dispatchable heat. The collector transforms a parabolic trough, commonly used in CSP plants, into an integrated spectrum-splitting device. This places a spectrum-sensitive topping element on a secondary reflector that is registered to the thermal collection loop. The secondary reflector transmits higher energy photons for PV topping while diverting the remaining lower energy photons to the thermal media, achieving temperatures of around 400°C even under partial utilization of the solar spectrum. The collector uses the spectral selectivity property of Gallium arsenide (GaAs) cells to maximize the exergy output of the system, resulting in an estimated exergy efficiency of 48%. The thermal media is composed of fine particles of high melting point material in an inert gas that increases heat transfer and effectively stores excess heat in hot particles for later on-demand use.

In this paper, a new type of linear focus, linear-tracking, catadioptric concentrator system is proposed and analysed for roof-integrated solar thermal applications. The optical concentrator designs have a focal distance of less than 10cm and are analysed using optical simulation software (Zemax). The results show that a relatively high concentration ratio (4.5 ~ 5.9 times) can be obtained and that the concentrators are capable of achieving an average optical efficiency around 66 - 69% during the middle 6 hours of a sunny day (i.e. a day with ~1000W/m² global irradiance). Optical efficiency is analysed for perfect and non-ideal optical components to predict the collector performance under different ‘practical’ circumstances. Overall, we intend for this paper to catalyse the development of rooftop solar thermal concentrators with compact form factors, similar to PV panels.

We present and analyze a design for a self-tracking solar concentrator based on a switchable-transparency optical element. The switchable element forms a moving aperture that tracks the motion of the sun to admit light into a CPC in which rays are 'recycled,' undergoing many passes through the concentrator to increase the absorption probability. This design has the benefit of not requiring any control of the angular profile of internal radiation, in contrast to other design that rely on total internal reflection to confine and transport the light. Via probabilistic models and rigorous ray tracing, we show that this design can exhibit performance comparable to other self-tracking designs. In particular we demonstrate a system with a 70x geometric concentration ratio and a tracking range of ±20°, achieving optical efficiencies of up to 65%.

Among the main challenges for systems based in solar concentrators and plastic optical fibers (POF) the accuracy needed for the solar tracking is founded. One approach to overcome these requirements is increasing acceptance angle of the components, usually by secondary optical elements (SOE), however this technique is effective for photovoltaic applications but it has not been analyzed for systems coupled to POFs for indoor illumination. On this subject, it is presented a numerical analysis of a solar collector assembled by a Fresnel lens as primary optical element (POE) combined with a compound elliptical concentrator (CEC) coupled to POF in order to compare its performance under incidence angle direction and also to show a trade-off analysis for two different Fresnel lens shapes, imaging and nonimaging, used in the collector system. The description of the Fresnel lenses and its designs are included, in addition to the focal areas with space and angular distribution profiles considering the optimal alignment with the source and maximum permissible incident angle for each case. For both systems the coupling between the optical components is analyzed and the total performance is calculated, having as result its comparison for indoor illumination. In both cases, the systems have better performance increasing the final output power, but the angular tolerance only was improved for the system with nonimaging concentrator that had an efficiency over 80% with acceptance angles 𝜃𝑖 ≤ 2° and, the system integrated by the imaging lens, presented an efficiency ratio over 75% for acceptance angles 𝜃𝑖 ≤ 0.7°.

We identify fundamentally new classes of aplanatic lenses where the focus resides inside the lens. These new aplanatic designs comprise a primary contoured dielectric entry, and a secondary contoured profile that, in general, is mirrored, but also admit solutions satisfying total internal reflection. We show that these aplanatic lenses engender 8 basic, distinct design categories, of which 6 yield physically admissible solutions. Flux concentration for far-field small-angle sources such as the sun and, conversely, narrow-field collimation of wide-angle emitting light sources such as LEDs can approach the thermodynamic limit. Losses due to chromatic aberration are smaller than in conventional lenses of comparable f-number, primarily due to the focus being in the lens. By the same token, exit numerical aperture can be increased by a factor of n (the dielectric's refractive index) - and hence flux concentration can be increased by a factor of n² - relative to common lenses where the focus resides outside the lens.

Today’s SSL illumination market shows a clear trend to high flux packages with higher efficiency and higher CRI, realized by means of multiple color chips and phosphors. Such light sources require the optics to provide both near- and far-field color mixing. This design problem is particularly challenging for collimated luminaries, since traditional diffusers cannot be employed without enlarging the exit aperture and reducing brightness. Furthermore, diffusers compromise the light output ratio (efficiency) of the lamps to which they are applied. A solution, based on Köhler integration, consisting of a spherical cap comprising spherical microlenses on both its interior and exterior sides was presented in 2012. The diameter of this so-called Shell-Mixer was 3 times that of the chip array footprint. A new version of the Shell-Mixer, based on the Edge Ray Principle and conservation of etendue, where neither the outer shape of the cap nor the surfaces of the lenses are constrained to spheres or 2D Cartesian ovals will be shown in this work. The new shell is freeform, only twice as large as the original chip-array and equals the original model in terms of color uniformity, brightness and efficiency.

Automatic optimization algorithms can be used when designing illumination systems. For systems with many design variables, optimization using an adjustable set of variables at different steps of the process can provide different local minima. We present a few examples of implementing a multi-step optimization method. We have found that this approach can sometimes lead to more efficient solutions. In this paper we illustrate the effectiveness of using a commercially available optimization algorithm with a slightly modified procedure.

Homogenize light is the principal purpose of mixing rods. Light extraction from mixing rods is proposed by changing the shape of the face, the rod or a combination of both for many applications. Light extraction also can be done by its lateral face by cutting the Mixing rod. In this work a simulation of square and hexagonal poly(methyl methacrylate) (PMMA) mixing rods were made in Radiant Zemax ® 12 release 2 designed with an elliptical transversal cut to extract light from a lateral face. The cut is specular for rays that fulfill the total internal reflection condition, the reflected rays are deviated and the Total Internal Reflection (TIR) condition broken, then, extracted. An advantage of this cut is that it can be controlled in depth to extract the amount of light required and the remaining light used for other purposes. Also it can reduce the size of the mixing rods and optical components. For the simulation, an LED light were used as source, the light were homogenized by the mixing rod and due to it, the light extracted is also homogenous. The polar power map, radiant intensity and color of the light extracted are presented and compared in both mixing rods.

There is currently a desire to produce thinner LED backlights and frontlights so that the devices which use these components can be as thin and lightweight as possible. This is particularly true for smartphones and tablets both of which make extensive use of such components. The push for thinner devices may lead to situations in which the backlights are thinner than the height of the LED emitting area. This paper deals with the coupling of LEDs and thin light guides, describing some possible ways to efficiently inject light from a relatively large LED into a thinner backlight. These solutions use étendue-squeezing optics, and linear edges which allow high-efficiency light injection.

The Simultaneous Multiple Surface (SMS) method was initially developed as a design method in Nonimaging Optics and later, the method was extended for designing Imaging Optics. We present the extension of the SMS method to design diffractive optical surfaces. This method involves the simultaneous calculation of N/2 diffractive surfaces, using the phase-shift properties of diffractive surfaces as an extra degree of freedom, such that N one-parameter wavefronts can be perfectly coupled. Moreover, the SMS method for diffractive surfaces is a direct method, i.e., it is not based in multi-parametric optimization techniques. Representative diffractive systems designed by the SMS method are presented.

We study the formation of wavefronts produced by smooth arbitrary surfaces with symmetry of revolution considering a plane wavefront propagating parallel to the optical axis and impinging on the refracting surface. The wavefronts are obtained by using the Malus-Dupin theorem and they represent the monochromatic aberrations which can be called image errors, furthermore their shapes could be modified by changing the parameters of the lens in such a way that if a caustic surface is vanished the optical system produces a perfect image, on the other hand for a caustic possessing a large area it could be applied to design non-imaging optical systems. The shape of the wavefront depends only on the indices of refraction and geometrical properties of the refracting surface such as the first derivative and their parameters associated. This analytic formula has potential applications in the microscopy field, illumination or corrector plates.

Axisymmetric aplanatic concentrators have been used in the past for solar concentrators and condensers (Gordon et. al, 2010). It is well know that such a system must be stigmatic and satisfy the Abbe sine condition. This problem is well known (Schwarzschild, 1905) to be solvable with two aspherics when the system has rotational symmetry. However, some of those axisymmetric solutions have intrinsically shading losses when using mirrors, which can be prevented if freeform optical surfaces are used (Benitez, 2007). In this paper, we explore the design of freeform surfaces to obtain full aplanatic systems. Here we prove that a rigorous solution to the general non-symmetric problem needs at least three free form surfaces, which are solutions of a system of partial differential equations (PDE). We also present the PDEs for a three surface full aplanat. The examples considered have one plane of symmetry, where a consistent 2D solution is used as boundary condition for the 3D problem. We have used the x-y polynomial representations for all the surfaces, and the iterative algorithm formulated for solving the above said PDE has shown very fast convergence.

We propose a new method to design freeform reflectors by nonuniformly sampling the source intensity distribution in double pole coordinate system. In double pole coordinate system, there is no pole for the whole hemisphere because both poles of the spherical coordinate system are moved to southernmost point of the sphere and overlapped together. With symmetric definition of both angular coordinates in the modified double pole coordinate system, a better match between the source intensity distribution and target irradiance distribution can be achieved for reflectors with large acceptance solid angle, leading to higher light efficiency and better uniformity on the target surface. With non-uniform sampling of the source intensity, we can design circular freeform reflector to obtain uniform rectangular illumination pattern. Aided by the feedback optimization, the freeform reflector can achieve the collection efficiency for ideal point source over 0.7 and relative standard deviation (RSD) less than 0.1.

Freeform optics is a relatively new field; it uses the methods necessary to describe surfaces lacking symmetry, and/or surfaces that create non-symmetrical irradiance distributions. The Supporting Quadrics Method (SQM) developed by Oliker is a superb for generating any desired irradiance distribution. The SQM uses an envelope of quadrics to create prescribed irradiance distributions. These optical systems are tested in ray trace software, where diffraction effects are not taken into account. It is important to understand the diffraction effects present in an optic, when moving from the ray trace stage to the prototype stage. Here we study the diffraction effects of Supporting Quadrics Method.

We present a cost-effective and large scale optical fiber daylighting system using non-imaging optics device such as array of linear Fresnel lenses and stepped-thickness waveguide as concentrator. The stepped-thickness waveguide is an optical component that can redirect focused sunlight from vertical to horizontal and guide light to the optical fiber. Our simulation results demonstrate an optical efficiency of up to 56.4% when the concentration ratio of the system is fixed at 100. The simulation also shows that this design has high tolerance for input angle of sunlight. The high tolerance allows replacing a dual axis sun tracking system with a single axis sun-tracking system as a cost-effective solution. Therefore, our results provide an important breakthrough for the commercialization of optical fiber daylighting systems that are faced with challenges related to high costs.