Juan C. Miñano

Free-form integrator array optics

A new design method of free-form Kohler integrator array optics is presented. Only few solutions to the integrator design problem are known, which apply for specific and simple source and targets (for instance, flat integrator lenslet arrays when the source and target are squares located at infinity). The method presented here find more general solutions and the resulting optics is formed by two arrays of free-form optical surfaces (which can be either reflective of refractive). The contour curves of the array units are also obtained from the design. Two types of Kholer integrators will be defined, depending if they integrate only along one direction across the source (one-directional integrators) or in the two directions (two-directional integrators). This design method has been applied for an ultra-compact high efficiency LED low beam head lamp producing a legal pattern independently of the chip luminance variation and permitting LED position tolerances of ±200 microns. The ray tracing proves that the high gradient (0.32) and its vertical position in the pattern remain invariable when chip is moved.

Perfect imaging with geodesic waveguides

Transformation optics is used to prove that a spherical waveguide filled with an isotropic material with radial refractive index n=1/r has radially polarized modes (i.e. the electric field is only radial) with the same perfect focusing properties as the Maxwell fish-eye (MFE) lens. An approximate version of that device, comprising a thin waveguide with a homogeneous core, paves the way to experimentally attaining perfect imaging in the MFE lens.

Perfect drain for the Maxwell fish eye lens

Perfect imaging of electromagnetic waves using the Maxwell fish eye (MFE) requires a new concept: a point called the perfect drain that we shall call the perfect point drain. From the mathematical point of view, a perfect point drain is just like an ideal point source, except that it drains power from the electromagnetic field instead of generating it. We introduce here the perfect drain for the MFE as a dissipative region of non-zero size that completely drains the power from the point source. To accomplish this goal, the region must have a precise complex permittivity that depends on its size as well as on the frequency. The perfect point drain is obtained when the diameter of the perfect drain tends to zero. This interpretation of the perfect point drain is connected well with common concepts of electromagnetic theory, opening up both modeling in computer simulations and experimental verification of setups containing a perfect point drain.

TIR RXI collimator

A metal-less RXI collimator has been designed using the Simultaneous multiple surface method (SMS). Unlike conventional RXI collimators, whose back surface and parts of the front surface have to be metalized, this collimator is completely metal-free, made only of plastic (PMMA). The collimator’s back surface is designed as a grooved surface providing two TIR reflections for all rays impinging on it. One advantage of the design is the lower manufacturing cost, since there is no need for the expensive process of metalization. More importantly, unlike conventional RXI collimators, this design performs good colour mixing, as well as being very insensitive to the source non-uniformities. The experimental measurements of the first prototype show good agreement with the simulated design.

Free-form V-groove reflector design with the SMS method in three dimensions

The Simultaneous Multiple Surface design method in three dimensions (SMS3D) is applied to the design of free-form V-groove reflectors. The general design problem is how to achieve the coupling of two wavefronts after two reflections at the V-groove, no matter which side of the groove the rays hit first. This paper also explains a design procedure for thin dielectric grooved-reflector substitutes for conventional mirrored surfaces. Some canonical V-groove designs are ray-traced in detail.

Performance Modeling of Fresnel‐Based CPV Systems: Effects of Deformations under Real Operation Conditions

Getting a lower energy cost has always been a challenge for concentrated photovoltaic. The FK concentrator enhances the performance (efficiency, acceptance angle and manufacturing tolerances) of the conventional CPV system based on a Fresnel primary stage and a secondary lens, while keeping its simplicity and potentially low‐cost manufacturing. At the same time F‐XTP (Fresnel lens+reflective prism), at the first glance has better cost potential but significantly higher sensitivity to manufacturing errors. This work presents comparison of these two approaches applied to two main technologies of Fresnel lens production (PMMA and Silicone on Glass) and effect of standard deformations that occur under real operation conditions.

Ultra-High Efficiency, High-Concentration PV System Based On Spectral Division Between GaInP/GaInAs/Ge And BPC Silicon Cells

A novel HCPV nonimaging concentrator concept with high concentration (>500×) is presented. It uses the combination of a commercial concentration GaInP/GaInAs/Ge 3J cell and a concentration Back‐Point‐Contact (BPC) concentration silicon cell for efficient spectral utilization, and external confinement techniques for recovering the 3J cells 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 it, both POE and SOE performing Kohler integration to produce light homogenization. The band‐pass filter sends the IR photons in the 900–1200 nm band to the silicon cell. Computer simulations predict that four‐terminal terminal designs could achieve ∼46% added cell efficiencies using commercial 39% 3J and 26% Si cells. A first proof‐of concept receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ∼100× and lower simulated added efficiency), a...

Advanced PV concentrators

It is essential to obtain high values of tolerance for PV concentrators because manufacturing process always implies some accuracy errors. In this way, three new free-form concentrators are presented here, combining high geometric concentration and high tolerance (high acceptance angle). This is achieved by using the SMS3D design method, which is the most advanced method to design free-form surfaces in non-imaging optics. Uniform illuminance on the cell is important as well, for proper behavior and durability of the system, so our three designs will have homogenizer elements. We have added a homogenizer rod to one of the designs while for the other two Ko¿hler integrator configurations have been chosen. Concentration, acceptance angle and uniformity values obtained are shown in results section.

High performance Fresnel-based photovoltaic concentrator

It is essential to obtain high values of tolerance for CPV concentrators because manufacturing process always implies some accuracy errors. This paper presents the Fresnel Köhler concentrator (FK), an advanced optical concentrator comprising a Fresnel lens as a primary element and a refractive secondary element, both presenting free-form surfaces. This optic produces both, the desired light concentration and high tolerance (i.e. high acceptance angle), as well as an excellent light homogenization by Köhler integration simultaneously. A comparison between the FK and other current conventional Fresnel-based CPV concentrators is also presented, being our concentrator superior to its competitors in terms of tolerances, irradiance homogeneity and manufacturability.

Free form V-groove reflector design with the SMS method

The Simultaneous Multiple Surface design method (SMS) is applied to the design of free-form V-groove reflectors. The general design problem is to achieve perfect coupling of two wavefronts after two reflections at the groove, no matter which side of the groove the rays hit first. All possible 2D designs are listed and used as a basis for the 3D free-form reflector analysis. The extension to the 3D case is given, and illustrative particular canonical examples are developed. Besides the theory and design work, first prototypes were produced of a mirrorless TIR device using V-grooves that emulates a parabolic reflector. The experimental measurements of the TIR reflector show reflectance up to 98%.