Secondary Optics Research Articles

Design of efficient LED optics with two free-form surfaces.

Most LED illumination applications require generation of complex light patterns for which the secondary optics with two free-form surfaces needs to be used. We present a novel optimization method for computing such type of optical elements. An analytical solution for the generation of the initial surfaces is proposed. To accelerate the optimization process, a specific surface representation is used, that eliminates the need to run a time-expensive raytracing procedure. As an example, an optical element generating uniformly illuminated rectangular area with size of 60° by 40° is computed. Lighting efficacy for the extended Lambertian source 1x1 mm is 88.5% and nonuniformity is less than 8.5%.

Function fitting the symmetric radiation pattern of a LED with attached secondary optic.

The analytical model [Moreno and Sun, Opt. Express 16, 1808-1819 (2008)] is applied to LED with attached secondary optics. It is shown that a slightly modified model using only three cosine power functions can be used for the cases with symmetric radiation pattern and that good fitting on realistic examples can be achieved with several standard optimization algorithms including local search heuristics and genetic algorithm.

On‐chip integration of laser‐ablated zone plates for detection enhancement of InGaAs bow‐tie terahertz detectors

One order of magnitude detection enhancement of bow-tie-shaped InGaAs-based terahertz detectors by on-chip incorporation of the secondary diffractive optics is reported. Zone plates were produced directly on the bottom surface of 500 µm-thick InP substrate using the direct laser write technique after an array of InGaAs detectors was formed on the front surface of the wafer. Measurements of detected signal dependence on the angle of the incident wave were performed at 0.76 THz and compared with finite-difference time-domain simulation results. Good correlation of the results shows that the observed enhancement is indeed caused by the focusing performance of the zone plate rather than by the exceptional sensitivity of the single detector.

Potential improvements in the optical and thermal efficiencies of parabolic trough concentrators

A detailed 3D heat transfer model is used to analyze the improvement potential of a typical parabolic trough concentrator (PTC) system with step-wise idealizations of system components. Sigmoid functions are used to idealize and optimize the optical behavior of the absorber tube selective coating. Reflectance, absorptance, and transmittance behavior is evaluated for the glass envelope, assessing the potential performance of a system with an ideal selective glass. Optical properties of the primary concentrator mirror, such as reflectivity as well as tracking and surface errors, are successively idealized to reveal the differences between ideal and real concentrators. In addition, the effect of the supporting structure is analyzed by reducing the number of heat collection elements (HCE) per mirror module, lowering the shaded area between HCEs, and removing the structure altogether. Applying these component idealizations individually yielded increases in thermal efficiency between 4.3% and 7.3% compared to a selected benchmark PTC design, while a combination of all idealizations resulted in an increase of 23%. The analysis of an alternative PTC design has shown that the idealization approach is robust in that it predicts similar increases in thermal efficiency. In a second step, several secondary mirror designs are evaluated and optimized, including a partially reflective glass surface, insulation in the vacuum annulus with reflective surfaces, as well as aplanatic mirror and tailored secondary designs. The analysis of systems with secondary optics revealed potential increases in thermal efficiencies between 0.8% and 1.6% compared to the benchmark design.

Outdoor test of a hybrid jet impingement/micro-channel cooling device for densely packed concentrated photovoltaic cells

Densely packed concentrated photovoltaic (CPV) receivers require efficient active cooling in order to maintain the photovoltaic cells within their nominal operating temperature range. The cooling device must have low thermal resistance coefficients and also provide good cell temperature uniformity in order to maximize the efficiency and the reliability of the whole system. A hybrid jet impingement/microchannel cooling device designed for CPV receivers is experimentally tested under real sun in outdoor conditions. The measurements include the irradiation profile at the outlet of the secondary optics and the temperature distribution of the receiver. The experimental results show that the thermal resistance coefficient and the temperature uniformity provided by the cooling device met the requirements for CPV receivers. This work also emphasizes that the internal geometry of the cooling device must be tailored, at the design stage, to the irradiation profile provided by the optics, which is generally nonperfectly uniform in CPV systems based on densely packed receivers. The impact of the solar concentration ratio and flow rate on the electrical output of the receiver is also assessed.

대면적 COB-type LED 패키지를 포함한 LED 램프의 좁은 광속각 구현을 위한 2차 광학계 최적 설계

In this paper secondary optics for an LED lamp with a narrow beam angle of 15° were optimized by using a two-reflector system, to reduce both its size and the occurrence of satellite rings. The conic constant and the curvature of the primary reflector were determined by considering the relation of the source size to the beam angle, and the optimal position and radius of the secondary reflector were found for reducing the occurrence of satellite rings. Luminous flux efficiency was about 80%.

A Novel Thin Concentrator Photovoltaic With Microsolar Cells Directly Attached to a Lens Array

We propose a novel concept of thin and compact CPV modules in which submillimeter solar cells are directly attached to lens arrays without secondary optics or an extra heat sink. With this small cell size, the optical path length of the module can be brought down to one-twentieth that of conventional CPV modules. To achieve precise alignment of the microsolar cells at the lens focal points, we have developed a fluidic self-assembly technique that utilizes surface tension. This novel CPV module with triple junction microsolar cells demonstrated an efficiency of 34.7% under sunlight in the particular measured condition.

Improving Beamtime Efficiency for Residual Stress Neutron Experiments

Starting during the shut-down of the HZB research reactor BER-II in 2011/2012 the E3 residual stress and texture diffractometer in Berlin underwent a comprehensive upgrade. The investments were broken down into different criteria, such as enhancing the instrument performance and accuracy as well as extending the range of applications for the user community. Here, we report about the gains achieved after integrating and commissioning the individual hardware and software tools included in the upgrade project, namely a motorized primary slit to accurately adjust the gauge volume, a secondary optics radial collimator and a laser scanner to precisely and quickly align the sample. The integration of the presented devices is further supported by software developments to shorten the instrument alignment procedure and measurement time. The upgrade has improved the efficiency of the available neutron beamtime.

Investigation of solar simulator based on high-power light-emitting diodes

High-power light-emitting diodes for application in a solar simulator were evaluated. The solar simulator was designed using only 6 types of high-power LEDs. The irradiance non-uniformity of this simulator was investigated and it was demonstrated that a small array (only 25 units) of selected light-emitting diodes can provide sufficient irradiance to achieve AM1.5G requirements for the test area of at least several cm in diameter without any secondary optics.

Performance Analysis of a 3.5 kWp CPV System with Two-axis Tracker

This paper presents the preliminary operational results of two 3.5 kWp CPV systems using triple junction III-V solar cells and a two-axis tracking mechanism. The plant is installed in the campus of the Università Politecnica delle Marche (Ancona, Central Italy). The concentration optics consists of a primary Fresnel lens and a secondary reflective optics with an overall geometrical concentration ratio of 476 X. An experimental measurement setup acquires the main plant operating and ambient quantities; the paper reports the first months of plant operation with particular focus on the influence of the available radiation and the ambient temperature on the performance of the system. The electric output has a linear trend with the available direct normal radiation while ambient temperature has a minor effect on the performance of the CPV systems; also the influence of the Air Mass coefficient is reported.

Design of A 16-Cell Densely-packed Receiver for High Concentrating Photovoltaic Applications

A novel densely packed receiver for concentrating photovoltaics has been designed to fit a 125× primary and a 4× secondary reflective optics. It can allocate 161cm2-sized high concentrating solar cells and is expected to work at about 300 Wp, with a short-circuit current of 6.6 A and an open circuit voltage of 50.72V. In the light of a preliminary thermal simulation, an aluminum-based insulated metal substrate has been use as baseplate. The original outline of the conductive copper layer has been developed to minimize the Joule losses, by reducing the number of interconnections between the cells in series. Slightly oversized Schottky diodes have been applied for bypassing purposes and the whole design fits the IPC-2221 requirements. A full- scale thermal simulation has been implemented to prove the reliability of an insulated metal substrate in CPV application, even if compared to the widely-used direct bonded copper board. The Joule heating phenomenon has been analytically calculated first, to understand the effect on the electrical power output, and then simulate, to predict the consequences on the thermal management of the board. The outcomes of the present research will be used to optimize the design of a novel actively cooled 144-cell receiver for high concentrating photovoltaic applications.

Method for computation of led secondary optics for automotive headlight

We propose a new analytical method for the calculation of an optical element that forms the intensity distribution in compliance with the requirements for automotive-beam headlamps. The optical element consists of a collimator, operating on the principle of total internal reflection (TIR), and a microlens array, creating the required intensity distribution. As an example, an optical element producing the headlight beam of classes B, C, D is presented. With an optical element of size 33 × 23 mm, it is enough to use two modules to generate a headlight beam of classes B, C and three modules for a headlight beam of class D.

Experimental and Numerical Study of a Parabolic Trough Linear CPVT System

The electric and thermal performance of a parabolic trough linear concentrating photovoltaic-thermal (CPVT) system operating in Padova (northern Italy) is experimentally investigated. The system moves about two axes and exhibits a geometrical concentration ratio around 130. The receiving module placed on the focus line displays a secondary optics made of two flat mirrors to gather some reflected radiation and to contribute to the concentrated flux on two lines of triple junction photovoltaic cells soldered on a ceramic substrate. The substrate is in thermal contact with a aluminium heat exchanger with water flow channels to cool the PV cells.During the test runs, the inlet water temperature ranges from 20°C to 80°C and the heat yield is obtained from mass flow rate and temperature measurements while a rheostat and a power analyzer are connected to the electric terminals of the module to assess the electrical production. The direct normal irradiation (DNI) is measured by a pyrherliometer mounted on a solar tracker. Experimental results are used to assess a numerical model of the solar receiver and the whole concentrator.

Surpassing the 2D Limit: A 600x High-concentration PV Collector Based on a Parabolic trough with Tracking Secondary Optics

We report on the design and performance of a novel 600x high-concentration photovoltaic (HCPV) collector. The design is unique in that it diverges from the predominant HCPV approach of a 3D concentrator mounted on a 2-axis tracker. We consider minimization of the cost per m2 of collecting aperture to be the most important aspect in achieving cost-competitiveness. Accordingly, we borrow from the knowledge of the more mature CSP industry which has shown the parabolic trough to be an effective and economical method to concentrate sunlight. To further leverage the advantages of scalability of trough geometries, the primary concentrator utilizes a construction based on inflated metalized polymer membranes as reflectors supported on modular concrete structures. With this design, aperture widths surpassing 10 m and trough lengths exceeding 200 m are possible. At a trough length of 200 m, the rated power of one collector is 500 kWp. To augment the concentration into the realm of HCPV, where use of high-efficiency triple-junction concentrator cells becomes economically viable, a novel secondary concentrating stage is employed, consisting of an array of tracking non-imaging concentrators arranged along the focal line of the primary. This two-stage line-to-point focus system allows for concentrations of over 600x, considerably surpassing the 2D limit of ∼200x inherent to trough-like geometries, while maintaining the advantages of a one-axis tracking trough primary concentrator. A full-scale prototype of the system has been constructed in Biasca, Switzerland. Year-round solar-to-electrical efficiency is expected to exceed 25%.

Optical Damage Tests on Reflecting Materials for Solar Applications Using Concentrated Sunlight

Concentrated Solar Power (CSP) and Concentrating Photovoltaics (CPV) usually involve secondary optics (lenses or mirrors) in order to improve system energetic performances. These secondary elements should collect the sunlight concentrated by the primary optic. Therefore, the materials suitable for the realization of secondary concentrators must withstand a long-time exposure to solar high power densities without significant decay of their optical performances. An accurate optical characterization of these materials should include an investigation on their degree of resistance to high-power light, by means of exposing them to concentrated sunlight for several hours in monitored conditions.This paper presents the optical study on three samples of two different materials, which are possible candidate for the construction of secondary reflectors for a solar furnace. The goals of this study were to test the samples endurance at the working power density, verifying if an achievable damage threshold exists and eventually correlating it with some measurable parameters like exposure time or temperature. In synthesis the tests were of two types: field tests with sun exposure and laboratory optical characterization.The field test consisted in exposing the samples (named A, B and C) to sunlight by using a dual-axis solar tracker and a suitable Fresnel lens. Samples A and B were sections of the same glass mirror. Sample C was a multilayer mirror based on an aluminum substrate. The measured parameters were: temperature of the back side of the sample; solar power density concentrated on the sample; exposure time.The optical characterization involved measurements of reflectance, regularly performed to check variations in the optical features. Only sample B suffered a structural failure at the end of the exposure period, and this involved only the glass cover; none of the samples showed appreciable decays in reflectance during the whole exposure period.

Theory and design of line-to-point focus solar concentrators with tracking secondary optics

The two-stage line-to-point focus solar concentrator with tracking secondary optics is introduced. Its design aims to reduce the cost per m(2) of collecting aperture by maintaining a one-axis tracking trough as the primary concentrator, while allowing the thermodynamic limit of concentration in 2D of 215× to be significantly surpassed by the implementation of a tracking secondary stage. The limits of overall geometric concentration are found to exceed 4000× when hollow secondary concentrators are used, and 6000× when the receiver is immersed in a dielectric material of refractive index n=1.5. Three exemplary collectors, with geometric concentrations in the range of 500-1500× are explored and their geometric performance is ascertained by Monte Carlo ray-tracing. The proposed solar concentrator design is well-suited for large-scale applications with discrete, flat receivers requiring concentration ratios in the range 500-2000×.

Light Distribution Design on Different LED Lamp

LED has characters of small size, long life and low power consumption, and it is environmental friendly. These advantages make LED have a huge market in the lighting industry. LED with the light distribution design can meet the requirements of the application under different circumstances. With the acknowledgement of the principles of light distribution design, based on optical engineering software LightTools, we study the light distribution design of LED back light module for direct-down illumination and LED shadowless lamp. After the secondary optics light distribution design of the LED light, its transmittance and uniformity has been noticeably improved. We depict different types of micro-structure on the surface of 3mm thickness PMMA diffuser, test and analysis the optical properties of the diffuser under different microstructure.

Optical analysis of deviations in a concentrating photovoltaics central receiver system with a flux homogenizer

The application of a kaleidoscope as a flux homogenizer to a concentrating photovoltaics system with a central receiver is investigated. The optical setup of a primary dish-type concentrator, a secondary homogenizer optics, and a photovoltaic receiver is simulated using ray tracing. The influence of various deviations from the ideal-namely sunshape (circumsolar radiation), shading, tracking error, and shape of the primary optical concentrator-on the performance of the homogenizer is analyzed quantitatively using the optical efficiency and the normalized standard deviation as a measure of inhomogeneity. Flux distributions for different progressively increasing deviations are discussed qualitatively. Experimental validation of the simulation is presented. It is demonstrated that the performance of the homogenizer is not particularly sensitive to sunshape. If sufficient length is provided, the homogenizer effectively compensates for tracking error, misalignment, and shape deviations of the primary concentrator. Yet despite the presence of the homogenizer, shading due to the holder of the receiver significantly affects the flux distribution at the receiver.

Using Bezier curves in the automatic design of nonimaging optical systems

This letter shows how to use Bezier curves in the design of nonimaging reflectors and lenses. The curve is simplified to increase the ray-tracing rate. A program library is created that describes objects on the basis of Bezier curves, using the zemax system. A technique for optimizing and calculating the secondary optics of LEDs is considered.

WIDE-FIELD ASTRONOMICAL MULTISCALE CAMERAS

In order to produce sufficiently low aberrations with a large aperture, telescopes have a limited field of view. Because of this narrow field, large areas of the sky at a given time are unobserved. We propose several telescopes based on monocentric reflective, catadioptric, and refractive objectives that may be scaled to wide fields of view and achieve 11 resolution, which in most locations is the practical seeing limit of the atmosphere. The reflective and Schmidt catadioptric objectives have relatively simple configurations and enable large fields to be captured at the expense of the obscuration of the mirror by secondary optics, a defect that may be managed by image plane design. The refractive telescope design does not have an obscuration but the objective has substantial bulk. The refractive design is a 38 gigapixel camera which consists of a single monocentric objective and 4272 microcameras. Monocentric multiscale telescopes, with their wide fields of view, may observe phenomena that might otherwise be unnoticed, such as supernovae, glint from orbital space debris, and near-earth objects.