This PDF file contains the front matter associated with SPIE Proceedings Volume 9629, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.
Many commercial, medical and scientific applications of the laser have been developed since its invention. Materials processing applications, like cutting or welding; and medical applications, like corneal surgery are just a few examples that may require a specific beam irradiance distribution to ensure optimal performance. Often, it is possible to apply geometrical optics to shape a laser beam. This common design approach has been thoroughly studied in the past and is based on the ray mapping between the input and output beam. Even though analytic expressions for various ray mapping functions exist, the surfaces of the lenses are still calculated numerically. In this work, we present an alternative approach that is based on the analytic description of the optical design problem by means of functional differential equations. A basic beam expander setup is used to explain how the equations are derived from Fermat's principle and solved using a Taylor series Ansatz. To demonstrate the versatility of this new approach, a further example of a Gaussian to at-top irradiance distribution beam shaping system is solved. So far discussed beam shaping systems are only capable of creating a static intensity distribution. Dynamic beam shaping systems can achieve time-varying distributions; an important functionality for some applications. For example, zoom beam expanders offer variable magnification levels by translating the axial positions of the lenses. It will be shown that this analytic design method is capable of solving such dynamic optical systems. All presented ray tracing results demonstrate a high calculation accuracy and underline the potential of this design approach for refractive beam shaping applications.
Portable runway lighting systems pose an interesting illumination challenge. They are typically used in harsh environments where generators or batteries are used to provide electricity. As a result, not only do the systems have to satisfy the regulatory requirements which determine the light intensity profile but they also need to be highly efficient and within a compact design. This paper summarises the optical design and performance of a PAPI system using LEDs which are coupled into a waveguide to generate the required light distribution at an intermediate plane after the waveguide. The use of waveguides means that a single projection lens is used to generate the final beam and this images the output of the waveguides into the far field.
Common illumination systems in short wave infrared (SWIR) hyperspectral imaging (HSI) include direct or
indirect tungsten halogen lights. While direct lights provide more radiation onto the samples than dome setups,
thus being more energy efficient, the acquired images often suffer from specular reflections and gloss. Glare
artifacts in images increase variability in the data limiting the accuracy of machine vision algorithms for defect
detection and quality inspection, or even providing false positives. Although domes are known to provide a
near Lambertian illumination and glare free images, glossy regions and heterogeneities may remain in the data
in practice. More particularly, in the field of fruit and vegetable quality inspection, due to their waxy surface,
it remains challenging to design an efficient realistic lighting system. This paper suggests a new approach
to optimize the illumination of fruit and vegetables based on measurements of the bidirectional reflectance
distribution function (BRDF), shape and Stokes parameters. From these measured values, a BRDF model is
loaded into ray-tracing software for realistic illumination engineering in order to determine the most suitable
illumination scheme. This concept is applied to apples and a cross polarizer (CP) with freeform optics (FO)
optical configuration is proposed, which allows the FO to be optimized to maximize uniformity in the field
of view of the imager and removes the parallel polarized gloss on the apples. The performance of this CP
illumination system was determined experimentally for a set of apples. This cross polarized (CP) illumination
system provided a uniformity (U) of 92% and an efficiency (ν) of 90%, while U = 87% and ν = 14% for an
ideal dome configuration when illuminating a rectangular target. The simulated imaged apples with assigned
optical properties performed better with CP (U=80%) than when using a dome (U=73%) by 7%. Finally, the
sensitivity of the design for the light positioning and spectral tolerance are investigated.
Today’s SSL illumination market shows a clear trend towards 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 (so increasing étendue).
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. When placed on top of an inhomogeneous multichip Lambertian LED,
this so-called Shell-Mixer creates a homogeneous (both spatially and angularly) virtual source, also Lambertian, where
the images of the chips merge. The virtual source is located at the same position with essentially the same size of the
original source. The diameter of this optics was 3 times that of the chip-array footprint.
In this work, we present a new version of the Shell-Mixer, based on the Edge Ray Principle, where neither the overall
shape of the cap nor the surfaces of the lenses are constrained to spheres or rotational Cartesian ovals. This new Shell-
Mixer is freeform, only twice as large as the original chip-array and equals the original model in terms of brightness,
color uniformity and efficiency.
TIR collimator are essential illumination components demanding high efficiency, accuracy, and uniformity. Various illumination
design methods have been developed for different design domains, including tailoring method, design via optimization,
mapping and feedback method, and the simultaneous multiple surface (SMS) method. This paper summarizes
and compares the performance of these methods along with the advantages and the limitations.
We present a detailed investigation of an optical system which couples the light of a Lambertian Source (for example, a high power LED array) to an equal etendue target. Such a system can be applied for gobo illumination or for illuminating a lightguide. Though the efficiency of such a system may by ideal in theory, real-world constraints make it imperfect. The actual light collection angle by the target may play a role, and requirements such as the clearance between the optics and source or target and the maximum system diameter will have an influence on imaging and non-imaging designs. As for some applications an uniform illumination of the target may be required, we finally analyze the ability of various designs to deliver homogeneity.
The problem of focusing light flux into an arbitrary curve in 3D space arises in the design of different laser or illumination systems. Using a diaphragm with a curved hole is not efficient and does not work for any 3D pattern. In this study, we propose a numerical analytical approach for designing reflective surfaces that efficiently produces the prescribed intensity distribution on the arbitrary curve in 3D space. The method consists of two steps: computation of the eikonal function on the curve and reconstruction of the reflective surface using the precomputed eikonal function. In the first step, we use the iterative technique for obtaining the eikonal function in the set of points on the curve. After that, we compute the continuous eikonal function by interpolation of the obtained values of the eikonal in points and reconstruct the reflective surface using continuous eikonal distribution. As examples, the reflectors generating spiral lines on the inclined plane and illumination system module are computed and simulated. Simulation data show the high quality of the produced illuminance distributions.
The concept of multichannel array projection is generalized in order to realize an ultraslim, highly efficient optical system for structured illumination with high lumen output, where additionally the Köhler illumination principle is utilized and source light homogenization occurs. The optical system consists of a multitude of neighboring optical channels. In each channel two optical freeforms generate a real or a virtual spatial light pattern and furthermore, the ray directions are modified to enable Köhler illumination of a subsequent projection lens. The internal light pattern may be additionally influenced by absorbing apertures or slides. The projection lens transfers the resulting light pattern to a target, where the total target distribution is produced by superposition of all individual channel output pattern. The optical system without absorbing apertures can be regarded as a generalization of a fly’s eye condenser for structured illumination. In this case light pattern is exclusively generated by freeform light redistribution. The commonly occurring blurring effect for freeform beamshaping is reduced due to the creation of a virtual object light structure by means of the two freeform surfaces and its imaging towards the target. But, the remaining blurring inhibits very high spatial frequencies at the target. In order to create target features with very high spatial resolution the absorbing apertures can be utilized. In this case the freeform beamshaping can be used for an enhanced light transmission through the absorbing apertures. The freeform surfaces are designed by a generalized approach of Cartesian oval representation.
Axisymmetric aplanatic systems 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.
Using conventional mapping algorithms for the construction of illumination freeform optics’ arbitrary target pattern can be obtained for idealized sources, e.g. collimated light or point sources. Each freeform surface element generates an image point at the target and the light intensity of an image point is corresponding to the area of the freeform surface element who generates the image point.
For sources with a pronounced extension and ray divergence, e.g. an LED with a small source-freeform-distance, the image points are blurred and the blurred patterns might be different between different points. Besides, due to Fresnel losses and vignetting, the relationship between light intensity of image points and area of freeform surface elements becomes complicated. These individual light distributions of each freeform element are taken into account in a mapping algorithm. To this end the method of steepest decent procedures are used to adapt the mapping goal. A structured target pattern for a optics system with an ideal source is computed applying corresponding linear optimization matrices. Special weighting factor and smoothing factor are included in the procedures to achieve certain edge conditions and to ensure the manufacturability of the freefrom surface. The corresponding linear optimization matrices, which are the lighting distribution patterns of each of the freeform surface elements, are gained by conventional raytracing with a realistic source. Nontrivial source geometries, like LED-irregularities due to bonding or source fine structures, and a complex ray divergence behavior can be easily considered. Additionally, Fresnel losses, vignetting and even stray light are taken into account. After optimization iterations, with a realistic source, the initial mapping goal can be achieved by the optics system providing a structured target pattern with an ideal source.
The algorithm is applied to several design examples. A few simple tasks are presented to discussed the ability and limitation of the this mothed. It is also presented that a homogeneous LED-illumination system design, in where, with a strongly tilted incident direction, a homogeneous distribution is achieved with a rather compact optics system and short working distance applying a relatively large LED source. It is shown that the lighting distribution patterns from the freeform surface elements can be significantly different from the others. The generation of a structured target pattern, applying weighting factor and smoothing factor, are discussed. Finally, freeform designs for much more complex sources like clusters of LED-sources are presented.
Modern Automotive headlamps enable improved functionality for more driving comfort and safety. Matrix or Pixel light
headlamps are not restricted to either pure low beam functionality or pure high beam. Light in direction of oncoming
traffic is selectively switched of, potential hazard can be marked via an isolated beam and the illumination on the road
can even follow a bend. The optical architectures that enable these advanced functionalities are diverse.
Electromechanical shutters and lens units moved by electric motors were the first ways to realize these systems.
Switching multiple LED light sources is a more elegant and mechanically robust solution. While many basic
functionalities can already be realized with a limited number of LEDs, an increasing number of pixels will lead to more
driving comfort and better visibility. The required optical system needs not only to generate a desired beam distribution
with a high angular dynamic, but also needs to guarantee minimal stray light and cross talk between the different pixels.
The direct projection of the LED array via a lens is a simple but not very efficient optical system. We discuss different
optical elements for pre-collimating the light with minimal cross talk and improved contrast between neighboring pixels.
Depending on the selected optical system, we derive the basic light source requirements: luminance, surface area,
contrast, flux and color homogeneity.
New analytical method for the calculation of the LED secondary optics for automotive high-beam lamps is presented. Automotive headlamps should illuminate the road and the curb at the distance of 100-150 meters and create a bright, flat, relatively powerful light beam. To generate intensity distribution of this kind we propose to use TIR optical element (collimator working on the total internal reflection principle) with array of microlenses (optical corrector) on the upper surface. TIR part of the optical element enables reflection of the side rays to the front direction and provides a collimated beam which incidents on the microrelief. Microrelief, in its turn, dissipates the light flux in horizontal direction to meet the requirements of the Regulations 112, 113 and to provide well-illuminated area across the road in the far field. As an example, we computed and simulated the optical element with the diameter of 33 millimeters and the height of 22 millimeters. Simulation data shows that three illuminating modules including Cree XP-G2 LED and lens allow generating an appropriate intensity distribution for the class D of UNECE Regulations.
The most common method to create white light with LEDs is the use of a luminescent material (e.g. phosphor) in combination with one or more blue LEDs. Different configurations can be used (intimate phosphor, remote phosphor, phosphor layer on top of a chip-on-board LED array). To design high quality LED sources it is important that these systems can be optimized. The Monte Carlo ray-tracing method is the traditional algorithm to simulate these systems. A disadvantage of the Monte Carlo method however is the large computation time which makes it less suitable for system optimization.
We present a new simulation method to predict the performance of various white LED packages with a planar phosphor layer using the extended Adding-Doubling method. In a phosphor converted white LED part of the incident and converted light is back-scattered from the phosphor layer towards the LED package. This light will be partly reflected back onto the phosphor layer by the LED package. When simulating the LED source with the extended Adding-Doubling method, the behavior of the LED package can be approximated by a reflection matrix. This matrix includes the directions in which the light is scattered from the LED package, as well as the efficiencies.
We found that, by using the extended Adding-Doubling method with the appropriate reflection matrix, it is possible to predict the total flux and the spectral angular intensity distribution of the light emitted from white LED packages with a planar luminescent layer. With this method we present a fast technique to predict the performance of phosphor converted white LEDs and optimize the optical parameters of the luminescent layer to obtain the best overall performance.
Link between roughness and Bidirectional Scatter Distribution Function (BSDF) is a challenging issue but a necessary step for designers. Indeed optical designers often speak about scattering where manufacturers speak about roughness. This link would enable an easier understanding between both parts, ending up with better designs. Besides, optical design software deal very well with BSDF, but ray tracing time can be strongly impacted when you have a lot of them in your design. Therefore, replacing BSDF by a real geometrical shape such as the roughness could be of a big benefit.
How can we link BSDF to roughness? We worked on two ways of finding a link between BSDF and roughness. From measured BSDF with Reflet Bench, we tried to find the equivalent roughness using He-Torrance model. Still using He-Torrance model we also tried to compute the BSDF knowing a roughness profile from a sample. The study showed great results with specular samples. When roughness is at least ten times bigger than the wavelength, roughness could be estimated within 5% precision. Above this limit, roughness can still be computed but with a 50% precision, which gives us at least an order of magnitude estimation. We also found with our method that, the more scattering the sample is, the more difficult it is to estimate roughness.
Thanks to such a link between roughness and BSDF, it becomes much easier to understand how to go from one to the other. This can be very useful for optical designers, but also for manufacturer who wants to perform roughness measurement. Designers who need a certain scattering for their optical designs, can therefore easily speak with manufacturers by giving them a roughness value to perform the BSDF they are looking for.
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 show an extension of the SMS method to diffractive surfaces. Using this method, diffractive kinoform surfaces are calculated simultaneously and through a direct method, i. e. it is not based in multi-parametric optimization techniques. Using the phase-shift properties of diffractive surfaces as an extra degree of freedom, only N/2 surfaces are needed to perfectly couple N one parameter wavefronts. Wavefronts of different wavelengths can also be coupled, hence chromatic aberration can be corrected in SMS-based systems. This method can be used by combining and calculating simultaneously both reflective, refractive and diffractive surfaces, through direct calculation of phase and refractive/reflective profiles. Representative diffractive systems designed by the SMS method are presented.
We collect the scorpions, Isometrus maculates, in different instars to analyze the
photoluminescence (PL), micro‐structure of cuticles and their correlation. The photoluminescence is
excited by 405 nm solid laser in room temperature and detected by BWtek BRC 112E spectrometer. The
result shows that the intensity of photoluminescence positively correlate to instars of scorpion. The
images of micro‐structures of cuticles captured by scanning electron microscope (SEM) present the
multilayer structure in detail. The samples are prepared in small piece to ensure that the PL and SEM
data are caught from the same area. The correlation between instars and intensity of
photoluminescence is explained according to micro‐structures via the thin‐film optics theory.
OLED can be applied as highly efficient and high-resolution patternable illumination source for controllable and steerable backlights, e.g., for use in autostereoscopic displays. To evaluate technology and approach a 3.5” 3D QVGA display prototype has been developed and combines several achievements: large-area OLED backlight, highly-efficient and fast-response OLED top-emitter, striped patterned backlight, individual electronic driving for adaptive backlight control and 3D mobile display application.