For the 4th time, the International Optical Design Conference (IODC) included an Illumination Design contest. This year, the contest involved designing the illuminator to produce a “100” logo to celebrate the OSA’s 100th anniversary. The goal of the problem was to produce the highest logo luminance with greater than 30% uniformity. There were 7 entries from 2 different countries. Two different commercial optical/illumination design packages were used. The winning solution, was provided by Steve Mulder.
In some applications, homogenization of a light beam in the spatial and angular dimensions is required. Known integrator schemes such as rod and fly’s eye integrators merely provide integration in one dimension, and do not work properly for strongly inhomogeneous beams. In this contribution, we investigate whether and how light mixing can be improved by a combination of two integrators with the help of an optical system.
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.
In the contribution we discuss the relationship between etendue and luminous flux of gobo projectors and its implications on illumination design and system architecture. On the basis of a given projector specification, a suitable LED type can be chosen and the number of needed LEDs and the necessary system etendue can be calculated. In a next step, we show how to design a suitable illumination system with primary and secondary optics and possibly including a homogenizer. Furthermore, implications for the design of the projection lens are discussed.
In our contribution, we discuss an optical system which is able to provide sun-like radiation on a CPV module. This system
is able to realize collimated light with more than 130 klx, with an angle of incidence of less than 0.26°. Special attention
is given to a uniform light distribution on an illuminated area of 8 × 8 inches. The resulting optical efficiency of
the system is 33%, much better than previously achieved with Xe flash lamp designs .
The design is based on a P-VIP 330/1.0 lamp, the latest in a series of OSRAM's P-VIP lamp types for video projectionwhich
is featuring a peak luminance of approximately 9 Gcd/m2. As a result of the enormous operating pressure of
the lamp, its spectrum is similar to the spectrum of the sun and will probably enable at least a class B simulator.
The device based on the described design delivers continuous, sun-like radiation. This way, features of CPV modules as
efficiency, angular sensitivity or tracking behavior can be tested during development or even in production.
A design concept for an extremely compact zoom optics which is suitable for illumination applications is presented.
Such optics is especially useful for camera or flash lights as the illuminated area can be adjusted according to the picture
content of the photo or film camera.
The principle of the design is as follows: Collimated light passes through two lenses, each with a freeform surface. The
freeform surfaces face each other and fit into one another perfectly. When the two lenses are merged together, they
basically represent a coplanar plate: The cone angle entering the merged lenses does not change while passing them.
When the plates are separated, the light is scattered at the freeform surfaces. Due to the smooth characteristics of the
freeform surfaces shape, the cone angle can be adjusted continuously with the distance of the zoom lenses.
The distance of the zoom lenses, which is necessary for maximum angle widening, is dependent on the size of the
structures of the freeform surfaces and can be reduced to the sub-millimeter range. The compactness of the resulting
device is a major advantage of the design concept.
The principle of operation of the design could be shown by the construction of a prototype. It features a LED light source
and a zoom range of 5° to 30° (cone angle). The luminous flux of the device is approx. 650 lm.
Discharge lamps serve a wide variety of applications and outperform novel light sources such as LEDs in terms of
luminous flux and luminance. Unfortunately, such lamps occasionally show arc movements (flicker) which change the
amount of light that is coupled into an optical system. A variety of measures in lamp design can suppress flicker
tendencies of a lamp but arc movement cannot be totally avoided.
In our contribution, we show that the way how the light is collected considerably influences the impact of flicker on the
collected luminous flux. We investigate light collection sensitivity of an illumination system as a function of the etendue
and of the particular realization of the illumination system. As a result, flicker sensitivity can be substantially reduced at
the expense of collection efficiency.
Elliptical reflectors are widely used to couple the radiation of a light source into an optical system. Such a system
usually collects the light with an integrating rod, a fiber, or any other kind of light guide. Its entrance window can be
conceived as an aperture and an acceptance angle.
In illumination designs with elliptical reflectors, sources and apertures are usually positioned in the focal points of the
ellipse, probably due to the fact that the foci form a stigmatic pair. This is then implicitly generalized to the case of
extended sources and apertures. Surprisingly, a careful investigation revealed that the maximum coupling efficiency is achieved if source and target are not positioned in the focal points. In this paper, a theoretical explanation of this effect is given by a calculation of
higher-order magnification properties of an elliptical reflector.
Finally, applications in current reflector designs for video projection lamps are shown.
We investigate a class of illumination systems, which consist of a light source, a conical (elliptical or parabolic) reflector and an optical device that collects the radiation. The collection efficiency of such systems is limited for conventional means of light collection such as rod and fly's eye integrators. The distribution of the collecting etendue in phase space differs from that of the light, which comes from the reflector. The mismatch is caused by a series of optical effects such as the actual shape of the source, a variable magnification of the conical section, and by consequences from skewness conservation.
Nevertheless, this situation is accepted as in many commercial devices, and one may at least ask what conditions yield best efficiency. We show, for example, how to calculate optimum eccentricity of an elliptical reflector to be used with a given source and integrator.
To go further and to reduce the etendue mismatch, one may either redesign the lamp for a better fit to the collection system or modify the collection method. Based on the analysis of the conical reflector, we discuss options to achieve better collection efficiency and show examples. For a simultaneous treatment of both elliptical and parabolic reflectors, we introduce a new method that describes the lamp by a luminance distribution on the director circle or plane of the conical section.
Elliptical reflectors are widely used in illumination engineering as a means to concentrate the light of a source in the secondary focal plane. To collect as much light from the source as possible, the reflector must cover a wide angular range of the emitted radiation, hence forward and backward reflections on the reflector must be discussed and conditions for paraxial optics do not apply. We develop a framework of relations that describe the image of an extended source in the secondary focal plane of the ellipsoid. After deriving basic relations between object and image spaces, the propagation of rays depending of their origin and on their direction is investigated. As a result, the function and the aberrations of the reflector can be expressed in terms of an angular dependent magnification for longitudinal and lateral coordinates. With that, one cannot not only calculate luminance and illuminance distributions in the secondary focal plane in a straightforward manner, but can easily understand their properties and their dependence on ellipse parameters. On the basis of the developed relations, implications for the design of "elliptical" short arc high-intensity-discharge (HID) lamps for video projection are discussed.
In our contribution we demonstrate a wide variety of ray tracing software applications for the design of VIP short-arc discharge video projection lamps. On the basis of simulations we derive design rules for the lamp itself and for its optical environment. Light Tools software acts as a means to understand the collection efficiency of a VIP lamp with an elliptical reflector and as an instrument to prove the conclusions.
We present a technique for the measurement of temporal phase differences. In this method, the holographic storage of a given wavefront in a photorefractive BaTiO3 crystal is combined with the interferometric phase-step technique. We obtain a novelty-filter phase-step method which allows for the measurement of phase changes within a unique process. The application and some features of the technique are demonstrated.
In our report we compare different ways of realizing an optical novelty filter with photorefractive barium titanate crystals. We present experiments on the basis of beam fanning, two-wave mixing and self-pumped phase conjugate geometries. The application of photorefractive novelty filters not only for phase visualization but also for the measurement of transient phase changes in a laser beam is demonstrated. The phase calculation from an interferogram is supplied or replaced by the novelty filter's phase transfer function. The use of such techniques instead of conventional interferometry for transient phase evaluation results in a simplified measuring procedure.
For the application of self-pumped phase-conjugate mirrors in interferometric arrangements, the properties of such devices have to be characterized. In this paper, we define figures of merit on the basis of experimental investigations and show, how the field of possible interferometric applications is limited in the case of a non-ideal phase conjugation process under stationary and transient conditions.
Our technique allows for the evaluation of a cross-section of a fringe pattern with a temporal resolution of 40 ms over a range of 20s. It can be applied to all two-beam interferometer, fringe projection, or ESPI techniques if a phase shift device is a part of the optical set-up.
We describe a real-time holographic interferometric set-up for the determination of dynamic deformations of reflecting surfaces. The optical storage medium used is based on the novel polymer poly(vinyl alcohol) with alkoxyazobenzencarbonyl substituent. This material does not need any development and is characterized by low costs.
Holographic enhancement in single crystal photorefractive fibers of Bi12Si020 (BSO) at 2i, = 514.5 nm and of Bii2Ti020 (BTO) at A, = 632.8 nm was measured as a function of spatial frequency and light polarization. Double phase conjugation of two mutually incoherent beams was observed in BTO-fiber under applied ac electric field.