Florian Fournier

Fast freeform reflector generation using source-target maps

We propose a freeform reflector design method based on the mapping of equi-flux grids between a point source and a target. This method imposes no restriction on the target distribution, the reflector collection angle or the source intensity pattern. Source-target maps are generated from a small number of target points using the Oliker algorithm. Such maps satisfy the surface integrability condition and can thus be used to quickly generate reflectors that produce continuous illuminance distributions.

Optimization of freeform lightpipes for light-emitting-diode projectors.

Standard nonimaging components used to collect and integrate light in light-emitting-diode-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of transmission efficiency and spatial uniformity. We show that the simultaneous optimization of the output surface and the profile shape yields transmission efficiency within the étendue limit up to 90% and spatial uniformity higher than 95%, even for compact sizes. The optimization process involves a manual study of the trends for different shapes and the use of an optimization algorithm to further improve the performance of the freeform lightpipe.

Design Methodology for High Brightness Projectors

The low luminance levels of light-emitting diodes (LEDs) compared to arc lamps make it difficult to design high-brightness LED-based projectors. Besides, the specificities of LEDs do not always allow using the same design schemes as with arc lamp-based projection displays. This paper performs a taxonomy of the techniques that can be used to increase the brightness of LED-based projection displays. We show that, in etendue-limited systems, the perceived brightness depends on the system etendue limit, the efficiency of the light engine, and the source luminance. The ability to improve each of these parameters depends on the design constraints. The system etendue limit can be increased at the expense of bulkier, more complex, and more expensive designs. The light engine efficiency can be increased by using free-form shape components adapted to the shapes and the emission patterns of the considered LEDs. The apparent source luminance can be increased at the expense of the flux by either recycling light or restricting the light collection to a smaller etendue with higher average luminance. Luminance can also be increased by using multiple color primaries (spatial multiplexing) or pulsed LEDs (temporal multiplexing). Finally, we review how light recycling can be implemented to convert polarization without increasing etendue.

Designing freeform reflectors for extended sources

We propose a design method for single reflectors that takes into account extended sources with any arbitrary luminance distribution. This method is suitable for non-uniform prescribed illuminance distributions with arbitrary shapes. We use the method of supporting ellipsoids developed by Oliker in conjunction with optimization in order to control the effects of the source extent. Design examples related to street illumination and LED illumination are presented.

Method to improve spatial uniformity with lightpipes.

A heuristic method to obtain lightpipes that provide both collimation and good spatial uniformity is proposed. The change in shape that is likely to improve spatial uniformity, with minimal efficiency loss, can be predicted. Several case studies where this technique has been used are presented.

Freeform reflector design using integrable maps

We propose a design method for freeform reflectors based on source-target maps. The necessity for maps to fulfill the integrability condition to obtain a continuous reflector surface is discussed and demonstrated with various reflector geometries. We also review the advantages and drawbacks of reflectors with step discontinuities that do not require the integrability condition to be satisfied.

Optimization of single reflectors for extended sources

Reflectors for prescribed intensity or illuminance distributions are commonly used in luminaires and automotive headlights. However, their design has remained a challenge. Although reflector shapes are well known for a point source, the point source approximation leads to significant errors in the output distribution with extended and nonuniform source distributions. In practice, source non-idealities usually require the use of automated and manual optimization in the design process. We propose a hybrid optimization scheme that generates reflector shapes for rotationally symmetric systems and an arbitrary source luminance distribution. This method is based on an extension of the traditional algorithm for a point source, and uses a combination of an iterative algorithm and an optimization algorithm. Several case studies are presented.

Design of illumination devices for delivery of photodynamic therapy in the oral cavity

We present three designs for delivery of light in the oral cavity for photodynamic therapy (PDT) under the requirements of average irradiance of 50 mW/cm2 and spatial non-uniformities well under 10% over a square area of 25 mm2. The main goal is to design a device that avoids having to shield the oral cavity prior to irradiation for PDT. Illumination theory is instrumental in identifying an effective geometry for the device. The designs proposed build upon the technology that is already available for PDT and use illumination theory concepts to maximize the efficiency of the light delivery. One design combines a cylindrical diffusing fiber with a reflector derived from the edge-ray theorem while a second consists of a fiber illuminator coupled to a lightpipe device. Both designs are successful in delivering the light reducing the need of shielding and in providing the desired irradiance and uniformity. The two approaches performed comparably and provided a higher irradiance than needed, thus inspiring the design of a third, simpler design based on an off-axis cylinder reflector.

Beyond the desktop : emerging technologies for supporting 3D collaborative teams

The emergence of several trends, including the increased availability of wireless networks, miniaturization of electronics and sensing technologies, and novel input and output devices, is creating a demand for integrated, fulltime displays for use across a wide range of applications, including collaborative environments. In this paper, we present and discuss emerging visualization methods we are developing particularly as they relate to deployable displays and displays worn on the body to support mobile users.

Optimization of Freeform Non-Imaging Components for LED-Based Projector Light Engines

Standard non-imaging components used to collect and integrate light in LED-based projector light engines such as tapered rods and compound parabolic concentrators are compared to optimized freeform shapes in terms of various application-driven metrics.