With the pressure to reduce cost for mass-market introduction of microdisplay-based rear projection television (MD-RPTV), the image panel and the related optical components have to be reduced in size and novel optical arrangements have to be created to achieve the target price. One major issue always had been the need for more light. Traditional reflector systems, including elliptical and parabolic reflectors, perform well in most cases, but are inefficient for smaller etendue values corresponding to smaller image panels. The common remedy is to make lamps with shorter and shorter arcs to increase the coupling efficiency, but the corresponding lifetime of the lamps are reduced and most of the time, these short arc lamps can only operate at low power, thus limiting the total output of the illuminating system. This paper summarizes the progress in the last few years related to the dual Paraboloid reflector (DPR) system and the associated components including polarization recovery systems and light pipe based projection engines.
Traditional projection engine designs are mostly based on propagation of light through standard components, such as, dichroic filters, lenses, polarization beam splitters, prisms, etc. These components are usually held individually using optical mounts and assembled together on an optical bench such that all the components are aligned properly. Even in high volume production environment, it tends to be tedious and expensive. With the advancement of light pipe based illumination system, e.g. the Wavien patented dual paraboloid reflector system, and light-pipe based polarization recovery system, it would be advantage to design a light-pipe based projection engine for a complete light-pipe based system for low cost and space saving applications. Except the projection lens, a totally light-pipe based projection engine is described. It consists of an etendue efficiency illumination system using the dual paraboloid reflector system with a lensed tapered light pipe at the output. The output is then directed into a light-pipe based polarization recovery system such that the output is polarized. The polarized light is then separated into its individual RGB colors, and is directed into the corresponding HTPS imager chips separately by the use of light pipes, prism, and beam splitters. The outputs from the imager chips are then recombined by an X-cube and projected onto the screen. A design has also been made for LCOS imagers. The folding and unfolding properties of the light pipe are used in this case resulting in a more compact projection engine. This light-pipe based system uses low cost optical components and takes up much less space than the traditional projection system.
One of the important properties to the emission of light from a side lighting waveguide using a notched cladding and solid core is the numerical aperture of the source at the input of the fiber core. Reducing the emission angle of light entering the fiber allows light transmission further down the fiber so that it becomes available for side emission at an increased distance from the source. This allows side-lighting fibers to be made longer and more uniform. Utilizing this effect, the fiber can be notched in a controlled manner that efficiently converts the source light accepted into the waveguide into a side-emitted light that is distributed uniformly over the length of the fiber. A detailed optical analysis of this system will be presented with evaluation of the effect on the resulting side light emission as the source light parameters are adjusted. The analysis will include discussions on the trade-off associated with the reduced source efficiencies at lower etendue values and the optimization of the system as a whole. Experimental results using a metal halide arc lamp with dual parabolic reflector as the source and solid-core polymer fiber of 12-18 mm diameter with customized notched cladding will be presented and discussed.
In illumination systems for projection display, it is often necessary to tailor the aperture size and angle of light to suit the system requirements such as an imager panel. One way to do that is to use lenses, but depending on the angle and area this may not be achieved economically in terms of space and costs. Non-imaging optics is often used to perform such function. A compound parabolic concentrator (CPC), which is simple to use and small in size, is one example of such approach, but it has the disadvantage of non-uniform output intensity profile and not conserving brightness. A tapered light pipe (TLP) is often used instead to alleviate such shortcomings, but such light pipe would need to be infinitely long to conserve brightness, which makes it quite impractical. In this paper, a lensed tapered light pipe is described that change the area and angle of light with minimal loss of brightness and provide a very uniform output intensity profile at the output. Numerical modeling using ray tracing computer program is used to optimize the TLP for each applications.
The Wavien's dual paraboloid reflector system improves the output brightness of an illumination system by preserving the brightness of the arc. We present steps for optimizing a projection engine illumination system using this reflector system and an output tapered light pipe. The output from the light pipe is then fed into a supercube polarization recovery system for its freedom from problematic wave plates. Ray-tracing software is used to optimize the components, including the dual paraboloid reflector parameters and the supercube polarization recovery system. The model shows agreements with the experimental results and is suitable for designing and predicting future system performance.
Projection engine designs are mostly based on discrete optical components including color filters, mirrors, relay lenses, prisms, etc., which tends to be expensive and increase the space requirement. With the advancement of light pipe based illumination system, e.g. the Wavien patented dual paraboloid reflector system, and light-pipe based polarization recovery system, it would be advantage to design a light-pipe based projection engine for a complete light-pipe based system for low cost and space saving applications. In this paper, a totally light-pipe based projection engine is described. It consists of an etendue efficiency illumination system using the dual paraboloid reflector system with a lensed tapered light pipe as the output. The output is then directed into a light-pipe based polarization recovery system such that the output is polarized. The polarized light is then separated into its individual RGB colors, and is directed into the corresponding HTPS imager chips separately by the use of light pipes, prism, and beam splitters. The outputs from the imager chips are then recombined by an X-cube and projected onto the screen. This light-pipe based system uses low cost optical components and take up much less space than the traditional projection system.
A dual paraboloid reflector system conserves the source brightness by producing a real image of the arc on the target space. Traditional elliptical and parabolic reflector tends to degrade the brightness of the arc due to the angular dependence of the magnification such that the image at the target space is the superposition of multiple images of the arc with varying degree of magnifications. In this paper, we present steps for optimizing a projection illumination system consisting of the dual paraboloid reflectors. The effects of various parameters including reflector sizes, scattering and angular extents were evaluated using ray-tracing model. The results of the calculations are compared with experimental measurement.
With the increased interests in mass production of LCD, LCOS and DLP microdisplay-based projectors and televisions, the image panel sizes become smaller and requires more efficient coupling of light from the source to the image panel. At the same time, the demand for high-energy efficient general illumination system also requires efficient coupling of light from a light source into fiber optics. To illuminate these smaller image panels and fibers efficiently, a patented dual paraboloid reflector system has been developed to collect and focus light from an arc lamp onto the targeted application without loss of brightness. Arc lamps with longer arc lengths can be used, which are usually easier to make and have longer life. The dual paraboloid reflector1,2 system consists of two parabolic reflectors placed symmetrically facing each other. The first parabolic reflector collects and collimates light into a parallel beam. The second parabolic reflector intercepts the parallel beam and focuses the light into a lensed rectangular tapered light pipe (TLP) resulting in a unity magnification, i.e. 1:1 imaging, with conserved brightness. Due to the unique nature of 1:1 imaging of the system, together with the retro-reflector, the folding of the arc to increase brightness will also be described. The TLP transforms the focused light into an output with the needed area, shape, and numerical aperture. It also acts as a homogenizer so that the intensity profile at the output surface is uniform and eventually provides a uniform intensity profile at the screen or at the input face of the fibers. The reflection of light twice in the dual paraboloid reflector system provides high IR and UV rejection ratios, resulting in less degradation of the optical components and fibers. ASAP models of the system and experimental results will be presented. The shape of the etendue curve also provides higher efficiency in using polarization recovery system. Several patent-pending light-pipe-based polarization recovery and recycling systems, will be discussed. Calculation and experimental results will also be presented.
Micro display devices such as LCOS and DLP(tm) have capitalized on advancement of microelectronics fabrication technologies. Device miniaturization has created a need for high brightness light sources having low numerical apertures. Light sources based on the traditional non-imaging principles such as an ellipsoidal reflector require lamps emitting nearly a point-like source, which prompted reduction of arc sizes and increase in fill pressure in arc lamps. These requirements shorten the life and increase the cost of the lamp. In this paper, we present a novel illumination system that is based on a one-to-one imaging principle. The approach incorporates a so-called Dual Paraboloid Reflector (DPR) system in which two halves of paraboloid reflectors and a hemispherical retro-reflector are used to collect almost all the light emitted from an arc lamp. When combined with a tapered light pipe (TLP), a DPR based illumination system produces a light output having a required area, shape, numerical aperture, and a high and uniform flux density. Contrary to methods based on non-imaging principles DPR illuminators do not require those short lived short arc lamps to satisfy the needs of the projection industry. ASAP simulations of the system and experimental results are presented. The advantages of this system when applied to polarization recovery, polarization recycling, and color recycling will be discussed.
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