Gero Heusler

UHP lamp systems for projection applications

Projection systems have found widespread use in conference rooms and other professional applications during the last decade and are now entering the home TV market at a considerable pace. Projectors as small as about one litre are able to deliver several thousand screen lumens and are, with a system efficacy of over 10 lm W −1 , the most efficient display systems realized today. Short arc lamps are a key component for projection systems of the highest efficiency for small-size projection displays. The introduction of the ultra high performance (UHP) lamp system by Philips in 1995 can be identified as one of the key enablers of the commercial success of projection systems. The UHP lamp concept features outstanding arc luminance, a well suited spectrum, long life and excellent lumen maintenance. For the first time it combines a very high pressure mercury discharge lamp with extremely short and stable arc gap with a regenerative chemical cycle keeping the discharge walls free from blackening, leading to lifetimes of over 10 000 h. Since the introduction of the UHP lamp system, many important new technology improvements have been realized: burner designs for higher lamp power, advanced ignition systems, miniaturized electronic drivers and innovative reflector concepts. These achievements enabled the impressive increase of projector light output, a remarkable reduction in projector size and even higher optical efficiency in projection systems during the last years. In this paper the concept of the UHP lamp system is described, followed by a discussion of the technological evolution the UHP lamp has undergone so far. Last, but not least, the important improvements of the UHP lamp system including the electronic driver and the reflector are discussed. (Some figures in this article are in colour only in the electronic version)

Discharge efficiency in high-Xe-content plasma display panels

We study theoretically the overall output performance and the dominating reaction processes of the vacuum ultraviolet (UV) radiation production in high-Xe partial pressures in plasma display panels (PDPs) with Ne–Xe gas mixtures. A two-dimensional self-consistent fluid model is applied for the simulations of discharges and UV radiation in sustaining phases of PDPs. The UV intensity increases with the Xe partial pressure (PXe). The discharge efficiency also increases with PXe. The resonant radiation from Xe(3P1) dominates for 3.5%, while that from Xe2(3Σu+) becomes dominant over Xe(3P1) for 10%–30%. Remarkably for 30%, the intensity from Xe2(1Σu+) is even larger than that from Xe(3P1). It is found that for higher PXe, the UV radiation mainly consists of the excimer radiation from Xe2(1Σu+) and Xe2(3Σu+). Here, Xe(3P1) does not play a role itself as the UV radiator of the resonant radiation (147 nm), but as the precursor to Xe2(1Σu+), which results in the excimer radiation (173 nm).

Modular VCSEL solution for uniform line illumination in the kW range

High power VCSEL arrays can be used as a versatile illumination and heating source. They are widely scalable in power and offer a robust and economic solution for many new applications with moderate brightness requirements. The use of VCSEL arrays for high power laser diode applications enables multiple benefits: Full wafer level production of VCSELs including the combination with micro-optics; assembly technologies allowing large synergy with LED assembly thus profiting from the rapid development in solid state lighting; an outstanding reliability and a modular approach on all levels. A high power VCSEL array module for a very uniform line illumination is described in detail which offers >150W/cm optical output and enables less than 1% non-uniformities per mm along the line. The applied optical principle of near field imaging and massively superposing many thousand VCSELs by arrays of micro-lenses gives perfect control over the intensity distribution and is inherently robust. A specific array of parallelogram shaped VCSELs has been developed in combination with an appropriate micro-lens design and an alignment strategy. The concept uses parallel and serial connection of VCSEL arrays on sub-mounts on water coolers in order to realize a good combination of moderate operating currents and reliability. Lines of any desired length can be built from modules of 1cm length because this optical concept allows large mounting tolerances between individual modules. Therefore the concept is scalable for a wide range of applications. A demonstrator system with an optical output of 3.5kW and a line length of 20cm has been realized.

High-power VCSEL systems and applications

Easy system design, compactness and a uniform power distribution define the basic advantages of high power VCSEL systems. Full addressability in space and time add new dimensions for optimization and enable “digital photonic production”. Many thermal processes benefit from the improved control i.e. heat is applied exactly where and when it is needed. The compact VCSEL systems can be integrated into most manufacturing equipment, replacing batch processes using large furnaces and reducing energy consumption. This paper will present how recent technological development of high power VCSEL systems will extend efficiency and flexibility of thermal processes and replace not only laser systems, lamps and furnaces but enable new ways of production. High power VCSEL systems are made from many VCSEL chips, each comprising thousands of low power VCSELs. Systems scalable in power from watts to multiple ten kilowatts and with various form factors utilize a common modular building block concept. Designs for reliable high power VCSEL arrays and systems can be developed and tested on each building block level and benefit from the low power density and excellent reliability of the VCSELs. Furthermore advanced assembly concepts aim to reduce the number of individual processes and components and make the whole system even more simple and reliable.

26.2: Controlled Electrodes in UHP Lamps

The electrodes of short arc UHP lamps bear the brunt to combine high power densities with long life. This conflict can be resolved by a proper electrical operation of the lamp. Special drive schemes for Philips UHP lamps provide a stable arc attachment and a superior electrode durability. In this paper, we present electrode performance measurements under various conditions and discuss the underlying physical effects.

UHP lamps for projection systems: getting always brighter, smaller, and even more colorful

The past decade has seen a rapid development of projection systems. Projectors as small as only a few liters in size deliver several thousand screen lumens and are, with an efficacy of over 10 lm/W, the most efficient display systems realized today. This has been made possible by breakthroughs in lamp technology, particularly by the development of the UHP-lamp. This broadband light source with its outstanding brightness and lifetimes of over 10000 hours is ideal for projection applications. In this paper we want to describe three major technological trend lines in the development of UHP-lamps over the past decade: First, there is a trend towards brighter projectors, which is fostered by a brightness increase of the UHP-lamps. At the same time, projectors have seen a dramatic reduction in size, which has been made possible mostly by reducing lamp- and driver-size by even a factor of 10. This was only possible by the development of new ignition concepts as well as new optical designs of the reflector. And finally, UHP-lamps have seen quite some improvement in color rendering by using even higher pressures and shorter arc gaps. This allows for more colorful pictures and even more efficient projector designs.

Design of high power VCSEL arrays

High power VCSEL arrays can be used as a versatile illumination and heating source. They are widely scalable in power and offer a robust and economic solution for many new applications with moderate brightness requirements. The design of high power VCSEL arrays requires a concurrent consideration of mechanical, thermal, optical and electrical aspects. Especially the heat dissipation from the loss regions in the VCSEL mesas into the surrounding materials and finally towards the heat sink is discussed in detail using analytical and finite element calculations. Basic VCSEL properties can be separated from the calculation of thermal resistivity and only the latter depends on the details of array design. Guidelines are derived for shape, size and pitch of the VCSEL mesas in an array and optimized designs are presented. The electro-optical efficiency of the VCSELs and the material properties determine the operation point. A specific VCSEL design with the shape of elongated rectangles is discussed in more depth. The theoretical predictions are confirmed by measurements on practical modules of top-emitting structures as well as of bottom-emitting structures.

16.1: UHP Lamps with Increased Efficiency

Shorter arcs and higher gas pressures increase the collection efficiency and produce a spectrum which is ideal for video projection. Taking into account the physical lamp efficiency ideal arc lengths are given. New UHP products will realise 30% more light on the screen.

Advanced UHP lamps for projection systems

Projection systems for large screens have made tremendous progress during the last years, both in terms of performance and size reduction. Improved UHP lamp systems made a major contribution to enable the new generation of projectors. The arc gap is reduced to 1 mm only and allows a high collection efficiency in the projector. At the same time the lamp wattage was increased. In this way, todays projectors can create high-quality XGA pictures with more than 3000 screen lumens using one single 200 W UHP-lamp. Such a projector reaches an efficiency of more than 10 screen lumens per watt electrical input power. The volume of lamp and driver has been reduced by one order of magnitude during the last six years. This was possible by recent progress that has been achieved on the ignition of the lamp. By using a UV-enhancer cavity in the lamp seal and an additional antenna the ignition voltage could be reduced from 20 kV to below 5 kV. This allows more compact drivers and is ideal for miniaturizing projectors. A new optical concept allows for extremely compact reflector systems: A dichroic coating applied to one half of the UHP burner focuses all light into one hemisphere. Additionally 20-30% more light can be collected in systems with high optical demands. Making use of both the reduced ignition voltage and the new optical concept a reduction of the volume of lamp and driver by a factor of 10 has been realized.

Optical components and optical systems for VCSEL diode laser systems

Abstract High power vertical-cavity surface-emitting laser (VCSEL) arrays can be used as a versatile illumination and heating source. They are widely scalable in power and offer a robust and economic solution for many new applications with moderate brightness requirements. The use of VCSEL arrays for high power laser diode applications enables multiple benefits: full wafer level production of VCSELs including combination with micro-optics; assembly technologies allowing large synergy with LED assembly thus profiting from the fast development in solid state lighting; outstanding reliability and a modular approach on all levels. With the use of μ-lenses, the described optical principle of near field imaging and superpositioning of many thousands of VCSELs gives perfect control over intensity distribution and is inherently robust. With a slightly modified approach, lines of any desired length can be built from modules of 1-cm length and are therefore scalable for a wide range of applications.