Development of the Nitride Laser Diode Arrays for Video and Movie Projectors
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Development of the Nitride Laser Diode Arrays for Video and Movie Projectors Piotr Perlin,1 Szymon Stańczyk1, Steve Najda2, Tadek Suski1, Przemek Wiśniewski1,2, Irina Makarowa2, Łucja Marona1,2, Anna Kafar1, Agata Bojarska1, Robert Czernecki1,2 , Robert Sarzała3, Maciej Kuc3, Mike Leszczynski1,2 1 Institute of High Pressure Physics, “Unipress”, Sokołowska 29/37, 01-142 Warsaw, Poland 2 TopGaN Ltd, Sokołowska 29/37, 01-142 Warsaw, Poland 3 Lodz, University of Technology, Łódź, Poland ABSTRACT We demonstrated the fabrication of 10 emitters InGaN laser diode array of the maximum output power of 9 W at 420 nm. The device as a whole has the differential efficiency of above 1 W/A. The maximum output power is limited to 9 W (pulse operation) by catastrophic mirror damage or to around 5 W in CW operation by thermal roll-over. Larger arrays with stripes width of around 15 μm and numbers of emitters up to 20 should enable reaching 20 W, which is suitable for light engine of desktop projectors and a building block of cinema theater projectors. INTRODUCTION The advent of video, multicolor projectors with the light engine built of the set of blue nitride laser diodes clearly marks the possibility of replacing mercury and xenon lamp in yet another application. But this is not a simple replacement; the laser light is bringing here unbeatable colors and excellent energetic economy. However, as these video and movie projectors requires very high optical power, from 20 up to 200 W, the laser source of the light must meet strong requirements concerning the optical power, beam quality, light polarization and economy of production and use1. For optical projectors, which make use of Digital Light Processing (DLP) technology the ideal sources of light, characterized by a very high optical power, are laser diode arrays, which combine compact construction, strong, linearly polarized light, and economy. However, the optimum design of such devices must take into account specific features of GaN based devices, like from one side relatively high contact resistance and from the other side very high GaN substrate thermal conductivity. Within this presentation we will discuss the issues related with the optimization of such leading to fabrication of the devices with the optical power exceeding 10 W. The maximum optical power for semiconductor laser diodes is limited by two effects: thermal roll of the light-current (L-I) characteristic and catastrophic optical damage of laser facets (COMD). The first of this effect is visualized in Fig. 1. This graph shows the example of real L-I characteristic and simulation showing the relation between the thermal resistance (Rtherm) of the device and the roll-off current. This relation is calculated using Equations 1, 2 and 3. 2
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Figure 1. a) An exemplary behavior of an narrow stripe InGaN laser diode and b) L-I characteristic calculated for the various values of laser diode thermal resistance basing on Eq. 1,2 and 3.
Ithr=I0exp(T/T0)
(1)
T=T0+Rtherm⋅I⋅V
(2)
P=(I-Ithr) ⋅η
(3)
Here Ithr is a thresho
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