Hüseyin Murat

Increased lumens per étendue by combining pulsed light-emitting diodes

LED-based projectors have numerous advantages compared to traditional projectors, such as compactness, larger color gamut, longer lifetime, and lower supply voltage. As LEDs can switch rapidly, there is the possibility to pulse. However, there is also an important disadvantage. The optical power per unit of etendue of an LED is significantly lower than, e.g., an ultra-high-performance (UHP) lamp. This problem can be remedied partly by pulsing the LEDs. If one drives an LED with a pulsed current source, the peak luminance can be higher, albeit the average luminance will not increase. By pulsing two LEDs alternately (50% duty cycle), their increased flux can be added up in time and will generate a higher average flux within the same etendue. We combine the LEDs with a polarizing beam splitter (PBS) and change the polarization of one LED with a switchable retarder. The achieved substantial net gain after all losses is 36%.

Two liquid crystal on silicon panel projector with efficient light-emitting diode illumination engine

LED-based projectors have numerous advantages compared to traditional projectors. They are more compact, they exhibit a larger color gamut and a longer lifetime, the supply voltage is lower and they can even operate on batteries. LEDs can switch rapidly (possibility to pulse) and they have a high dimming ratio (contrast considerations). However, they have low optical power per etendue, although this is also improving consistently. With an efficient illumination engine design we can build an LED projector with a moderate light output and with superior properties. We present a relatively compact LED projector with two liquid crystal on silicon (LCOS) light valves (LVs). One of these LVs alternately modulates red and blue information, while the other permanently modulates green information to achieve a good color balance. Additionally, we apply some methods to increase the brightness on the screen. Our two-LCOS approach results in a compact, efficient LED projector that produces 171 lm projected D65 flux.

Efficient and compact illumination in LED projection displays

In this paper we propose an efficient illumination engine for LED based projection systems. Our design had to be both compact and efficient. We designed the projector with two LCOS light panels. We investigate two phenomena that affect the optical efficiency of this projector. We show that a relevant gain of the light output can be obtained by using certain methods.

Demonstration of a polarization-based full-color stereoscopic projection display using liquid crystal on silicon panels and light emitting diodes

We present a single optical system that can simultaneously generate two linear polarized full-color images with orthogonal state of polarization. The system architecture of the optical core is discussed. Four liquid crystal on silicon panels are used to modulate both images. We also discuss the design of the illumination system with light emitting diodes as light sources. The contrast of both images is simulated. A proof-of-concept demonstrator is built and experimentally characterized. It is capable of two-dimensional and three-dimensional image display. Three-dimensional images can be perceived, independent of the tilt angle of the viewers head, by wearing specific polarization sensitive eyeglasses and placing a quarter-wave retarder at the projectors output. Important component specifications are overviewed to improve the performance of the demonstrator setup.