ABSTRACT
New laser-based light sources are highly desired for projection displays because of the need for longer lifetime, lower etendue, and higher color gamut. High power, frequency doubled red, green and blue (RGB) surface emitting diode laser arrays have been developed for use in low cost projection microdisplay televisions.
INTRODUCTION
Novalux [1] has been developing low-cost projection display light sources using its patented semiconductor laser technology based on high-power, cavity-controlled surface emitting diode lasers that emit circular Gaussian beams (NECSEL: Novalux Extended Cavity Surface Emitting Laser). The Necsel provides an efficient, frequency-doubled source of laser radiation in the red, blue and green using InGaAs-based infrared semiconductor laser material together with periodically poled lithium niobate (PPLN). These devices have the potential for achieving the price and performance requirements of consumer projection display applications. Necsel arrays have operated in the visible with more than 3.5 W of average power in the blue (465-nm) and green (532-nm) and more than 1.2W in the red (621-nm).
ADVANTAGES FOR DISPLAYS
Lasers offer significant advantages as light sources for displays due to their large color gamut, high brightness, ability to be current modulated for gray scale, long lifetime and low manufacturing cost. The high brightness of lasers (~ 5x106 times that of LEDs) allows the use of the smallest possible micro-displays, low screen gain and power levels that outperform lamps or light emitting diodes. Necsel technology will also offer constant lumen output over the life of the system without wavelength shift over time. Necsels can be operated as small single emitters that can be directly modulated for use in scanning displays as well as very high power arrays for cinema, home TV and signage applications. The output from Necsels are polarized which makes them ideally suited for use with liquid crystal micro-displays or back-light units (BLU) for LCD TVs.
The narrow composite beam angle from such arrays will allow use of optical systems that will provide > 50-inch screens with display thickness comparable to plasma TVs but much lighter and 1/3 the power consumption. Figure 1 shows such an example for a rear projection display recently demonstrated by Mitsubishi. This will bring RPTV to a superior price/performance with plasma displays.
Single-beam or small array formats will allow personal (pocket) displays with output of a few hundred lumens. The high-speed modulation capability of Necsels can provide gray scales suitable for video images and head-up displays. A single beam Necsel has already been used in a 100cc RGB single-beam projection display (see Figure 2). Future applications include use with cell phones, automobile head-up and dashboard displays, as well as being the ultimate display for high definition gaming boxes.
The additional advantages of Necsels include wider color gamut, use of the smallest possible (and therefore cheaper) micro-displays, the elimination of many optical components, polarized output and the use of a high f (>f/9) number projection lens for reduced cost optics.
Figure 1. Photo of 52-inch HD laser RPTV announced by Mitsubishi having 500 nits, 4000:1 contrast and thin form factor using a DLP.
Figure 2. Photograph of a 20-lumen "pico-projector" using a MEMS scanner made by Microvision, Inc. The green laser is a single-element Necsel.
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