Whither Pico Projectors?
by Robert L. Melcher
The current interest in pico projectors presents an interesting confluence between technology-driven product development and market-driven product requirements. Despite this favorable circumstance, the eventual commercial success of these products remains yet uncertain. The pico projector is the natural evolution of projector technology ranging from the large-venue projectors providing tens of thousands of lumens, through conference-room products providing a few thousand lumens, to portable products providing about one thousand lumens, to pocket projectors providing several tens to a few hundred lumens, and now to pico projectors for which ten or so lumens is a reasonable objective for a very small battery-operated portable device.
There appears to be little market doubt that the consumer and professional would embrace a portable display device which is the physical size of a cell phone, but produces a useable image the size of a laptop display on almost any surface. Of course, the price will have to be right and the power consumption low enough to have a useful battery life. Thus far, head-mounted displays, which claim these features, have failed to catch on in any significant way except for certain niche applications; probably because of ergonomic inconvenience and cost/benefit trade-offs. The latest attempts to serve this presumed market are pico projectors, which are the subject of the four papers in this issue ofInformation Display.
The technological developments addressing this market objective have been substantial in recent years. These include the development and use of both LED and laser light sources, the development of high-resolution highly integrated LCOS imaging devices with tiny pixels and hence low manufacturing cost, the development of small and fast MEMS light reflectors and scanners, new small low-cost optical elements to help create and control the image, novel forms of image generation, and, finally, the continued development of low-cost low-power video-processing capability.
The first paper in this issue is from Insight Media and describes the market opportunity for pico projectors with emphasis on cell phones and PDAs. Both stand-alone pico projectors as well as those embedded or integrated as part of the portable device are considered. The conclusion is that the market opportunity is huge, if and when products are offered which meet the technical and cost requirements while being ergonomically satisfying.
An example of new pico projectors, which have arrived in the market this year, is the Optoma EP-PK-101, which is based on a color-sequential Texas Instruments DLP pico micromirror device. Another is the MPpro 110 from 3M, based on a Himax LCOS micro-display with integrated color filters. Both products use LED illumination and are about the size and weight of an iPhone. The 3M product utilizes novel multi-functional low-cost acrylic polymer optical prism elements with 3M multilayer optical film technology.
The following three papers are examples of some of the exciting new technological approaches currently under development, which have the goal of providing successful pico-projector products.
The paper from Displaytech covers a high-speed LCOS device suitable for color-sequential application and based on ferroelectric liquid-crystal materials. The design includes color-sequencing and frame-buffering circuitry on the microdisplay back plane, demonstrating the potential of LCOS to reduce system size, power, and cost. The authors analyze and compare the efficiency of color-filter array versus color-sequential pico-projector systems. They also compare theefficacy, lm/W, for the color-sequential systems utilizing both LCOS and MEMS-based micro-display technology and provide a roadmap for future LED and microdisplay developments.
Light Blue Optics takes a very different approach to developing a pico projector in thethird paper of this issue. They generate imagesby computing sets of statistically independentholograms corresponding to the desired image, which are then displayed at several times the video frame rate on a high-speed LCOS micro-display. The microdisplay, used as a two-dimensional phase-only diffraction grating, is illuminated by pulsed R, G, B lasers. The system achieves high efficiency because the diffracted light is steered into the desired pixels, without absorption, to form the desired image. By using a number of techniques, including driving the microdisplay at several times the video frame rate, speckle caused by the coherence of the laser illumination is reduced.
In the final paper, Microvision takes yet another fundamentally different approach to pico-projector technology. Instead of using a high-resolution imaging device, i.e., LCOS, DLP, etc., they use a unique single-element MEMS mirror to scan nanosecond R, G, B laser light in two dimensions and thereby construct an image. Because of the high collimation of the lasers, the depth of field of the image is very large, resulting in simplificationof the optical design and application flexibility. Like the CRT, image-format flexibility is anotherfeature of a scanned-beam display system.
The market opportunity coupled with the novel and varied technological approaches make the pico-projector field one of the most dynamic areas of current display development. This issue of Information Display provides a sampling of the status of the development work in this field.Additional significant work is ongoing in labo-ratories around the world. The technology and the market should converge in the next year or two. Either pico projectors will form the basis of a significant new display market or they will possibly recede back to low-volume niche applications. The first products of this exciting endeavor should appear soon; their market acceptance will be a harbinger of the future.