Micro-Display Vs. Scanning Mirrors Projectors
Two projection
mechanisms
Image generation from handheld projectors is possible using two basic projection
mechanisms: Micro-Displays and Scanning Mirrors:
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Micro-Displays allow the projection of the whole picture in its entirety (all the
picture's elements - pixels). This is the technology principle widely used today in
business and leisure (home-theater) projectors. |
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Scanning Mirrors allow the projection of images' built-up by a very fast
sequential 'flying spot' projection of single pixels. Scanning Mirror systems use
laser illumination as light source. |
Handheld Projector's Performance
For consumer electronics applications, performance as well as the manufacturing
costs, will ultimately determine the success of a technology. Specifically,
performance of a miniaturized battery operated personal projector will be measured
by: |
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Power efficiency in terms Lumens per Watt
- optical power output (Lumens) per Electrical input power (Watts); |
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Size and Form factor; |
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Color gamut and Image quality. |
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Lumens / Watt
The system’s overall power efficiency is the product of the efficiencies of the main
components along its optical path.
The Micro-Display architecture efficiency is made up of the combined efficiencies of
the (a) Micro-Display elements (LCD, LCOS or DLP); (b) Illumination source and; (c)
Other optical elements such as a focus lens or a polarizer required for LED based
illumination or a diffuser required for laser-based illumination.
Scanning Mirrors
Efficiency
The efficiency of the Scanning Mirror architecture is based on a smaller number of
components: (a) The modulated laser source and; (b) The reflective mirror(s)
mechanism.
Laser projection optics enables a 'focus free' solution thus saving the focus lens
mechanism, as well as the polarizer and the diffuser.
Micro-Display Efficiency
An Ultra High Performance Lamp (UHPL) illumination source is unsuitable for
miniaturized battery operated personal projector applications due to its power
consumption. The Micro-Display could instead be illuminated by LEDs or laser
sources.
An LED light source eases the power and heat dissipation constraints, however it
needs to be collimated (and also polarized when using LCOS).
The Micro-Display overall efficiency will then be dependent on the efficiency
elements of the LED sources, the collimator and the polarizer (when used).
If the Micro-Display uses a laser as its light source – the overall efficiency will be
dependent on the laser source and the accompanying diffuser.
The efficiency of the mirror’s mechanism reflective coating in the Scanning Mirrors
approach is better than the efficiencies of the polarizer or the diffuser in the Micro-
Display architecture.
Continuous Illumination
In addition a Micro-Display architecture requires a continuous laser/LED illumination
versus a Scanning Mirror system, in which the laser is basically modulated
according to the pixel information reducing to a minimum the power consumption.
Superior Efficiency
Therefore, the Scanning Mirror projector architecture results in a higher Lumen per
Watt metric regardless of the superior efficiency of the lasers source itself (over UHPL
and LEDs).
Miniaturization – Volume and Form Factor
| The "power of miniaturization" is another
performance benchmark dimension:
The Scanning Mirrors method is basically
"uni dimensional" in the sense that the
projected combined (RGB) beam spot is a
pixel's scale and the projected image is built
one pixel at a time. Comparably, the Micro-
Display architecture is inherently a planar
one - the projection "spot" is scaled by a
whole frame of pixels which is synchronously
projected. |
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Micro-Display volume implications
The requirement to increase the Micro-Display resolution is met with the need for
more pixels and thus more elements (such as micro-mirrors in a DLP chipset) which
results in an increase of the overall planar size. This has an impact on both (vertical
and horizontal) dimensions and consequently affects the overall system size.
The resolution achieved by the Micro-Display architecture is therefore related to the
overall size of the projection module.
In comparison increasing the resolution of the Scanning Mirrors alternative requires
a marginal increase of the reflective mirror size. The resolution of the Scanning
Mirrors architecture therefore has a marginal impact on the projector's size.
Manufacturing Cost
The manufacturing cost is another benchmark for the success of consumer
electronics products. The cost depends on: the number of elements involved, the
process complexity and scaling and the required accuracy.
Both the Micro-display and the Scanning Mirrors are manufactured based on MEMS
(Micro-ElectroMechanical Systems) technology. However while the Micro-Display wafer
is based on submicron accuracies, the Scanning Mirrors systems allow a simpler
production of bigger sub-elements.
Control circuitry
In addition to the costs difference of the optical elements, the control circuitry costs
are expected to be higher in the Micro-Display architecture.
Micro-Display control circuitry must process massive amounts of information as it
deals with the projection of the whole image frame. The Scanning Mirrors and
Laser control circuitry is comparatively much simpler as it monitors only the
sequential projection of a single pixel at a time.
Exceptional broad
color gamut
Among the other significant quality advantages that laser offers is its known broad
exceptional color gamut. Selecting Lasers of the saturated RGB primary colors
enables the coverage of over 90% of the Color Model and the human eye viewable
spectrum.
The Color Model below presents the available color gamut per specific display technology; CRT,
LCD, Plasma etc (e.g: CRTs are said to have a better color gamut than LCDs – meaning that their
projected colors are richer).
With the increased availability, reduced cost and increase in customer expectation
for true colors, it is not surprising that laser technology has begun to be used in the
TV industry.
Lasers, as diffraction limited light sources, don't require any focusing element thus
preventing the associated optical losses and reducing product size, while producing
an image which is always in focus. This quality is particularly relevant for mobile
applications, where motion is inherent in the user experience and projection
surfaces are inconsistent or even curved.
Summary
The Scanning Mirrors approach provides system simplicity, enables superior overall
optical efficiency, optimal miniaturization, as well as better color gamut, all with
lower manufacturing costs.
Scanning Mirrors technology is therefore best suited to drive the promising mass
market of miniature personal projector applications.
Current Micro-Display technologies have reached a miniaturization level where next
step challenges need to be addressed from a new angle - Scanning Mirrors and
Lasers technology provide this leap forward.
Zeppelin has an important role in the birth of aviation, though it is the airplane which
had carried us to our times…
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