After the invention of lasers, in the past 50 years progress made in laser-based display technology has been very promising, with commercial products awaiting release to the mass market. Compact laser systems, such as edge-emitting diodes, vertical-cavity surface-emitting lasers, and optically pumped semiconductor lasers, are suitable candidates for laser-based displays. Laser speckle is an important concern, as it degrades image quality. Typically, one or multiple speckle reduction techniques are employed in laser displays to reduce speckle contrast. Likewise, laser safety issues need to be carefully evaluated in designing laser displays under different usage scenarios. Laser beam shaping using refractive and diffractive components is an integral part of laser displays, and the requirements depend on the source specifications, modulation technique, and the scanning method being employed in the display. A variety of laser-based displays have been reported, and many products such as pico projectors and laser televisions are commercially available already.

/pdf/laser-based-displays-a-review-4g00j2f2g3.pdf

Laser-based displays: a review

The theory of speckle noise in a scanning beam is presented. The general formulas for the calculation of speckle contrast, which apply to any scanning display, are obtained. It is shown that the main requirement for successful speckle suppression in a scanning display is a narrow autocorrelation peak and low sidelobe level in the autocorrelation function of the complex amplitude distribution across a scanning light beam. The simple formulas for speckle contrast for a beam with a narrow autocorrelation function peak were obtained. It was shown that application of a diffractive optical element (DOE) with a Barker code phase shape could use only natural display scanning motion for speckle suppression. DOE with a Barker code phase shape has a small size and may be deposited on the light modulator inside the depth of the focus of the reflected beam area, and therefore, it does not need an additional image plane and complicated relay optics.

Speckle suppression in scanning laser display.

A tunable grating using viscoelastic PDMS (polydimethylsiloxane) and conductive polymer PEDOT (poly 3,4-ethylenedioxythiophene): PSS (polystyrenesulfonate) was designed and the fabrication process was developed. A sandwich structure (PEDOT: PSS/PDMS/Gold electrode) was utilized. By applying voltage between the PEDOT: PSS top film and the bottom interdigital gold electrode, the initial plane surface of polymers deforms into a sinusoidal grating. The PDMS material properties were tuned by modifying the network structure to obtain good actuation of the polymer, including large relief depth and fast response speed. The grating profile on the surface was observed with the maximum relief depth of 200 nm. The response time of the modulator can reach 250 μs.

A novel tunable grating fabricated with viscoelastic polymer (PDMS) and conductive polymer (PEDOT)

A diffractive optical MEMS device for spatial and temporal light modulation is described that is capable of high-speed digital operation. The device contains electromechanical ribbons suspended flat above a silicon substrate by a periodic series of intermediate supports. When actuated electrostatically, the ribbons conform around the support substructure to produce a grating. The device has optical switching times of less than 50 nsec, sub-nanosecond jitter, high optical contrast and efficiency, and reliable actuation in contact mode. The fine gray levels needed for digital imaging systems are produced by pulse width modulation.

Conformal grating electromechanical system (GEMS) for high-speed digital light modulation

Time-dependent deformation (creep) behaviors of piezoelectric microactuators have been investigated. Position (or gap height) drift of microbridged actuator beam and its displacement amplitude change with time could be attributed to the anelastic behavior of the driving unit itself based on lead zirconate titanate (PZT) in the actuator, and as well as to the mechanical stress states established in the microactuator beam after the surface release of the micromachined actuator structure. From creep analyses of a simple microcantilever and microbridge beam structures, it was turned out that the overall creep behavior in microbridged piezoactuator structure was mainly dependent on the actuator beam initial deflection configuration governed both by residual stress of the actuating part Pt/PZT/Pt stack and the stress gradient through the silicon nitride (SiNx) microbridge beam.

Creep behavior of undoped and La–Nb codoped PZT based micro-piezoactuators for micro-optical modulator applications

A diffractive optical modulator has been fabricated based on a micromachining process. Novel
properties of its fast response time and dynamics were fully understood and demonstrated for the
strong potentials in embedded mobile laser display. Bridged thin film piezo-actuators with so called
open mirror diffraction structure has been designed. Optical level package also was achieved to
successfully prove its display application qualities. Display circuits and driving logic were developed
to finally confirm the single-panel laser display at a 240Hz VGA (640×480). With its efficiency of
more than 75% and 13cc volume optical engine with the MEMS-based VGA resolution SOM
showed 7 lm brightness at a 1.5W electrical power consumption. Detailed design principle,
fabrication, packaging and performances of the invented SOM are described.

A novel diffractive micro-optical modulator for mobile display applications

A new type of diffractive spatial optical modulators, named SOM, has been developed by Samsung Electro-Mechanics
for laser projection display. It exhibit inherent advantages of fast response time and high-performance light modulation,
suitable for high quality embedded laser projection displays. The calculated efficiency and contrast ratio are 75 % and
800:1 respectively in case of 0 th order, 67 % and 1000:1 respectively in case of ±1st order. The response time is as fast as
0.7 ms. Also we get the displacement of 400 nm enough to display full color with single panel in VGA format, as being
10 V driven. Optical module with VGA was successfully demonstrated for its potential applications in mobile laser
projection display such as cellular phone, digital still camera and note PC product. Electrical power consumption is less
than 2 W, volume is less than 13 cc. Brightness is enough to watch TV and movie in the open air, being variable up to 6
lm. Even if it's optimal diagonal image size is 10 inch, image quality does not deteriorate in the range of 5 to 50 inch
because of the merit of focus-free. Due to 100 % fill factor, the image is seamless so as to be unpleasant to see the every
pixel's partition. High speed of response time can make full color display with 24-bit gray scale and cause no scan line
artifact, better than any other devices.

Spatial optical modulator (SOM): high-density diffractive laser projection display

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A novel diffractive micro-optical modulator for mobile display applications

Spatial optical modulator (SOM): high-density diffractive laser projection display