Abstract
In this paper, the relationship between the coherence and the
speckle contrast in a laser-based projection display system is studied
with the consideration of human visual percept. By using a varifocal
liquid-crystal lens and a monochromatic charge-coupled device (CCD),
a system which is used for simulating a human eye is set up to record
the speckle pattern. An efficient method for controlling the spatial
coherence by using a dielectric elastomeric actuator (DEA) is demonstrated.
We find that there is a limitation for eliminating the speckle contrast
in the laser projection system when only the method of reducing the
spatial coherence is used. When the distance between the observer
and the screen is sufficiently large (
${>} {3 m}$
), the speckle
contrast can be eliminated well (
${<} {{4}}\%$
) by reducing
the spatial coherence and the observer do not observe the speckle
phenomenon. When the viewing distance is smaller than 3 m, however,
the observer will feel the speckle all of the time. To further reduce
the speckle contract, a method of wavelength modulation is used to
reduce the temporal coherence while the spatial coherence is well
reduced. The speckle contrast is reduced to 4% at the viewing distance
of 1 m by reducing both the temporal and spatial coherence of the
laser.
© 2015 IEEE
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