Cellophane turns LCDs 3D
By Eric Smalley, Technology
items have more to them than meets the eye.
For the past couple of decades research teams have worked to make
various types of three-dimensional displays; most methods include fairly
A researcher from the University of Toronto has taken a different
tack. As it turns out, a trip to the kitchen and a pair of polarizing glasses
can turn an ordinary laptop screen into a 3D display.
The method could lead to extremely low-cost three-dimensional applications
for scientific and medical imaging, and for games, according to Keigo Iizuka,
a professor emeritus of electrical and computer engineering at the University
Iizuka's tests verified that a sheet of ordinary cellophane possesses
the properties necessary to rotate the direction of white light polarization
90 degrees. Polarization has to do with the electric field of a lightwave.
This electric field vibrates in a plane perpendicular to the direction of
the light beam, and polarized light vibrates in only one direction in this
plane. Glare is light that becomes horizontally polarized by reflecting
off a surface, and sunglasses work by blocking horizontally-polarized light.
The combination of a computer screen showing two copies of an image
that are polarized differently and a pair of glasses that blocks light polarized
in different directions for each eye, will allow a viewer to see a different
copy of the image with each eye.
This creates the illusion of three dimensions because the human
brain judges distances based on the differences in the views seen by each
Iizuka's method takes advantage of a property of the liquid crystal
displays used in laptops and flat screen monitors. The top layers of the
displays are polarizer sheets, which block polarized light that has been
rotated by the liquid crystals that form characters and other marks on the
screen, but let through the background light that remains polarized parallel
to the polarizer sheets.
Because the light coming from a screen is already polarized, it
is possible to rotate the polarization of the light coming from one half
of the screen 90 degrees by simply covering that side with cellophane, said
Iizuka. "The advantage of such a 3D display is that it is easy to fabricate
with readily available components at minimum cost," he said.
The colorless, 25 micron-thick cellophane the researchers tested
was better than the commercial half-wave plates usually used for the job,
according to Iizuka. "Cellophane's performance in rotating the direction
of polarization of white light was superior to that of commercially available
half-waveplates designed for a specific wavelength," he said.
Half-waveplates of the size needed to turn a laptop into three-dimensional
display also cost 3,500 times that of an appropriately-sized sheet of cellophane,
Cellophane's polarization properties are a byproduct of the strain
it bears during its fabrication process. Cellophane is made by extruding
a cellulose solution through a narrow slit into an acid bath, said Iizuka.
The unidirectional strain during the extruding process makes cellophane
an anisotropic material that behaves like a calcite crystal, he said.
Anisotropic materials, which include wood, contain physical properties
that are different in different directions. Wood strength, for example,
is different along the grain than perpendicular to the grain.
In the case of cellophane, the refractive index of light, meaning
the amount that light is bent as it passes through the material, is different
in different directions. This makes light polarized in one direction pass
through the cellophane at a different speed than light polarized in the
other direction. "After transmission through such a medium, a phase difference
arises between the two types of light," said Iizuka.
The refractive index and the thickness of the cellophane determine
the amount of the phase difference between the components polarized in the
x and y directions, said Iizuka. The 25 micron thickness used in kitchen
cellophane turns out to make the phase difference 170.2 degrees -- close
enough to the 180 degree phase shift needed to rotate the polarization by
90 degrees. Twenty-five microns is about a third of the thickness of a human
Not only is cellophane available at an extremely low cost, said
Iizuka, it is available in large sheets, making very large three-dimensional
In addition, the necessity of wearing polarized glasses can be eliminated
by replacing them with a large crossed polarizer sheet suspended between
the screen and the observer, said Iizuka. "In other words, let the computer
wear the glasses," he said. This is possible in applications that have only
one viewer at a time, he added.
Iizuka is working on making the technique more suitable for displaying
sign language, he said.
The work appeared in the August, 2003 issue of the Review of Scientific
TRN Categories: Data Representation and Simulation; Applied
Story Type: News
Related Elements: Technical paper, "Using Cellophane to Convert
a Laptop Computer Screen into Three-dimensional Display," Review of Scientific
Instruments, August, 2003.
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