age to a volume the size of a ping-pong
ball, and the results demonstrated so
far are based on long-exposure images
that took up to a minute to generate.
Says Barry Blundell, senior lecturer
in computing at the University of Derby
in the U.K. and a researcher into volumetric displays since the late 1980s,
“With the optical-trap display, I would
have to see images generated a lot
faster. The only way to do that is parallelism; you’ve got to have more lasers
surrounding the display, and more particles. The problem could be that you
need to have so much physical apparatus that you lose the viewing freedom.”
Smalley claims the technology exists to drive and illuminate a collection
of particles in the shape of the spatial
light modulator, the same kind of device as that used to research holographic displays and optical computers. Bove
argues the laser and light-modulator
components needed for scaled-up displays are now relatively cheap.
Still, expectations may be set too high.
“The general public has for 40 years
been seeing cinematic depictions
of physically impossible things, and
when they do see what’s possible, they
are disappointed,” says Bove.
Smalley concedes, “At this stage, you
don’t have to be an expert to realize that
this isn’t the Princess Leia display you
are looking for. But, if given the oppor-
tunity to be developed further, I don’t
think you would be disappointed.”
Researchers may be trying too hard
to make fact out of fiction. “What some
of the people working on volumetrics
haven’t realized is that the key ele-
best material. It seems unlikely that it
is,” he says.
It is possible to produce freestanding volumetric images without injecting particles into the air. More than a
decade ago, Hidei Kimura, founder
and CEO of Japanese company Burton Inc., and Taro Uchiyama of Keio
University found that when focused
on specific points, microsecond bursts
of high-intensity infrared light could
cause air molecules to become glowing plasma. Kimura envisaged the
technology being used to create levitating signs above head height for use
in emergencies; the bursts would be
intense enough to burn the hand of a
user foolish enough to try to touch the
glowing voxels.
Much shorter pulses could yield a
safer system. Yoichi Ochiai of the University of Tsukuba and Kota Kumagai
of the University of Utsunomiya in Japan showed at the ACM SIGGRAPH
conference in 2015 the results of a prototype based on lasers that fire bursts
no more than 100 femtoseconds long.
According to Ochiai, users would
simply get a tingling sensation from
touching the plasma voxels, though
users would need to be careful to not
let their eyes get too close to the images, as retinal damage is a distinct
possibility. Robert Stone, professor of
interactive multimedia systems at the
University of Birmingham in the U.K.,
says he has concerns over the eye forming strong afterimages because of the
brightness of the plasma.
The plasma projector has the advantage of being far more resistant to
disturbance by moving hands than
the particle-based option. However,
all volumetric displays to date have a
common problem, Smalley says: “It
is like taking a bunch of fireflies and
organizing them into patterns. Everything looks like a ghost. You don’t have
the self-occlusion to make objects that
look realistic.
“We want to be able to take a point
and have it shine light in only one di-
rection. That would mean it begins to
look solid.”
The lack of self-occlusion in the op-
tical-trap display is, for the moment, a
secondary issue. It is difficult to move
the single particle that flies around the
Brigham Young display any faster than
is possible today; that limits its cover-
“The general public
has for 40 years
been seeing
cinematic depictions
of physically
impossible things,
and when they do
see what’s possible,
they’re disappointed.”
ments are complex movement and dynamics, not super-high resolution,”
Blundell argues.
Smalley envisages applications
where the user needs to inspect the
shape closely and move around it. The
ability to produce mid-air streamers in
fluid-dynamics simulations and models
of organs to help with planning medical operations seem good examples.
“A lot of 3D technologies can’t give you
a strong spatial sense when you get up
close. With ours, you can,” he says.
Bove says by looking closely at requirements for target applications
and working with user-interface designers, the developers of volumetric
displays can move from experiment to
market more easily. “Can it be behind
a transparent barrier? Is it important
that it be viewable from any angle or
is 90 degrees OK? Is it acceptable for it
to have moving parts?” he suggests as
questions to be asked.
Developing volumetric technologies for specific applications may lead
to the problem of no individual market
being large enough to support research
and development, but such displays
look more technologically feasible,
Bove says. “The problem with the Leia
display is that it needs all of the boxes
to be ticked.”
Further Reading
Smalley, D.E. et al
A Photophoretic-Trap Volumetric Display,
Nature, 553, pp486–490 ( 25 January 2018),
doi: 10.1038/nature25176
Ochiai, Y., Kumagai, K., Hoshi, T., Rekimoto, J.,
Hasegawa, S., and Hayasaki, Y.
Fairy Lights in Femtoseconds: Aerial and
Volumetric Graphics Rendered by Focused
Femtosecond Laser Combined with
Computational Holographic Fields, ACM
Transactions on Graphics, Volume 35, Issue
2, (May 2016), doi: 10.1145/2850414
Blundell, B.
On the Uncertain Future of the Volumetric
3D Display Paradigm, 3D Research, 8 ( 2)
p11, doi: 10.1007/s13319-017-0122-2
Joseph, D.M., Smoot, L.S.,
Smithwick, Q. Y., and Ilardi, M.J.
Retroreflector Display System for
Generating Floating Image Effects, U.S.
Patent Application 2018/0024373 A1 ( 25
January 2018)
Chris Edwards is a Surrey, U.K.-based writer who reports
on electronics, IT, and synthetic biology
© 2018 ACM 0001-0782/18/10 $15.00