Progress on waveguide-based holographic video
(Invited Paper)
S. McLaughlin
1
, C. Leach
1
, S. Gneiting
1
, V. M. Bove, Jr.
2
, S. Jolly
2
, and D. E. Smalley
2,
*
1
Electroholography Group, Brigham Young University, 459 Clyde Building, Provo, Utah 84602, USA
2
MIT Media Laboratory, Massachusetts Institute of Technology, 77 Mass. Ave, Cambridge, Massachusetts 02139, USA
*Corresponding author: smalley@byu.edu
Received September 18, 2015; accepted November 26, 2015; posted online January 25, 2016
This paper presents progress on the characterization of guided-wave light modulators for use in a low-cost
holographic video monitor based on the MIT scanned-aperture architecture. A custom-built characterization
apparatus was used to study device bandwidth, RGB operation, and linearity in an effort to identify optimal
parameters for high bandwidth, GPU-driven, full-color holographic display.
OCIS codes: 090.1705, 090.1970, 090.2870, 090.2890, 090.5694.
doi: 10.3788/COL201614.010003.
Scanned aperture technology was first introduced as a sol-
ution for holographic video by the Spatial Imaging Group
at the Massachusetts Institute of Technology (MIT)
[1]
.
The MIT architecture uses an acousto-optic modulator
(AOM) to create holographic patterns made of acoustic
waveforms. As shown in Fig.
1(a), the AOM is imaged
through a telescope to demagnify the acoustic waveform.
The resulting image has a small apparent lateral extent
but a larger angular sweep. A rotating mirror is placed
at the Fourier plane of the telescope, which descans the
aperture of the AOM to make the travelling acoustic pat-
tern appear stationary and to greatly increase the lateral
extent of the display output. This architecture is scaled by
adding AOM channels, which increases the overall display
bandwidth
[2]
. Once this is done, the bandwidth can be used
to achieve the design parameters of the telescope and the
scanning mirror. Furthermore, the display can employ this
available bandwidth to increase the display output angle,
frame rate, image extent, and vertical resolution
[3]
. The
first two scanned aperture holographic video prototypes
were limited in their reproducibility due to the cost of
the optical and computational components as well as
by the limited bandwidth available from commercial tel-
lurium dioxide Bragg cell AOMs. In his Ph.D. thesis,
Dr. St-Hilaire suggested several improvements to reduce
cost and increase bandwidth, which included replacing
the large doublet output lens with a reflective optic and
replacing the tellurium dioxide modulator with a lithium
niobate modulator, which has a lower acoustic attenua-
tion and is capable of higher bandwidths than the former.
It was assumed, correctly, that the rapid increase in com-
putational power would eventually obviate the need for a
costly custom-drive computer
[4]
.
The supercomputer used to run the original prototypes
was replaced by Bove et al. by a commodity computer uti-
lizing multiple high-end graphics cards
[5,6]
. Later, many of
the expensive optical components, such as the output lens,
were replaced with less expensive optics
[3]
. The optical
path was folded to create a display with a monitor-like
form factor [see Fig.
1(b)]. The new monitor design was
built to include three decks that are folded from water
jet cut pieces of aluminum (alloy 5250). The entire optical
assembly was made to slide in and out of the display to
make it easier to repair and modify the display ’s optics.
The output lens was replaced with a parabolic reflector,
rather than a refractive lens. In this way, one is able to
construct output optics with smaller f-numbers. This
higher numerical aperture at the output enables the focal
lengths of the telescope to be shortened while maintaining
the total system magnification. This results in a reduced
Fourier plane that enables the use of polygons with both
fewer and smaller facets.
Smalley and colleagues also created a custom guided-
wave modulator, fabricated on a lithium niobate sub-
strate, to replace the tellurium dioxide Bragg cell [see
Fig. 1. (a) Scanned aperture holographic video architecture.
(b) Holographic video monitors under construction at Brigham
Young University.
COL 14(1), 010003(2016) CHINESE OPTICS LETTERS January 10, 2016
1671-7694/2016/010003(5) 010003-1 © 2016 Chinese Optics Letters
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