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New concept for a wide-angle collimated display
Article in Proceedings of SPIE - The International Society for Optical Engineering · September 2008
DOI: 10.1117/12.797778
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New concept for a wide-angle collimated display
b
Michel Douceta, Min Wanga, Francis Picard*a, Keith K. Niallb
a
INO, 2740 Einstein street, Sainte-Foy, Québec, Canada, G1P 4S4
DRDC Toronto, 1133 Sheppard Ave. W., PO Box 2000, Toronto, Ontario, Canada, M3M 3B9
ABSTRACT
A unique collimated display concept has been developed by INO and its partners for wide angle immersive display
applications. The concept involves the reflection of scanned beams inside a reflective dome having a symmetry of
revolution and an elliptical profile. The axis of revolution of the reflective dome coincides with the axis of rotation of
the scanning mirror. The nominal position of the observer’s eyes is also located on the reflective dome’s axis of
revolution. The scanning mirror is centered close to one of the foci of the ellipsoidal reflective dome while the eyes of
the observer are located close to the other ellipsoid focus point. The system projects only one line at the time and the full
image is constructed by rotating the image line around the observer by means of the scanning mirror.
Light is generated by a linear array of individually addressable light elements such as a linear array of deformable micromirrors illuminated by a laser line or an array of LED. The beams of light produced by the linear source are conditioned
using specialized optical elements and introduced into the system from the outside by transmission through the dome
shell.
The optical design of such a system is challenging and involves the use of complex optical surfaces. The paper presents
the concept and the original conceptual solutions used to overcome the major design problems.
Keywords: Wide-angle, collimated, display.
1. INTRODUCTION
Flight simulators are used routinely for training in instrument navigation, emergency procedures, refueling, and
operation of electronic systems, and particularly for tasks that are difficult to practice in actual aircraft such as defense
against surface-to-air missiles (SAM) and operations against large enemy forces [1]. Simulators fuse imagery, and
display it immersively in real time. Many flight simulators incorporate conventional rear projection screens, which
produce a more or less Lambertian diffusion, to display real (i.e., uncollimated) imagery. Ocular convergence when
viewing such displays can significantly alter the perception of object size. For example, a companion aircraft simulated
at a given distance appears small compared to a trainee’s memory of the size of such aircraft in actual flight [2]. For
training to be most effective, the imagery must be quickly and accurately displayed with the brightness and crispness of
real life. To exactly simulate out-the window scenes, the display must project images that appear to come from an
effectively infinite distance (i.e., collimated). Collimated display systems are commonly available for wide body aircraft
but their fields of view are limited largely due to the required mechanically positioning of the illuminating projectors.
This paper presents a new concept for a wide field of view collimated display that would be capable of supporting fighter
aircraft training.
2. OVERVIEW OF THE CONCEPT [3]
The realization of a wide angle collimated display is challenging as such a device must produce a large number of
collimated beams coming from a very large range of directions. The realization of such device using conventional
approaches involves large optical components. The display concept presented in this paper discloses a scanning process
which allows the realization of a wide angle display, having collimated display capabilities, with relatively small optical
components .
*
francis.picard@ino.ca; phone (418) 657-7406 ext.510; fax (418) 657-7009; www.ino.ca
Optical Design and Engineering III, edited by Laurent Mazuray, Rolf Wartmann, Andrew Wood,
Jean-Luc Tissot, Jeffrey M. Raynor, Proc. of SPIE Vol. 7100, 710010 · © 2008 SPIE
CCC code: 0277-786X/08/$18 · doi: 10.1117/12.797778
Proc. of SPIE Vol. 7100 710010-1
2008 SPIE Digital Library -- Subscriber Archive Copy
The proposed concept is illustrated on Figure 1. The system displays the image by scanning an image line. The main
components of the wide-angle immersive display system are the reflective dome, the scanner system(s), the linear array
of pixels (LAP) and the shaping module(s).
y
Dome
x
Scanner
z
Shaping module
LAP
Figure 1 : Scheme of the system.
The inner surface of the dome has a reflective coating forming an optical mirror surrounding the observer. The LAP
generates dynamic images consisting of a line of luminous pixels from a linear arrangement of light sources such as a
line of LEDs or an illuminated array of deformable or tilting micro-mirrors. The beams of light produced by the LAP are
conditioned by the shaping module and directed toward the scanner. The scanned beams of light are then reflected
toward the observer by the inner surface of the dome. The final result of the transformation chain is a collimated beam
pointing toward the eyes of the observer for each image pixel of the LAP.
Referring now to Figure 2, only a 1-D series of pixels is displayed at each rotational position of the scanner. This pixel
array would appear to the observer as coming from a portion of a circle located on a spherical surface with infinite
radius. Changing the rotational position of the scanner by a small increment changes the direction of the scanned beams
of light and the system generates another set of collimated beams appearing to come from a 1-D array of pixels located
on a circle portion of the spherical surface adjacent to the previous one. The synchronous addressing of the LAP with the
rotation of the scanner allows the generation of 2D dynamic images appearing to come from an infinite radius virtual
spherical screen.
To ensure the invariance of the optical properties with respect to the rotational position of the scanner, the reflective
inner surface of the dome is a symmetrical surface having an axis of revolution. The axis of revolution of the dome is
coincident with the axis of rotation of the scanner. Moreover, the nominal position of the eyes of the observer is also
located close to the symmetry axis of the dome.
Proc. of SPIE Vol. 7100 710010-2
Infinite radius
virtual spherical
screen
Virtual pixels
y
β
Meridian plan
Meridian
y
Dome
x
α
Collimated beam
Axe of
revolution
Scanner
Beams from
shaping module
z
Observer
Figure 2 : Array of pixels displayed by the system.
3-PROFILE OF THE REFLECTIVE DOME [3]
The profile of the reflective dome is the curve corresponding to the intersection of the reflective surface with a plane
containing the axis of revolution of the dome. The profile should be chosen to perform both the deviation of the beams
towards the eyes of the observer and, in collaboration with the other optical components, the collimation of the beams for
each pixel. General shapes for the profile of the reflective dome have been considered and investigated by means of
simple 2-D models. As shown on Figure 3, the general profile is defined in polar coordinate (r,α) by a truncated Fourier
series :
N
r (α ) = a0 +
∑ [a cos(nα ) + b sin(nα )] , α ε [0,π].
n
n
(1)
n =1
r(α)
α
Figure 3 : Fourier series used to define the profile of the dome.
Optimisation and evaluation of the Fourier profile for the reflective dome has been done by 2-D ray tracing. Specific ray
tracing algorithms have been developed and implemented as a Matlab function. Figure 4 shows a 2-D ray tracing
example for a dome with a profile defined by a Fourier series. The ray tracing is performed in reverse direction starting
from the observer with sets of collimated rays. On figure 4, the observer would be located on the left. The goal of the
process is to find a profile that gives the smallest ray footprint on the scanning mirror to allow the minimisation of the
size of this component. According to the simulations performed, the best results seem to be for elliptic like profiles. An
elliptical profile seems to be a very good choice for the dome since all rays passing through one focal point of an
Proc. of SPIE Vol. 7100 710010-3
ellipsoidal (ellipse of revolution) mirror are reflected toward the other focal point. For an ellipsoidal reflective dome, the
foci are both located on the axis of revolution and the scanner would be centered around one of the foci while the eyes of
the observer would be located around the other focal point.
1800
1600
1400
1200
1000
800
600
400
Axis of
revolution
200
0
Observer
Scanning mirror
-200
-1000
-500
0
500
1000
1500
Figure 4 : 2-D ray tracing on a reflective dome with a profile defined by a Fourier series.
More investigations were done on the particular case of the elliptical profile. The length of the footprint on the scanning
mirror can be estimated with the simple model shown on figure 5. Considering the ray on figure 5 that intercepts the axis
of revolution at point P. This ray intercepts the elliptical profile on point A and its reflected trajectory is determined with
respect to its pilot ray that passes both by the focal point F and point A. The pilot ray is reflected by the elliptic profile
toward the other focus point F `. The trajectory of ray PA is thus determined by the angle γ which it forms with its pilot
ray. Using this simple geometrical consideration, an analytic expression can be derived for the size of the footprint on the
scanning mirror corresponding to each collimated beam propagated in reverse direction from the observer position. The
footprint on the scanning mirror is thus estimated by the superposition of the individual footprints for a sampled set of
collimated beams. The length L required for the scanning mirror corresponds to the length of the superposition of the
footprints of the entire set of beams. This is the sum of the maximum value of the distance GF` with the maximum value
of the distance F`H for the entire set of beams. The value L depends on the shape and size of the ellipse, the diameter of
the beams φ, the total angular field of view ∆α (Difference between the maximum and minimum values of the elevation
angle of view α) and the minimum value of the elevation angle of view αmin. Distance Lc between points F and G is also
an important characteristic that depends on the above-mentioned parameters. Lc is the clearance distance between the
scanning mirror and the observer located near the first focus F.
A
ω ω
γ
P F
φ
α
γ
ň
F`
G
H
Figure 5 : Footprint on the scanning mirror for an elliptical profile.
Simulations were conducted in order to determine the best elliptic profile for the reflective dome. To obtain general
results independent of the scale of the dome, the footprint length L, the clearance distance Lc and the beam diameter
φ were all normalized by the semi-major length a of the ellipse. Figure 6 shows the results for eccentricity values of the
ellipse ranging from 0.1 to 0.5 and for 4 different values of the normalized beam diameter. The leftmost curves
Proc. of SPIE Vol. 7100 710010-4
correspond to the normalized clearance distance while the curves on the right part of the figure correspond to the
normalized scanner footprint length. All curves are for a total angular field of view ∆α of 100o with the minimum value
of the angle of view αmin selected to minimize the footprint length. It seems that the best compromises are for moderate
eccentricity value.
0.8
0.7
5
0.1
0.15
0.2
0.25
φ = 0.15
4.5
0.1
0.15
0.2
0.25
4
0.6
Lc = 0.5
3.5
0.5
3
2.5
0.4
2
0.3
L = 0.5135
1.5
0.2
1
0.1
0
0.05
0.5
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
ε = 0.34
Figure 6 : Normalized footprint length L and clearance distances Lc as a function of the elliptic profile eccentricity ε
for 4 different normalized beam diameters φ . A value of 0.5 has been chosen for the normalized clearance distance.
For a 3 meters long dome, it corresponds to a reasonable clearance distance of 0.75 meter.
3. SCANNING SYSTEM [4]
Figure 4 put the emphasis on an important problem. To obtain collimated beams after reflection on the reflective dome,
the beams must be focalized at points located in between the dome’s inner surface and the axis of revolution at quite
large distances from the scanning mirror. The principal consequence for this is the large footprint on the scanning mirror.
This was pointed out in the previous section in the case of the meridian rays but the problem is even more critical for the
sagittal direction due to the rotation of the scanning mirror. Moreover, the curvature of the reflective dome differs
according to direction. This geometrical anisotropy translates into anisotropic optical power properties. Considering ray
tracing in reverse direction starting from the observer position, the rays from a collimated beam and contained in a
meridian plane (meridian rays as those shown on figure 4) will be focalized by the reflective surface at a distance
different from their counterparts contained in the sagittal plane which is containing the chief ray and is perpendicular to
the meridian plane. The anisotropy problem is less significant in comparison to the first problem mentioned at the
beginning of the paragraph.
Referring to Figure 7, a possible way to address these issues is to encapsulate the reflective surface of the scanner within
a profiled transparent solid cylinder, having a symmetry of revolution about the scanner’s rotation axis. In this case, the
scanner is produced by gluing two separate pieces together. This profiled transparent body acts as a cylindrical lens and
allows a partial compensation for the directional optical power anisotropy of the reflective dome. For a scanner such as
illustrated in Figure 7, the scanning is done by rotating the transparent body itself about its symmetry axis.
Shaft
Transparent material
Figure 7 : General configuration for the scanning mirror.
Proc. of SPIE Vol. 7100 710010-5
Toric shells made of different types of glass or plastic may be added to the transparent body in a concentric configuration
to improve the control of aberrations. Transparent bodies with radial or other distribution of the index of refraction may
also be considered. The exterior and/or interior surfaces of the various layers composing the scanner may be profiled so
as to provide specific corrections. The exterior shells are fixed and only the body that contains the reflective layer has to
be rotated. Figure 8 illustrates the advantages of the embedded scanning mirror. The fixed exterior shell and the rotating
body that contains the mirror layer concentrate the rays toward the center of the scanning device. For large incidence
angle as in the case illustrated on the figure, the extension of the marginal ray would intercept the mirror plane at a
distant point B located at a much larger distance from the rotation axis then the actual interception point A for the
refracted marginal ray. Considering that the rotation speed of the scanning mirror must be around 3600 rotations per
minute (RPM) to produce 60 frames per second, the advantages of the embedded mirror is obvious. Without the
embedded configuration, the large plane surface of the scanner driven at such a rotation speed would be appreciably
deformed in addition of producing a lot of air turbulence and of constituting an important source of danger for the
observer.
B
A
Figure 8 : Ray tracing on an example of the scanning system.
4. BASIC CONFIGURATIONS [4]
For a small clocking angular field of view (defined by angle β in figure 2), the shaping modules can be placed inside of
the dome. However in the case of an immersive display system, the field of view is large and the shaping modules
produce occlusion. To avoid occlusions, all the optics, except the scanner, must be placed outside of the reflective dome.
The beams of light produced by the LAP and transformed by the shaping modules, are introduced in the system by
passing through the dome. The inner surface of the dome is made partially reflective (and thus partially transmissive) to
allow the transmission of the light through its shell. The dome shell is made of a transparent material with its outside
surface covered with absorbing material except at the input ports. The outer surface of the input port can be shaped to
deviate the beams or for aberration correction purposes. The approach of placing the optics outside the dome allows
displaying over a 360o clocking angular field of view since the shaping module(s) are positioned around the scanner in
such a way as to avoid any obscuration.
The difficulties encountered in the correction of the aberrations increase with the angular field of view. A multi-dome
approach is envisioned to improve the optical performances according to the elevation angular field of view (defined by
angle α in Figure 2) by distributing the large field of view over smaller fields. Referring to Figure 9, there is shown an
example of a system having a configuration that includes two domes. In this example, the front dome covers the
elevation angular field of view from 0o to 50o while the back dome covers the 50o to 100o part of the elevation angular
field of view. As it may be observed, the axis of revolution of the second dome is coincident with the axis of revolution
of the first dome. Moreover, in this example, the common axes of revolution are tilted with respect to the horizontal sight
direction of the observer so as to increase forward visibility, i.e. to lessen the forward obscuration caused by the scanner.
Proc. of SPIE Vol. 7100 710010-6
Scanner #2
Dome #1
Scanner #1
Dome #2
Figure 9 : Two-dome configuration.
Splitting the elevation angular field of view over more than one LAP and associated shaping modules can also reduce the
difficulties encountered in the correction of aberrations. A configuration using multiple shaping modules sharing the
elevation angular field of view may be used, each shaping module being shifted both along and angularly around the axis
of revolution of the dome with respect to its predecessor.
Figures 10 shows an example of a system having a configuration that includes two shaping modules which are both
shifted along (Figure 10 a) and angularly around (Figure 10 b) the axis of revolution of the dome. Referring now to
Figure 11, the resulting image from the collimated beams is displayed as two 1-D series of pixels appearing on respective
angularly shifted meridians on an infinite size virtual spherical screen. The entire set of shaping modules with their
associated LAP may be replicated around the axis of revolution of the dome to increase the clocking angular field of
view.
Shaping
module #2
y
Shaping
module #1
Scanner
Dome
x
z
Shaping
module #1
Scanner
Shaping
module #2
z
a)
b)
Figure 10 : Double LAPs configuration.
Proc. of SPIE Vol. 7100 710010-7
Dome
Infinite radius sphere
Virtual pixels from module
#1
y
Virtual pixels from module
#2
β
Meridian plan
#1
y
y
β`
Meridian plan
#2
Dome
Axe of
revolution
Scanner
Collimated beam
Beams from
shaping module #2
Beams from
shaping module #1
x
z
Observer
Figure 11 : Projected image for double LAPs configuration.
5. PRELIMINARY OPTICAL DESIGN FOR THE DISPLAY CONCEPT [5]
Based on this novel concept for the wide-angle collimated display, as described in Section 2, 3, and 4, the preliminary
optical design for this collimated-display system has been carried out. It consists of an ellipsoid dome, an embedded
scanning mirror and a shaping module that includes a beamsplitter. The detailed optical design of the system is given in
this section.
5.1 Reflective dome
As explained in section 2, the reflective inner surface of the dome is a surface of revolution with its axis coincident with
the rotation axis of the scanning mirror. Considering the advantages mentioned in section 3, an elliptical shape with a
semi-major axis of 1500 mm and eccentricity of 0.22 was chosen for the profile of dome. Figure 12 shows the geometry
of the dome. The length b of the semi-minor axis is 1463.16 mm. Note that in that specific case, the scanning system is
located behind the observer.
z
z
Inner surface
y
b
b
Dome
-b
x
Observer
z
Inner surface
a
b
x
Axe of
revolution
Scanner
-y
2a
Figure 12 : Geometry for the dome surfaces.
Proc. of SPIE Vol. 7100 710010-8
The rays are injected inside the dome through the outer and inner surfaces. For simplicity, the outer surface was chosen
in order to have a dome shell with approximately constant thicknesses of 50 mm. The parameters of the outer surface
elliptic profile are 1550 mm and 1513.16 mm respectively for the semi-major and semi-minor axis lengths for an
eccentricity of 0.217.
5.2 Scanning system
In this novel system of collimated display, the scanning mirror is a key component that will carry out the scanning over a
3000 clocking angle of view. This fast moving component will be located within the dome and at a short distance from
the observer. As explained in section 3, the structure of this scan component will not be a simple conventional flat mirror
but a thin reflective film embedded in the middle of a solid rod. A variant of the configuration proposed in section 3 is
considered for this design. It consists of a rod with the thin reflective layer imbedded into two concentric tubes. There is
no air gap in between those components and the components are cemented to produce a solid cylinder. The configuration
is shown on figure 13 with some of its characteristics. Simple cylindrical surfaces (without toric profile) were considered
for this design with the aim of maintaining the manufacturing complexity of the scanning system as low as possible. The
device is made of two different glasses in order to get a better control of the chromatic aberration.
a
-—a
-
236.74 nun
337 •44
C
L
111111
400 nun
560 nun
S-FPL53
S-FPL53
FT]\18
C
Figure 13 : Geometry for the scanning system.
5.3 Aberrated wavefront vs field of elevation
At a first step, before designing the shaping module, it is useful to compute the wavefront aberrations of the sub-system
consisting of the dome and the scanning system. The computation is done by tracing a collimated beam in reverse
direction starting from the eye-box towards the dome where it is reflected by the inner surface in direction of the
scanning system to finally get out of the dome. The reflective layer of the scanning system is not considered in the model
since it introduces only a folding with respect to a symmetry axis. Except for a folding and considering the symmetry of
the system, the optical paths obtained with or without the reflective layer are equivalent. The eye-box diameter Deye box
considered for the calculation is 300 mm and the total elevation field of view is 50 degrees. A Zernike polynomials with
up to 37 terms is fitted to the computed wavefront distortion (optical path difference or OPD). The expression in polar
coordinates for the wavefront distortion W(ρ,θ) is thus given by:
37
W ( ρ ,θ ) =
∑ A Z (ρ ,θ ) ≡ A + A [ρ cosθ ] + A [ρ sinθ ] + .....
i
i
1
2
3
(2)
i =1
where ρ = r/rmax is the radial coordinate r = x 2 + y 2 normalized by rmax, the maximum value taken by r while cosθ = x/r
and sinθ = y/r. The W(ρ,θ) function is expressed in unit of wavelength at 0.56 µm. The computed aberration coefficients
Proc. of SPIE Vol. 7100 710010-9
Ai of the wavefront, which is coming out from the dome, are given in Table 1 for different elevation angles. It is clear
that the off-axis and high-order aberrations increase quickly with the elevation field.
Table 1. Computed main aberration coefficients (unit in wavelength) vs elevation field of view, for
Deye box = 300 nm and λ = 0.56 µm.
Main terms Abb. type
A5
A8
A9
A11
A12
A17
A20
A27
Other high
order
Astig. 3
Coma 3
Sph. 3
Tri. Coma 5
Astig. 5
Qua.Coma7
Astig. 7
F.F.Coma 9
00
8781.7
32
66.1
546.9
233.4
268.3
10.6
25.4
Negligible
Elevation Field of Regard (EFOR)
100
200
300
400
15202.7
22608.8
30064.8
36499
303.5
1097.1
2412.4
3966.6
79.2
76.9
32.2
-63.1
531.8
180.2
-568.6
-1591.2
332.1
462.1
679.1
1033.8
369.2
492
645.7
841.2
8.2
6.3
8.6
8.2
19.3
5.4
-13.95
-41.8
Negligible Negligible A28 = 4.8
A21=20
A28=33.4
500
40843.9
5221.8
-144.4
-2679.7
1540.2
1087.6
-46.4
-124.5
A15=142.8, A21=94,
A28=94
5.4 One-mirror shaping module
It is evident that the field of regard in elevation is severely limited by the off-axis aberrations discussed in the previous
section. The off-axis large aberrations generated by the dome and the scanning system at large elevation angle, especially
high-order aberrations, must be compensated, in order to achieve reasonable image quality. In this design, the large offaxis aberrations are corrected using an off-axis anamorphic mirror. An aspherical shape has been given to the mirror by
adding two-dimensional 16th order polynomial to the surface of the mirror. Additional degrees of freedom were
introduced by allowing decentering and tilting of the mirror as well. A plate beamsplitter (BS) is also used in the design
to eliminate the beam obscuration due to the mirror, as displayed in Figure 14 a). The dimension of the mirror M1 and
the beamsplitter BS on figure 14 a) are respectively 2.2 m x 1.5 m and 1.8 m x 1 m. A 1-D curved line image can be
corrected with this design and a resolution of about 3.2 to 5.6 arcmin can be achieved. This is shown in Figure 14 b), for
a corrected field of elevation of up to 25 degrees. The mathematical description of the shape of the off-axis anamorphic
mirror with bilateral symmetry is given by
Cx x2 + C y y2
z=
1+
1 − (1 + k x )C x2 x 2
− (1 + k y )C y2 y 2
16
+
16
∑a x + ∑b y
i
i
i =1
i
i
(3)
i
where z is the sag of the surface, Cx = 1/Rx and Cy = 1/Ry, are the curvatures in x and y directions, kx and ky, are the conic
constants in x and y while ai and bi, are the aspherical coefficients. The first term in equation (3) corresponds to a biconic
shape.
The well-known commercial optical design software Zemax-EE was used to carry out this design. In practice, all of the
aspherical coefficients, as used to deform the mirrors, have been determined and optimized by the latest version of
Zemax optical code with an actively damped least squares method.
Proc. of SPIE Vol. 7100 710010-10
Ml c mm coo
11.231 .Sm)
Scan-lens
55 II .8o1 ml
3-rn Dome
I.
I
I,
1
CmmcOL
ID I
lioei mesa (Son
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V
CDNFICUEATIDN I DF I
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eyeboo
a)
b)
Figure 14 : a) Ray-tracing in 3D shaded model from the Eye-box to the 1-D image plane, via 3-m ellipsoid dome (made
of Acrylic), scanning system, beamsplitter (in Acrylic), and the mirror (M1) of the shaping module. An eye-box of 300
mm with a corrected field of view of 250 at working waveband of 448 nm to 631 nm was considered. b) Computed RMS
spot radius versus the elevation field of view from 5 to 30 degrees (corrected for 250) in the system. The corrected RMS
spot radius ranges from 3.2 to 5.6 arcmin.
5.5 Two-mirror shaping module
Adding a mirror to the one mirror configuration increases significantly the capabilities of the shaping module. A twomirror configuration allows to generate image with 500 elevation field of view and resolution as good as 2 to 3 arcmin for
a 300 mm eye-box. The main drawback of having such large elevation field of view is the size of the mirrors, which can
be as large as 4.2 m X 1.6 m in the case of the first one in the optical train.
A design consisting of 2 off-axis anamorphic mirrors has been carried out in order to obtain a shaping module with a
large elevation field of view. For this design, aspherical shape has been added by applying two-dimensional 13th order
polynomial corrections to the biconic surfaces of the two mirrors. Additional degrees of freedom were also introduced by
allowing decentering and tilting of the mirrors. A plate beamsplitter is still used in the design to eliminate the beam
obscuration produced by the mirrors. A 1-D curved line image can be corrected with this design and a resolution of about
2 to 3 arcmin was achieved for an elevation field of view of 500. Large elevation field of view seems possible with a twomirror configuration. However, considering the size and costs of the mirrors, multi-projector and multi-dome designs
could provide more efficient solutions as already discussed in section 4.
5.6 Manufacturability of the mirrors
The manufacturing of large mirror is not a trivial task, especially for those with anamorphic aspherical surface. Usually,
the fabrication of aspherics is much more complicated than that of spherical surfaces because of the lack of spherical
symmetry. However, with today’s advanced aspheric-optics manufacturing technologies like single-point diamond
turning, such highly aspherical surfaces would be achievable.
Proc. of SPIE Vol. 7100 710010-11
6. SUMMARY
A new concept for a wide-angle collimated display has been presented. It involves a scanning system, a rotationally
symmetric dome with inner reflective surface and a linear array of pixels ( LAP) with beam shaping optics. The image is
displayed one line at the time and the full image is generated by scanning this line of pixels with synchronous updating.
An ellipse or a shape close to an ellipse have been identified as the most adapted shape for the profile of the reflective
dome. Efficient transfer of the rays from the scanning system toward the observer is achieved by placing the scanning
mirror close to one of the foci of the elliptic profile and the observer eye-box around the other focal point.
To avoid the need of using large scanning mirror, an embedded scanning mirror has been proposed. The proposed system
consists of fixed exterior profiled shells and a rotating body with a thin reflective layer in its middle plane. The interfaces
of the embedded scanning mirror acts as cylindrical lenses that concentrate the rays towards the reflective layer.
Correction of the aberration is also possible with the embedded concept.
The shaping module that shapes the beams of light produced by the linear array of pixels must be located outside the
dome to allow wide-angle capabilities. The beams of light are produced by the LAP, shaped by the shaping module and
inserted into the dome through input ports. A plurality of sets of LAP and shaping modules are distributed around the
dome to cover the desired field of view. A multi-domes approach has also been proposed to extend the elevation field of
view.
Preliminary optical designs have been presented. For a moderate elevation angular field of view (25o), a shaping module
consisting of a single off-axis aspherical mirror was considered. In the case of a large elevation angular field of view
(50o), two off-axis aspherical mirrors are required to correct the aberrations. Large elevation angular field of view
involves large mirrors for the shaping module and approaches with multi-projector and multi-dome seems preferable.
ACKNOWLEDGMENTS
The authors wish to thank Ben Surber (L-3 Communications) and Byron Pierce (Air Force Research Laboratory) for
their help in this project. This work was financially supported by L-3 Communications under contract # PO-TK53596.
REFERENCES
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[3] Doucet, M. and Picard, F. , “Immersive deployable display concept: feasibility study,” INO internal report, 1-59
(2005).
[4] Doucet, M., “Wide angle immersive display system,” Patent document in preparation.
[5] Doucet, M., Wang, M. and Picard, F. , “Immersive deployable display, phase II,” INO internal report, 1-78 (2007).
Proc. of SPIE Vol. 7100 710010-12
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