<s>
Holographic	B-Algorithm
optical	I-Algorithm
element	I-Algorithm
(	O
HOE	O
)	O
is	O
an	O
optical	O
component	O
(	O
mirror	O
,	O
lens	O
,	O
directional	O
diffuser	O
,	O
etc	O
.	O
)	O
</s>
<s>
that	O
produces	O
holographic	B-Algorithm
images	I-Algorithm
using	O
principles	O
of	O
diffraction	O
.	O
</s>
<s>
Early	O
concepts	O
of	O
the	O
holographic	B-Algorithm
optical	I-Algorithm
element	I-Algorithm
can	O
be	O
traced	O
back	O
to	O
the	O
mid-1900s	O
,	O
coinciding	O
closely	O
with	O
the	O
start	O
of	O
holography	B-Algorithm
coined	O
by	O
Dennis	O
Gabor	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
ability	O
of	O
the	O
HOE	O
to	O
allow	O
for	O
transparent	O
displays	O
have	O
caught	O
the	O
attention	O
of	O
the	O
US	O
military	O
in	O
its	O
development	O
of	O
better	O
head-up	B-Application
displays	I-Application
(	O
HUD	B-Application
)	O
which	O
is	O
used	O
to	O
display	O
crucial	O
information	O
for	O
aircraft	O
pilots	O
.	O
</s>
<s>
The	O
holographic	B-Algorithm
optical	I-Algorithm
element	I-Algorithm
is	O
closely	O
linked	O
to	O
holography	B-Algorithm
(	O
science	O
of	O
making	O
holograms	B-Algorithm
)	O
,	O
a	O
term	O
proposed	O
by	O
Dennis	O
Gabor	O
in	O
1948	O
.	O
</s>
<s>
Since	O
the	O
idea	O
of	O
holography	B-Algorithm
came	O
around	O
much	O
has	O
been	O
done	O
over	O
the	O
next	O
few	O
decades	O
to	O
try	O
and	O
create	O
holograms	B-Algorithm
.	O
</s>
<s>
This	O
essentially	O
describes	O
a	O
holographic	B-Algorithm
mirror	O
(	O
one	O
of	O
the	O
first	O
HOEs	O
created	O
)	O
and	O
fixed	O
the	O
issue	O
of	O
overlapping	O
images	O
.	O
</s>
<s>
These	O
two	O
associates	O
encoded	O
and	O
reconstructed	O
images	O
with	O
a	O
two	O
step	O
hologram	B-Algorithm
process	O
on	O
photographic	O
transparency	O
.	O
</s>
<s>
More	O
experiments	O
for	O
holographic	B-Algorithm
instruments	O
such	O
as	O
the	O
holographic	B-Algorithm
stereogram	O
developed	O
by	O
Lloyd	O
Cross	O
in	O
the	O
1970s	O
took	O
the	O
imaging	O
process	O
developed	O
by	O
Leith	O
and	O
Uptanieks	O
and	O
arranged	O
them	O
into	O
vertical	O
strips	O
that	O
were	O
curved	O
into	O
a	O
cylinder	O
.	O
</s>
<s>
A	O
thin	O
HOE	O
(	O
one	O
containing	O
a	O
thin	O
layer	O
of	O
holographic	B-Algorithm
grating	O
)	O
has	O
a	O
low	O
diffraction	O
efficiency	O
,	O
causing	O
light	O
beams	O
to	O
diffract	O
in	O
various	O
directions	O
.	O
</s>
<s>
Conversely	O
,	O
volume	O
HOE	O
types	O
(	O
ones	O
containing	O
multiple	O
layers	O
of	O
holographic	B-Algorithm
gratings	O
)	O
are	O
more	O
efficient	O
since	O
there	O
is	O
more	O
control	O
on	O
the	O
direction	O
of	O
light	O
due	O
to	O
a	O
high	O
diffractive	O
efficiency	O
.	O
</s>
<s>
In	O
the	O
early	O
2000s	O
NASA	O
conducted	O
a	O
test	O
known	O
as	O
the	O
Holographic	B-Algorithm
Airborne	O
Rotating	O
Lidar	O
Instrument	O
Experiment(HARLIE )	O
that	O
utilized	O
dichromate	O
gelatin-based	O
volume	O
HOE	O
sandwiched	O
between	O
float	O
glass	O
.	O
</s>
<s>
The	O
ability	O
of	O
HOE	O
to	O
be	O
made	O
as	O
curved	O
or	O
bendable	O
allows	O
it	O
to	O
be	O
used	O
in	O
the	O
construction	O
of	O
head	O
up	O
displays(HUD )	O
or	O
head	O
mount	O
displays(HMD )	O
.	O
</s>
<s>
This	O
allows	O
for	O
the	O
development	O
of	O
transparent	O
head-up	B-Application
displays	I-Application
that	O
convey	O
information	O
to	O
aircraft	O
pilots	O
and	O
conserves	O
cockpit	O
space	O
.	O
</s>
<s>
One	O
use	O
of	O
a	O
holographic	B-Algorithm
optical	I-Algorithm
element	I-Algorithm
is	O
in	O
thin-profile	O
combiner	O
lenses	O
for	O
optical	B-General_Concept
head-mounted	I-General_Concept
displays	I-General_Concept
.	O
</s>
<s>
A	O
reflective	O
volume	B-Algorithm
hologram	I-Algorithm
is	O
used	O
to	O
extract	O
progressively	O
a	O
collimated	O
image	O
that	O
was	O
directed	O
via	O
total	O
internal	O
reflection	O
in	O
an	O
optical	O
waveguide	O
.	O
</s>
<s>
The	O
spectral	O
and	O
angular	O
Bragg	O
selectivity	O
of	O
the	O
reflective	O
volume	B-Algorithm
hologram	I-Algorithm
makes	O
it	O
particularly	O
well-suited	O
for	O
a	O
combiner	O
using	O
such	O
light	O
sources	O
as	O
RGB	O
LEDs	O
,	O
providing	O
both	O
good	O
see-through	O
quality	O
and	O
good	O
quality	O
of	O
the	O
projected	O
image	O
.	O
</s>
<s>
This	O
usage	O
has	O
been	O
implemented	O
in	O
smart	B-General_Concept
glasses	I-General_Concept
by	O
Konica	O
Minolta	O
and	O
Sony	O
.	O
</s>
<s>
One	O
of	O
the	O
goals	O
in	O
the	O
design	O
of	O
an	O
HOE	O
is	O
to	O
try	O
and	O
create	O
3D	O
visualization	O
and	O
the	O
closest	O
thing	O
to	O
that	O
is	O
augmented	B-General_Concept
reality	I-General_Concept
.	O
</s>
<s>
The	O
most	O
common	O
types	O
of	O
augmented	B-General_Concept
reality	I-General_Concept
come	O
from	O
head	B-General_Concept
mount	I-General_Concept
displays	I-General_Concept
or	O
glasses	O
type	O
displays	O
,	O
which	O
can	O
be	O
considered	O
the	O
first	O
type	O
of	O
3D	O
displays	O
.	O
</s>
<s>
The	O
coupled-wave	B-Algorithm
theory	I-Algorithm
is	O
a	O
crucial	O
part	O
of	O
the	O
design	O
of	O
volume	O
HOEs	O
.	O
</s>
<s>
These	O
equations	O
are	O
used	O
to	O
adjust	O
the	O
hologram	B-Algorithm
grating	O
volume	O
and	O
increase	O
the	O
diffraction	O
efficiency	O
of	O
the	O
HOE	O
during	O
production	O
and	O
can	O
be	O
applied	O
to	O
both	O
transmission	O
type	O
HOEs	O
or	O
reflection	O
type	O
HOEs	O
.	O
</s>
