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DW2A.20.pdf Digital Holography and 3D Imaging 2015
A combination of computer-generated Fourier holograms
and light guide substrate with diffractive optical elements
for optical display and sighting system
A.Yu. Betin1, S.S. Dontchenko1, M.S. Kovalev1, S.B. Odinokov1, A.B. Solomashenko1**, E.Yu. Zlokazov1,2*
1 Bauman Moscow State Technical University, 105005, 2nd Baumanskaya str. 5, Moscow,Russia
2 National Research Nuclear University “MEPhI”, 115409, Kashirskoe str. 31, Moscow,Russia
e-mail: *ezlokazov@gmail.com, **art_s87@mail.ru
Abstract.A combination of computer-generated Fourier holograms (CGFHs) and light guide
substrate with diffractive optical elements (DOEs) is described. The experimental results show
that this combination can be used in display and sighting systems.
OCIS codes:(090.2890) Holographic optical elements; (050.0050) Diffraction and gratings
1. Introduction
Currently, DOEs with light guide substrates are used in miniature display systems [1-4] especially in systems for
vehicles, aircraft, and systems, where the observed image overlaps with the real scene. The use of DOEs reduces the
longitudinal dimensions of the optical display and sighting systems due to the effect of total internal reflection
(TIR) of light in the glass substrate [1-4]. The application of such structures, combined with computer-generated
Fourier holograms, in aiming and targeting systems will also provide a number of advantages. For example, with
these combined elements, the weight and size of sighting systems can be significantly reduced; brightness of central
aiming point, determined by zero diffraction order is significantly higher than the other parts of the sighting mark;
this configuration allows you to quickly change the type of the aiming mark depending on the shooting conditions.
2. A combination of CGFH and DOEfor optical display and sighting scheme
A combination of CGFH and light guide substrate with DOE for optical display and sighting system is show in
Fig. 1. This configuration consists of glass substrate with CGFHs and diffraction gratings (DGs), as a DOE, for
input and output of radiation.
Reconstructing beam is incident on the CGFH, and then through DG 1 radiation is introduced into the plate at
an angle of TIR and spread in it. When the light reaches the surface of the substrate with a DG 2, part of the light
emerges from it. DGs are two diffraction gratings [1,3], which should have different diffraction to ensure uniform
brightness of the observed image. It should be noted that to ensure the non-uniform diffraction efficiency of DG
exit area was divided into multiple zones. Thus, the zonal DG was recorded with its exposure value [5].
Light beams diffracted on CGFH enter and then multiple output from substrate, thus forming for observer an
increased image of the test object.
Fig. 1.Schematic representation of combination of CGFHs and light guide substrate with DOEs
DW2A.20.pdf Digital Holography and 3D Imaging 2015
Reconstructed field consists of three spatially separated regions consisting of δ-functions in the central (zero)
order and two conjugate images of the object at ± 1 diffraction orders. Fig. 2 shows the synthesized Fourier
hologram and the object numerically reconstructed from this CSFH. Thus, the zero diffraction order, observed as
the central point of the image, can perform the aiming point function for sighting and targeting systems, and the
image, which is reconstructed by CSFH, is "framed" its. Moreover, additional information is projected in the field
of view of the operator by CSFH.
Such structure can be a basic element of holographic sight, holographic signs-symbolic information indicator,
and other displays, which can be mounted directly on the head of pilots, soldiers, vehicle riders, etc.
(a) (b)
Fig. 2. (a) CSFG of test object as grayscale bitmap image; (b) test object, numerically reconstructed using this CSFH
The synthesis algorithm of CGFH is based on operation of two-dimensional fast Fourier transform. Synthesized
hologram can be represented as grayscale bitmap image, as shown in Fig. 2(a), and displayed in optical recording
scheme by the use of high-resolution spatial light modulator [6].
While reconstruction of CGFH encoded data object requires similar coherent optical scheme as in the case of
classical two-beam Fourier holography method, the projection recording scheme appears to be simpler since it does
not require two laser beams precise cross-sectioning and can be built on the base of both coherent and incoherent
monochromatic light sources [6,7].
3. Experimental study for using CGFH
To confirm the performance of the proposed scheme experimental samples of CGFHs and DGs with variable
diffraction efficiency on dichromated gelatin were obtained, as this material is sufficiently transparent.
In this case on the same substrate was recorded just two CGFHs of different test objects. Dimensions of
CGFHs are rectangles with about 4 mm in width and 20 mm length. When moving the plate within the
reconstructing beam different images of test objects were observed using the light guide plate, as shown in Fig. 3.
Fig. 3.Different images of test objects outputted using suggested combined structure
The reconstruction scheme is shown in Fig. 4. In this case, the light guide substrate and CGFH were recorded
on different substrates connected to each other.
DW2A.20.pdf Digital Holography and 3D Imaging 2015
Fig.4.The experimental sample and the CGFH reconstruction scheme
Subsequently, the CGFH at the entrance of light guide can be replaced by LCD or OLED display. Thus it is
possible to dynamically change the display information and to use this scheme at the display systems and sign-
symbolic information indicators. However this issue requires additional consideration.
4. Conclusion
The combination of computer-generated Fourier holograms and light guide substrate with diffractive optical
elements has been explored. Different types of test objects were reconstructed using this configuration and the
ability to quickly change the displayed object was provided by changing the type of CGFH placed in reconstructing
beam. The experimental results represented in this paper showed that light guide substrates with diffraction gratings
and CGFH can be used in sighting and display system, that allows to significantly reduce the size and weight of
these systems. It should be noted, that the disadvantage of use a CGFH is a presence zero diffraction order, which
will be observed in the field of view.
Acknowledgments
The research was carried out at BMSTU. This work was supported by a grant # 14.574.21.0066 (Project ID
RFMEFI57414X0066) and by a grant of the main part of the state order "Organization of scientific research" and
"Providing of scientific research" from the Ministry of Education and Science of the Russian Federation.
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