[Citation] International Display Workshop 2023 (IDW'23): 3D Systems and Applications 2023 (3DSA2023), Niigata,
paper 3DSAp1-5, 1313-1316 (2023.12.7).

Increase in size of full-color stacked CGVH
by tiling contact-copy
Shunsuke Fujiki1, Hirohito Nishi1, Kyoji Matsushima1
k524366@kansai-u.ac.jp (S. Fujiki)
1Department of Electrical, Electronic and Information Engineering, Kansai University,

3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan
Keywords: CGH, computer-generated volume hologram, transfer hologram
ABSTRACT
A novel technique is presented for increasing in the sizeof stacked CGVHs (computer-generated volumehologram) that reconstruct high-quality full-color fullparallax 3D images. A tiling technique is introduced toextend the size without increasing the laser power usedfor contact-copy.
1

Introduction
Computer-generated holograms (CGH) commonlyreconstruct monochrome images unless special opticalsetup is used. Full-parallax high-definition CGHs (FPHDCGH) calculated by the polygon-based method andsilhouette method are printed using laser lithography andreconstruct monochrome images of amazing deep 3D
scenes with natural motion parallax and no sensational
conflicts [1,2]. For the FPHD-CGHs, two practical methods
have been proposed for full-color reconstruction: themethods using RGB color filters [3] and stacked CGVH
(computer-generated volume hologram) [4].
In the RGB color filters method, large FPHD-CGHs
whose size is 18cm × 18cm have been created [5], but an
RGB laser is necessary to reconstruct clear 3D images
because of the broadband property of the RGB color filters.
In addition, the reconstructed full-color images are
deteriorated in quality because of splitting the fringepattern. On the other hands, the stacked CGVH featuresbrighter and less noisy full-color 3D images. Furthermore,
the quality images are obtained by illumination using awhite LED; we do not need any laser light source. However,the size of quality full-color CGVHs was limited toapproximately 5cm × 5cm. This is mainly because theoutput power of the laser used for fabricating CGVH islimited to hundreds mW due to the workers safety.
Although a beam-scan technique was attempted toincrease the size of stacked CGVHs, degradation isreported in the image quality [6]In this paper, we proposed a novel method to increase
the size of full-color stacked CGVHs by employing a low
power laser and the technique referred to as tiling contactcopy. Not only a presentation on the technique but also
actual full-color stacked CGVHs will be exhibited in theposter or exhibition room.

2Principle of tiling contact-copy

2.1 Contact-copy
The contact-copy is a method to transfer an original
printed CGH to volume holograms and produce CGVHs.
As shown in Fig. 1, the original CGH and a sheet ofphotopolymer, attached in contact with the original CGH,
are illuminated with monochromatic light referred to astransfer light. Here, the transfer light is the same light as
the reference wave used for calculating the original CGH.
The transfer light illuminates the original CGH throughthe photopolymer and reconstructs 3D images of theoriginal CGH that is a reflection hologram because of themetallic fringe printed by laser lithography. The light ofthe 3D image works as an object wave and interfereswith the transfer light itself.
The fringe recorded in the photopolymer has a 3Dstructure because the object wave and transfer lightenter the photopolymer in the opposite direction.
Accordingly, a CGVH copying the 3D image of theoriginal CGH is formed in the photopolymer. This CGVH

Original CGH

Photopolymer

Reconstructed
image

Monochromaticlight

Fig.1 The principle of the contact-copy

CGVH

Green CGVH

Red CGVH

Combined

Full-color image

White lightBlue CGVH

Substrate
Fig.2 The principle of full-color reconstruction.

Substrate
DM: Dichroic mirror
Aperture Shutter
DM DM

Photopolymer

Spatial filter

Aperture
Collimator lensOriginal CGH

Fig.3 The principle of tiling contact-copy

2.3 Tiling contact-copy
In the contact-copy, a certain level of optical intensity isrequired for the transfer light to form a CGVH in thephotopolymer. Because optical intensity of the transfer
light is reduced with increasing the area of the contactcopy, a high power laser must be introduced to achieve
expansion of the CGVH.
To avoid the problem, we introduced a novel technique,called tiling contact-copy, for extending the size of CGVHs.
In this technique, as shown in Fig.3, a part of the original
CGH and photopolymer is illuminated by the squarecollimated transfer light. The original CGH andphotopolymer are installed on an automatic stage to movethe area of contact-copy. By repeating the process until
filling the whole area of the original CGH, we can fabricate
a large CGVH. After fabricating three large CGVHs in RGB
colors, the CGVHs are stacked with accurate alignment toreconstruct full-color images, as mentioned in the previoussection.
3

Fabrication of large stacked CGVH
We attempted to produce a full-color stacked CGVH
over 10cm by tiling contact-copy. Figure 4 shows theoptical setup for tiling contact-copy in three colors. Thesize of the rectangular aperture is 26.2 mm × 26.2 mm.
The outputs of three lasers whose wavelength isMirror

Table 1 Parameters of the original CGHs.
Number of pixels
Pixel pitches [μm]Wavelengths [nm] (R, G, B)
Number of polygons

131,072 × 262,144
0.8 × 0.4
(640,532,457)
5,292

200

105

2.2 Full-color reconstruction by stacking CGVHs
When illuminating a CGVH with a white light, the CGVH
reconstructs the 3D image by reflection at the samewavelength as that of the transfer light. Therefore, as
shown in Fig.2, by stacking three CGVHs fabricated atthree wavelengths corresponding to R, G and B primarycolors, we can obtain a full-color image by integration ofRGB monochrome images [4]. Here, note that the original
CGH must be calculated with compensation for thicknessof the CGVH substrates to superpose RGB color images
exactly.

532[nm]Fig.4 Optical setup for tiling contact-copy atthree wavelengths.

Laser beam
can reconstruct high-quality monochromatic image byreflection of illumination light. Here, note that a broadband
light source such as a white LED can be used forillumination because of the property of wavelength
selectivity inherited from volume holograms.

457[nm]Collimator lens Mirror
Photopolymer

Spatial filter

Lasers640[nm]105

Original CGH

105
105

Units: mm

Fig.5 3D scene used for calculating the originalCGHs.
corresponding to primary colors are superposed in a
coaxial beam using dichroic mirrors (DM). Note that only
one laser is turned on to fabricate a single CGVH and thelaser is switched after completing the single CGVH.
We actually created a large stacked CGVH using theproposed technique. The 3D scene and parameters ofthe original CGHs are shown in Fig. 5 and Table 1,respectively. The original CGHs for each color arecomposed of approximately 17 billion pixels. The CGVHs
whose size is 105mm × 105mm are fabricated by 4 × 4
tiling contact-copy of the original CGHs. Time of tilingcontact-copy was less than 15 min for each CGVH.
Table 2 summarizes the parameters of the tiling contactcopy.
4

Optical reconstruction and discussion

4.1 Optical reconstruction of stacked CGVH
Figure 6 shows optical reconstruction of the fabricatedstacked CGVH. The illumination light source is a white
LED with fiber output. It is verified that a high-quality fullcolor 3D image is reconstructed by the white illumination
when staring the reconstructed 3D images. However, as
shown in Fig.7, when focusing on the surface of thestacked CGVH, the boundaries between tiles arenoticeable.

4.2 Discussion on boundaries
The boundaries between tiles seem to be thicker thanthat we expected from the accuracy of the automatic stageused. In addition, thickness of the boundaries of upper tiles
tends to be larger than that of lower tiles as shown in Fig.7.
Figure 8(a) shows layered structure of the original
printed CGH whose fringe pattern is generated bynumerical interference by a spherical reference wave.
Here, the center of the spherical wave is placed under theCGH. The recorded wave of the CGH is exactly
reconstructed when the same spherical wave as thereference wave illuminates the CGH. However, in the tilingcontact-copy, a collimated transfer light entersperpendicularly to the photopolymer and original CGH, asshown in Fig. 8(b). As a result, the photopolymer records
reconstruction light of the original CGH with a carrier offset.
When the same spherical wave as the reference wave
illuminates the photopolymer, the carrier offset is canceled
and the 3D images of the original CGH is reconstructed in
the proper direction.
However, when copying the tile 1 in tiling contact-copy
as in Fig. 8(b), at the edge of the tile, light of the original
CGH reaches photopolymer of the neighboring tile 2. But
the photopolymer does not record the light because there
is no transfer light in the tile 2. As a result, lightreconstructed by the original CGH is not recorded on

Leftphotopolymer at the edge of the tile. This is most likely
the reason that boundaries are much noticeable.
This problem can be relieved by changing the order oflayers so that photopolymer directly contacts with thefringe, as shown in Fig. 8(c). Figure 9 shows
photographs of boundaries in green CGVHs. It is verified
that the boundaries in (a) are more noticeable than thatin (b) where photopolymer directly contacts with thereflection fringe as in Fig. 8(c). However, in this case,another noise is caused by interference of backside
surface reflection of the glass substrate. This effect ismost likely avoided by anti-reflection coating or using aphase-only reflection CGH for the original CGH [7].
5Conclusions
We have successfully fabricated high-quality full-color
stacked CGVH exceeding 10 cm in the size by using theTable 2 Parameters of tiling contact-copy.
Wavelength [nm]Exposure [mJ/cm2 ]Exposure time [s]Number of tiles
Size [mm]Settling time [s]Photopolymer

CenterRed
640
2.18GreenBlue
532
457
1.4
0.6
3030
4×4
26.2 × 26.2
15
Bayfol🄬HX200Right

Fig.6 Photographs of optical reconstruction of the stacked CGVH fabricated by tiling contactcopy. The camera is focused on the reconstructed 3D image.

LeftCenterRight

Fig.7 Photographs of the stacked CGVH. The camera is focused on the surface of the CGVH.

proposed tiling contact-copy. It is verified
that a high-quality full-color 3D image isreconstructedbywhiteillumination.
However, boundaries between tiles areslightly detected. We discussed on thecause and suggested a method forimprovement.
This work was supported by Japan
Society for the Promotion of Science (JSPS)
KAKENHI 22H03712 and the commissioned
research (No. 06801) by National Institute ofInformation
andCommunications
Technology (NICT), Japan.

Referencewave
Glasssubstrate

Original
CGH
Tile 1(a)Transferlight

Tile 2

Reflection
fringePhotopolymer
Glass
substrate

Original
CGH
Tile 1(b)Tile 2

Reflection
fringePhotopolymer
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Fig.9 Photographs of boundaries of CGVHs. Photopolymer does not directly contact with thereflection fringe in (a), while it directly contacts with the fringe in (b).