M4B.1.pdf

Digital Holography and 3-D Imaging 2017 © OSA 2017

Application of wavefront printer-from static 3D visualization to projection-type
holographic displayKoki Wakunami*1
1

National Institute of Information and Communications Technology,*
k.wakunami@nict.go.jp

Abstract: Wavefront printer can record arbitrary designed wavefront not
only for static 3D visualization but also for holographic screen to be used on
projection-type holographic display. Some applications related to thewavefront printer are introduced.
OCIS codes: (090.0090) Holography; (090.1760) Computer holography; (090.2870)
Holographic displays.

1. Introduction
For hologram recording of digital three-dimensional (3D) data, wavefront printer has been
proposed by several research groups [1-4]. In contrast to a holographic stereogram (HS)printer that is based on the recording/reconstruction of dense light-rays, wavefront printerrecords the wavefront with full-control of both amplitude and phase distributions reproducedby computer generated holograms (CGH). Therefore the expected application of wavefront
printer is not only 3D data visualization but also the fabrication of holographic optical element(HOE) implemented with a digitally designed arbitrary optical function. In this paper the basic
principle of wavefront printer is introduced and then the some applications; recording ofreal/virtual 3D data for visualization, fabrication of HOE as a holographic screen used on
projection-type holographic 3D display are reported.
2. Principle of wavefront printerIn pre-processing of wavefront printing, an arbitrary wavefront to be recorded is transformed
to a CGH and then it is divided into a set of sub-CGH if the pixel number of spatial light
modulator (SLM), which is used in wavefront printer, is not enough to display an original
CGH.
@532nmPBS

HWP

Reference beamMLASER
x-y stage

Object beam
HWP: half wave plate
PBS: polarizing beam splitter
SSBF: single-side band filter
SLM: spatial light modulator
SF: spatial filter
M: mirror

PBS

SSBFSFMSLM

Hologram Recording materialFig.1 Optical setup
Fig.1 shows the optical system of our wavefront printer. In A collimated light at 532 nm ofwavelength is split by polarization beam splitter (PBS) and then, two beams will form anobject beam and a reference beam to record a sub-hologram as a reflection-type volumehologram. Sub-CGH is displayed on SLM and the reproduced wavefront passing through thereduction optical system is sequentially recorded as a sub-hologram at the given region intilling manner to form an entire hologram by using a motorized X-Y stage. Cobestro
Bayfol®HX-102 photopolymer film is used as a hologram recording material. After theM4B.1.pdf

Digital Holography and 3-D Imaging 2017 © OSA 2017

recording of all sub-holograms, holographic recording material is then processed by thebleaching so as to own high transmission at visible light wavelength.
3. Recording 3D data of real/virtual objects
To confirm the potential of wavefront printer for 3D data visualization, 3D data of both realand virtual objects were recorded. CGHs of the real object: the miniature stature of “Buddha”,
and the virtual object: 3DCG (3D computer graphics) data “Venus”, were calculated based on
the holographic stereogram (HS) based approach from 544 × 544 of perspective images at 512
× 512 pixels rendered by CG rendering software. In the case of “Buddha”, 47 of multi-view
images were taken from random positions by the camera and then the pictures were combinedto generate 3D CG data on the software “123D catch” [5] to render a set of perspective images.
The hologram size was set 10 × 10 cm and the total pixel number of CGHs were 278,528 ×
278,528 pixels. All of CGH calculation processes from a set of perspective images wereexecuted on the supercomputer TSUBAME2.5 provided by GSIC center in Tokyo Institute ofTechnology [6]. CGHs were then divided into 155 × 155 of sub-hologram data at 3,600 ×
1,800 pixel considered with overlapping recording condition [4].
Fig.2 shows the original 3D data “Venus”, “Buddha” and the results of optical reconstruction.
Both 3D contents were successfully recorded into the holograms. Since the recorded
holograms have the wavelength selectivity as a principle of reflection-type volume hologram,the white illumination light source could be used for the optical reconstruction.

(a) Virtual object(b) Real object

Fig.2 Application of 3D data visualization
4. Fabrication of holographic screen for projection-type holographic 3D display
DDHOE (digitally designed holographic optical element), which is an HOE fabricated byusing the wavefront printing technique, has several advantages compared with the generaldiffractive optical element/HOEs, for example, the freedom of implemented optical functions,the ease of fabricating large HOEs, good transparency due to its wavelength selectivity. In thissection, the application example of DDHOE fabricated to be used as a holographic screen on
projection-type holographic 3D display is introduced. Generally holographic 3D displays havethe inherent trade-off between two parameters: the display size and the visual angle to viewthe entire display area, due to the severe limitation of the spatial-temporal resolution ofcurrent SLM for holographic 3D display use. From the viewpoint of the practical use,
however, freely design of both parameters is important to allow wide application fields suchas digital signage, in-car head-up displays, smart-glasses and head-mounted displays. To
overcome the trade-off between the display size and the visual angle, the projection-type
holographic 3D display in which the DDHOE of holographic screen is used as a see-throughscreen of holographic projection technique. In this approach, the digital holographic projector
magnifies the holographic image on the DDHOE screen. This holographic image is thenreflected to the target observation point by the implemented optical function of DDHOEscreen. From the center of projection at (0, 0, zP) to the target observation point at (xO, yO, zO),
the phase distribution implemented on the DDHOE screen is defined as

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Digital Holography and 3-D Imaging 2017 © OSA 2017(1)
where the origin of XYZ coordinate was set at the center of DDHOE screen, d = zOzP/(zO + zP),ξ and η are(2)In this time, the center of projection and the target observation point were set at (0 mm, 0 mm,1,000 mm) and (0 mm, 59 mm, 200 mm), respectively. Fig. 3 shows the visualization of the
optical function of the fabricated DDHOE screen. In the artificial fog, the spherical wave,
which is supposed to the holographic projection light, propagated from (0 mm, 0 mm, 1,000mm) to the DDHOE screen, then the incident light was reflected to be focused at the target
observation point [see Fig.3 (a)].

Target observing point(b) Original 3D dataDDHOE screen(a) Optical function of DDHOE screen(c) Optical reconstruction

Fig.3 Optical function of DDHOE screen and the optical reconstruction of projectiontype holographic 3D display
Fig.3 (b) shows the original 3D data to be displayed in the experiment. The CGH data of thiscontent was calculated based on HS approach. The holographic projector had 8K (7,680 ×4,320 pixels) SLM at 4.8 μm of pixel period. The optically reconstructed wavefront of theCGH was then projected on the DDHOE screen by the projection lens at 1,500 mm of thefocal length. The magnification ratio was set 2.0 and so the display size became 75.4 × 41.4
mm2. Fig.3 (c) shows the result of optical reconstruction. It is clear that the holographic
image was successfully observed at the target observation point via the see-throughholographic screen of DDHOE.
5. Conclusion
An overview of wavefront printing technique and its some applications: 3D data visualizationand fabrication of digitally designed HOE to be used on the projection-type holographic 3D
display, were introduced. In the future work, the full-color wavefront printer and speed up ofrecording process will be handled.
6. Acknowledgement
This work was supported by JSPS KAKENHI grant number 26790064. This research anddevelopment work was supported by the MIC/SCOPE # 162103005.
6. References
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Y. Kim, et al. Optics Express, 23, 1, 172-182, (2015).
K. Wakunami, et al. Proc. SPIE 9867, 98670J, Baltimore, Maryland, USA (2016).
http://www.123dapp.com/
http://www.gsic.titech.ac.jp/en