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Plasmonic Hologram Based on Bilayer Metallic Nanowire Gratings
Xin Sheng1, Jie Cui1, Jun Zheng2, Zhi-cheng Ye*1 and Han-ping D. Shieh1, 3
1National Engineering Laboratory for TFT-LCD Materials and Technology, Department of Electronic
Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China 2Key Laboratory for Laser Plasmas (Ministry of Education), Department of Physics, Shanghai Jiao Tong
University, Shanghai, 200240, China 3Department of Photonics and the Display Institute, National Chiao Tung University,
Hsinchu 300, Taiwan
Abstract Holographic images were created with high contrast and low
noise by the enhancement of surface plasmon waveguiding effect.
The holograms are sensitive to polarization for compatibility with
further liquid crystal displays and can be reconstructed by white
light.
Author Keywords plasmonic hologram; 3D display; Surface Plasmon Resonance
(SPR); waveguide.
1. Introduction Holography technology has the ability to record the whole
information, which has been applied to many fields such as
holographic interferometry, three-dimensional holographic CAT
scans, credit cards and debit cards. Particularly, 3D holographic
display enjoys great popularity due to the advantage of true 3D
image without glasses. As one of the most successful examples,
3D holographic print from Zebra Imaging can be displayed with a
simple light source without the need of special equipment. 3D
hologram pictures, another example, have been used to present the
artwork for decoration and archival recordings. Unfortunately,
low diffraction efficiency and poor image contrast are still
troubling the holograms especially for the relief ones.
The combination of holography and SPR has been reported to
improve diffraction efficiency of hologram and based on it color
hologram was also demonstrated [1]. Surface Plasmon Resonance
(SPR) is the collective oscillation of electrons on a metal surface.
A light beam incident on the SPR hologram will couple with the
surface plasmon polaritons if they match the light momentum,
thus the diffraction efficiency is increased by the strong resonance
[2]. Normally, a prism or a grating is needed to excite SPR.
However, the prism type is bulky for hologram, and in the grating
coupling, it is difficult for light beam to satisfy the incident angle
precisely.
In fact, for a hologram with metal there are two kinds of surface
plasmon modes: lateral one along the hologram surface and
longitudinal one in the slits of the hologram reliefs. The previous
studies referred to the former, while the latter was neglected. In
our work, a major goal is to take full advantage of longitudinal
surface plasmon mode and to extend the utilization of SPR
holography. In our experiment, we coated the hologram with
aluminum to form a billayer metal film, and this new metal
hologram (Plasmonic Hologram) has a preference for TM
diffraction which shows enhanced efficiency and reduced noise
by improving image contrast. Meanwhile, monochromatic
holographic images were obtained by white light illumination,
which will be discussed in later section.
2. Theoretical and Experimental 2.1 Model of Plasmonic Hologram
As is known to all, the profile of the hologram is random fringe
pattern [3], in other word, an assembly of complex gratings with
line direction mainly perpendicular to the incident plane of the
object and reference beams. Therefore, we can simplify the metal
holographic pattern as metal gratings as shown in figure 1.
To show the waveguide modes in the metal-insulator-metal slits
of metal hologram clearly, equation (1) represents the dispersion
relationship deduced from Bloch theory.
)sin()sin()1
(2
1)cos()cos()cos( 22112211 tktk
ggtktkKT
(1)
Where, K is the Bloch wave number,T is pitch of the grating,
1t and 2t are the width of the dielectric and aluminum in one
period, respectively, 2
0
2
01 zkkk and 22
02 zm kkk are
the wave numbers of the input light in the air and aluminum along
the X-axis, respectively. zk is the wave number of the waveguide
mode along the Z-axis. 021 / kkg m for TM light and
21 / kkg for TE light [4].
Figure 1. Cross-section of metal grating: t1, t2 are the width of
air slit and metal slit, respectively. T denotes the period of
metal grating. For TE light, electric field is perpendicular to
plane of incidence; for TM light, electric field is parallel to
plane of incidence.
46.2 / X. Sheng
656 • SID 2014 DIGEST ISSN 0097-966X/14/4502-0656-$1.00 © 2014 SID
(a)
(b)
Figure 2. Dispersion of the Al-air-Al slits waveguide modes of
the Grating: (a) for TE light; (b) for TM light. The grey zone
is for visible light. The black line is the dielectric line of the
slit. The blue and red dots are the real and imaginary parts of
the wave number kz, respectively.
Figure 1 shows the metal grating, a schematic diagram of
plasmonic hologram model, where T is 320nm, both t1 and t2 are
160nm, the metal and insulator are specified to be aluminum and
air, respectively. According to this model, we can obtain the
solutions of equation (1) shown in figure 2. The intersection point
of kz-r1 and kz-i1 is called first-order cut-off frequency, which
means that only the frequencies above it, the first-order
waveguide modes can pass through the air slit. For TE light in
figure 2(a) the cut-off frequency is ~5×1015 Hz (~378nm) and
there is no real solution below it. For TM light in figure 2(b), a
line marked by kz-r0 is beneath the black dielectric line, which
means that TM zero-order waveguide mode is not cut off.
Accordingly, it is clear that TM is always supported to propagate
in the air slits via surface plasmon waveguide modes; nevertheless
TE is forbidden for its cut-off frequency is larger than the visible
light. In other word, TM light will be diffracted to reconstruct the
object while TE will not. Thus the polarized response of
plasmonic hologram is achieved.
2.2 Experimental
The figure 3 illustrates the experimental setup of hologram
recording. The beam is split into two parts after expansion; one
(the reference beam) is directly illuminating the recording plate
and the other is reflected from the object and then recorded. The
laser we used is a He-Cd gas laser with wavelength of 457.8nm.
The incident angle to the plate is 45° . The intensity after
expansion and the exposure time are 4mW/cm2 and 3minutes,
respectively. The exposed photoresist is developed with NaOH
(0.7%) for 10 seconds. Then, the hologram is rinsed with deioned
water and heated by hot wind for 20s and 30s, respectively.
Subsequently, a 40nm aluminum film is deposited onto the
hologram using e-beam coater (ZSX-500D). Figure 4 shows the
pattern coated with aluminum film. The thickness of aluminum
film is optimized according to that of photoresist. Please note that
the hologram not deposited with aluminum film is called
„ordinary hologram‟ in this paper.
Figure 3. Optical system for recording a transmission
hologram: A plane wave is incident at angle of 45°. The
object to be recorded is close to the recording plate to alleviate
phase difference blur.
Figure 4. The process of the ordinary hologram turning into
plasmonic hologram.
For reconstruction, one can use both the original reference laser
beam and white beam to obtain the image. Figure 5 shows the real
image reconstructed by original reference beam. We can see that
the details on the object (mirror image of the word “CHINA” on a
vertical key) could be represented clearly. As is known to all,
holograms do not reproduce the true colors of the original object.
The image‟s color depends on the color of the laser used to make
the hologram, so the reconstruction image is blue due to 457.8nm
laser beam. In our experiment, white light is also used to
illuminate the plasmonic hologram to achieve the monochromatic
holographic images.
Figure 6 are red/green/blue (R/G/B) real images reconstructed by
parallel white light (unpolarized). The angle of incidence is 75°.
The angles between R/G, G/B are 20°and 21°, respectively.
The viewing distance is 15cm, so that the R/G/B real images can
separate from each other and become more attractive than
traditional rainbow hologram. Because our plasmonic holograms
are image plane hologram, it is easy to obtain the monochromatic
holograms without any slits used in traditional fabrication.
46.2 / X. Sheng
SID 2014 DIGEST • 657
Figure 5. Reconstructed real image of plasmonic hologram: The incident angle is 80°, and the viewing angle is ~45°.
(a) (b) (c)
Figure 6. Red/green/blue real images observed in different viewing angle: (a) red: 43°; (b) green: 23°; (c) blue: 2°. The
wavelengths of R/G/B are 670, 550, 450nm, respectively.
3. Results and Discussion In the measurement, we compare the plasmonic hologram with
ordinary one. Meanwhile, as reconstruction beam, TM and TE
white light illuminate the hologram above separately [5]. The
results are shown as follows.
Figure 7. TE/TM parallel white light illuminates the
plasmonic hologram and ordinary hologram: (a) Reflection,
(b) Transmission, (c) Sum of transmission and Reflection, (d)
Diffraction efficiency as a function of wavelength.
Figure 7(a)-4(c) are reflection, transmission, the sum of
transmission and reflection as a function of wavelength,
respectively. From figure 7(a), it can be seen that the majority of
TE light is reflected by plasmonic hologram, up to 80%, but the
TM reflection is under 35%. In figure 7(c), compared with
ordinary hologram, there is a great disparity (30%~50%) between
TM and TE light in the sum of transmission and reflection for
plasmonic hologram. Obviously, the plasmonic hologram is
polarization-sensitive.
Figure 7(d) is first-order diffraction efficiency as a function of
wavelength. It is clear in figure 7(d) that the diffraction efficiency
was increased significantly, especially for TM light. At 457.8nm,
for example, diffraction efficiency for TM light jumps from 0.3%
to 4.2%. Moreover, with the increase in wavelength, plasmonic
hologram diffraction efficiency for TM light grows more sharply.
On the contrary, though showing the enhancement, diffraction
efficiency of TE light declines with the growth of wavelength,
which is matching with the cut-off effect of metal-insulator-metal
waveguides in plasmonic hologram. On the whole, for diffraction
efficiency of plasmonic hologram, the ratio of TM to TE light is
ranging from 1.7 to 6.5. These results are in agreement with the
theoretical analysis.
Image contrast is considered to evaluate the image quality. The
image contrast is defined as
minmax
minmax
II
IIV
(2)
In order to measure the image contrast of different wavelength,
we fixed the white light source position and its incident angle at
75 ° . For individual wavelength, the maximum/minimum
intensity was obtained by fine-tuning the height of spectrometer.
It is good that the minimum intensity was localized at the “dark
hole” shown in figure 5(a), because other bark area may be not
within the diffraction zone.
46.2 / X. Sheng
658 • SID 2014 DIGEST
Table 1. Image contrast of plasmonic hologram
Wavelength (nm)
contrast (TM) contrast (TE)
446.87 61.80% 56.90%
521.73 52.90% 39.90%
551.95 74.50% 48.50%
609.77 58.60% 30.90%
646.56 73.10% 36.20%
From table 1, we can see that the image contrast for TM light is
higher than TE. At 646.56nm, for example, contrast of TM is two
times as much as that of TE. What‟s more, difference between
TM and TE becomes larger with the growth of wavelength.
From what has discussed above, we can see that plasmonic
hologram greatly enhance diffraction efficiency. In addition, TM
light performs better than TE in the improvement of diffraction
efficiency and image contrast. Therefore, ambient light, most of
which is TE mode after being reflected by other objects, will be
restrained to diffract by plasmonic hologram, thus decreasing the
noise and improving the image quality.
4. Conclusions In summary, the plasmonic hologram was fabricated and images
with individual color (R/G/B) were observed. It was demonstrated
that plasmonic hologram significantly enhanced the TM polarized
diffraction efficiency, which shows good agreement with the
results from our model. TM light performed better than TE in
image contrast due to the fact that TM light functions as
reconstruction beam, while TE light is restrained by cut-off
frequency. Meanwhile, our plasmonic hologram can be
compatible with liquid crystals (LC) due to its polarization
character. We believe that this manuscript opens a new door for
high-efficiency and high-contrast holograms by the plasmonic
enhancement. The future work to fabricate reflective full color
plasmonic hologram will be shown in the very near future.
5. Acknowledgments This work was sponsored by 973 Program (2013CB328804) and
supported by National Natural Science Foundation of China
(Grant No. 61007025, 61370047, and 10905039) and Ministry of
Education (Grant No. 20100073120034 and 20090073120076).
6. References [1] Miyu Ozaki, Jun-ichi Kato, Satoshi Kawata, “Surface-
Plasmon Holography with White-Light Illumination,”
Science 332, 218-220 (2011).
[2] Shoji Maruo, Osamu Nakamura, and Satoshi Kawata,
“Evanescent-wave holography by use of surface-plasmon
resonance,” App. Opt. 36, 2343-2346 (1997).
[3] Lee Hyuk, Jin Sang Kyu, “Experimental study of volume
holographic interconnects using random patterns,” Appl.
Phys. Lett. 62, 2191-2193 (1993)
[4] Zhi-Cheng Ye, Jun Zheng, Shu Sun, Lin-Dong Guo, Shieh,
H.-P.D., “Compact Transreflective Color Filters and
Polarizers by Bilayer Metallic Nanowire Gratings on
Flexible Substrates,” Quantum Electronics, 19, 4800205
(2013)
[5] D. E. Smalley, Q. Y. J. Smithwick, V. M. Bover Jr, J.
Barabas and S. Jolly, “Anistropic leaky-mode modulator for
holographic video displays,” Nature 498, 313-317 (2013).
46.2 / X. Sheng
SID 2014 DIGEST • 659
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