Supplementary Information
Chip-integrated all-optical diode based on nonlinear plasmonic
nanocavities covered with multicomponent nanocomposite
by Zhen Chai, Xiaoyong Hu,* Hong Yang, and Qihuang Gong*
Dr. Z. Chai, Prof. X. Y. Hu, Prof. H. Yang, Prof. Q. H. Gong
State Key Laboratory for Mesoscopic Physics & Department of Physics,
Collaborative Innovation Center of Quantum Matter,
Peking University, Beijing 100871 (PR China)
E-mail: [email protected], [email protected]
Prof. X. Y. Hu, Prof. H. Yang, Prof. Q. H. Gong
Collaborative Innovation Center of Extreme Optics,
Shanxi University, Taiyuan, 030006 (P. R. China)
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The Supplementary Information contains text and figures in support of the main body of the
manuscript. It discusses the following topics:
1. Fabrication of the multicomponent nanocomposite nano-Au:(IR140:MEH-PPV) layer
2. Fabrication of the plasmonic microstructure with nano-Au:(IR140:MEH-PPV) cover layer
3. Dispersion relations of the plasmonic waveguide having nano-Au:(IR140:MEH-PPV)
cover layer
4. The micro-spectroscopy measurement system
5. Calculated the excitation coupling efficiency of the plasmonic grating
6. The closed-aperture Z-scan measurement method
2
1. Fabrication of the multicomponent nanocomposite nano-Au:(IR140:MEH-PPV) layer
a) Fabrication of IR140:MEH-PPV composite solution
Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) powder with an
average molecular weight of 100,000 (Sigma Aldrich Company, USA) was dissolved in chloroform
with a weight of 1:180. Organic chromophore IR140 powder (Sigma Aldrich Company, USA) with
an average molecular weight of 779.19 was added in the MEH-PPV solution with a doping
concentration of 15%. The composite solution was vibrated by ultrasonic wave for four hours to
ensure that both solvents are solved completely.
b) Synthesis of gold nanoparticles
All chemicals were obtained from commercial sources (Sigma Aldrich Company, USA) and
were used without further purification. An aqueous solution of HAuCl4 (400 μL, 1% wt) was added
quickly to the ultrapure water (40 mL), which was magnetically stirred under the 40 ºC
water-bath heating. Trienthanolamine (TEA) (2.984 g) was dissolved in ultrapure water (20 mL).
Next, freshly prepared TEA aqueous solution (0.8 mL, 1 M) was injected quickly into the solution
under vigorous stirring. The growth reaction was performed at 40 ºC under gentle stirring for about
one hour. The synthesized gold nanoparticles were purified from the excess solution by
centrifugation (9500 rpm for 5 min) twice before further use.
c) Fabrication of nanocomposite nano-Au:(IR140:MEH-PPV) layer
The synthesized gold nanoparticles were added into the composite solution of IR140:MEH-PPV
with a doping concentration of 20 %, which was vibrated by ultrasonic wave for one hour to ensure
good
homogeneity
of
films.
Spin
coating
nano-Au:(IR140:MEH-PPV) nanocomposite layer.
3
was
used
to
fabricate
80-nm-thick
2. Fabrication of the plasmonic microstructure with nano-Au:(IR140:MEH-PPV) cover layer
The gold film was fabricated by using a laser molecular beam epitaxy (LMBE) growth system
(Model LMBE 450, SKY Company, China). The beam (with a wavelength of 248 nm and a pulse
repetition rate of 5 Hz) output from an excimer laser system (Model COMPexPro 205, Coherent
Company, USA) was used as the excitation light source. The beam was focused onto a gold target
mounted on a rotating holder, 10 mm away from the SiO2 substrate. The typical energy density of
the laser pulse was 400 mJ/cm2. The growth rate measured by a film thickness/rate monitor was
0.01 nm/pulse. The thickness of the gold films was 300 nm on the SiO2 substrate. A focused ion
beam etching system (Model Helios NanoLab 600, FEI Company, USA) was used to prepare the
patterns of the plasmonic microstructure sample. Spin coating was used to fabricate 150-nm-thick
nano-Au:(IR140:MEH-PPV) nanocomposite layer on the surface of the plasmonic microstructue
sample.
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3.
Dispersion relations of the plasmonic waveguide having nano-Au:(IR140:MEH-PPV) cover
layer
The calculated dispersion relations of the plasmonic waveguide with nanocomposite cover
layer by using the finite element method is shown in Fig. S1. According to the Maxwell Garnett
theory,
the
effective
dielectric
constant
 eff
of
the
nanocomposite
material
nano-Au:(IR140:MEH-PPV) can be calculated by the relation [1]
 e f f  h
 h
p m
 e f f 2 h
 m  2 h
where  m
and  h
(1)
are the dielectric constant of gold and the background medium
IR140:MEH-PPV, respectively. p is the volume fraction of gold nanoparticles. The dielectric
constant  h of the background medium IR140:MEH-PPV was set to be 1.6 in our calculation. The
frequency dependent complex dielectric function of gold was obtained from Ref. [2]. It is clear that
the plasmonic waveguide can provides wide band SPP modes. This is also confirmed by the
calculations of Li et al. [3].
Frequency (2c/d)
0.24
0.20
0.16
0.10
0.12
0.14
Propagation Constant (2d)
Figure S1. Calculated dispersion relations of the plasmonic waveguide with nanocomposite cover
layer.
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4. The micro-spectroscopy measurement system
A p-polarized CW Ti:sapphire laser system (Model Mira 900F, Coherent Company, USA) was
used as the light source. The line width of the laser spectrum curve was only 1.7 nm, which ensures
that only the needed quasi-monochromatic SPP mode can be excited in the plasmonic waveguide.
The coupling grating was normally illuminated from the back side. The optical-thick gold film can
prohibit the direct transmission of the incident laser beam. The SPP mode propagating through the
plasmonic waveguide was scattered using decoupling grating in the output port. The scattered light
was collected by a long working distance objective (Mitutoyo 20, NA=0.58) and then imaged onto a
charge coupled device (CCD). To study the all-optical tunability of the plasmon-induced
transparency and the all-optical diode performance, we used the 120-fs laser beam (with a pulse
repetation rate of 76 MHz) from a Ti:sapphire laser system (Model Mira 900F, Coherent Company,
USA) as the light source.
CCD
Lens
Microscope objective
Sample
Ti:sapphire laser
Microscope objective
Mirror
Figure S2. Experimental setup of micro-spectroscopy measurement system.
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5. Calculated the excitation coupling efficiency of the plasmonic grating
To evaluate the SPP excitation coupling efficiency, we calculated the magnetic-field
distribution of the plasmonic waveguide, having the coupling grating connecting with a triangular
air groove in the input port, covered with the nanocomposite layer under excitation with different
incident light by using the finite element method, and the calculated results are shown in Fig. S3.
The coupling losses were caused by inefficient photon-to-SPP conversion and subsequent
inefficient coupling into the 100-nm-wide plasmonic waveguide.
The calculated magnetic-field distribution of the plasmonic waveguide, having the coupling
grating connecting with a triangular air groove in the input port, under excitation with a 740 nm
incident light is shown in Fig. S3(a). The incident magnetic-field intensity was 1.45937 a.u. in the
back side of the coupling grating. Small magnetic-field intensity of 0.11651a.u. was obtained in the
input port of the plasmonic waveguide due to the coupling losses and triangular air groove
collecting losses. Therefore, if the incident power was P0, the power reaching the plasmonic
nanocavities was P0×(0.11651/1.45937), i.e., P0×7.983%. So, the coupling efficiency of the
plasmonic grating was 7.983% at the wavelength of 740 nm.
The calculated magnetic-field distribution of the plasmonic waveguide, having the coupling
grating connecting with a triangular air groove in the input port, under excitation with a 775 nm
incident light is shown in Fig. S3(b). The incident magnetic-field intensity was 1.32617 a.u. in the
back side of the coupling grating. Small magnetic-field intensity of 0.10243 a.u. was obtained in the
input port of the plasmonic waveguide due to the coupling losses and triangular air groove
collecting losses. Therefore, if the incident power was P0, the power reaching the plasmonic
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nanocavities was P0×(0.10243/1.32617), i.e., P0×7.723%. So, the coupling efficiency of the
plasmonic grating was 7.723% at the wavelength of 775 nm.
The calculated magnetic-field distribution of the plasmonic waveguide, having the coupling
grating connecting with a triangular air groove in the input port, under excitation with an 820 nm
incident light is shown in Fig. S7(c). The incident magnetic-field intensity was 1.17857 a.u. in the
back side of the coupling grating. Small magnetic-field intensity of 0.07466 a.u. was obtained in the
input port of the plasmonic waveguide due to the coupling losses and triangular air groove
collecting losses. Therefore, if the incident power was P0, the power reaching the plasmonic
nanocavities was P0×(0.07466/1.17857), i.e., P0×7.183%. So, the coupling efficiency of the
plasmonic grating was 7.183% at the wavelength of 820 nm.
The calculated magnetic-field distribution of the plasmonic waveguide, having the coupling
grating connecting with a triangular air groove in the input port, under excitation with an 860 nm
incident light is shown in Fig. S7(d). The incident magnetic-field intensity was 1.32775 a.u. in the
back side of the coupling grating. Small magnetic-field intensity of 0.093316 a.u. was obtained in
the input port of the plasmonic waveguide due to the coupling losses and triangular air groove
collecting losses. Therefore, if the incident power was P0, the power reaching the plasmonic
nanocavities was P0×(0.093316/1.32775), i.e., P0×7.016%. So, the coupling efficiency of the
plasmonic grating was 7.016% at the wavelength of 860 nm.
As, a result, the photon-to-SPP coupling efficiency of the input-coupling grating was more
than 7% in a wideband wavelength range from 740 to 860 nm.
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a
b
d
c
Figure S3. Calculated magnetic-field distribution of a plasmonic waveguide, having the coupling
grating connecting with a triangular air groove in the input port, covered with the nanocomposite
layer under excitation with an incident light at wavelengths of 740 nm (a), 775 nm (b), 820 nm (c),
and 860 nm (d).
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6. The closed-aperture Z-scan measurement method
An 800-nm, 120-fs laser beam (with a repetition rate of 76 MHz) output from a Ti: Sapphire
laser (Mira 900F, Coherent, USA) was used as the light source. The profile of the normalized
transmission curve indicates whether a positive or negative value of a nonlinear refractive index can
be obtained. The peak-valley profile of the curve indicates that the sample possesses a negative
nonlinear refractive index. While a valley-peak profile of the curve indicates that the sample
possesses a positive nonlinear refractive index. The normalized transmission can be fitted to[4]
T ( z)  1 
4x
( x  9)( x 2  1)
(2)
2
where T is the normalized transmittance, x=z/z0, z is the longitudinal distance from the focal point,
z0 is the Rayleigh range of the laser beam,  is the phase change, which is related to the
nonlinear refractive index n2 via[4]
n2 

2I 0 (1  e L )
(3)
where  is the laser wavelength,  is the linear absorption, I0 is the peak intensity of the laser
beam, L is the sample thickness. Quarterman et al. have pointed out that as an intrinsic material
parameter the value of the nonlinear refractive index was independent of the incident light power.[5]
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References
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crystals. Phys. Rev. B 1999, 60, 5359–5365.
[2] Johnson, P. B.; Christy, R. W. Optical constants of the noble metals. Phys. Rev. B 1972, 6,
4370–4379.
[3] Li, X. E., Jiang, T., Shen, L. F. & Deng, X. H. Subwavelength guiding of channel plasmon
polaritons by textured metallic grooves at telecom wavelengths. Appl. Phys. Lett. 2013, 102,
031606.
[4] Henari, F. Z.; Cazzini, K.; Akkari, F. E.; Blau, W. J. Beam waist changes in lithium niobate
during Z-scan measurement. J. Appl. Phys. 1995, 78, 1373-1375.
[5] Quarterman, A. H.; Tyrk, M. A.; Wilcox, K. G. Z-scan measurements of the nolinear refractive
index of a pumped semiconductor disk laser gain medium, Appl. Phys. Lett. 2015, 106, 011105.
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