Qihuang Gong, Xiaoyong Hu, Jiaxiang Zhang, Hong Yang
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Transcript of Qihuang Gong, Xiaoyong Hu, Jiaxiang Zhang, Hong Yang
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Qihuang Gong, Xiaoyong Hu, Jiaxiang Zhang, Hong Yang
Department of Physics, Peking University, Beijing, P. R. China
Composite Materials for Ultrafast and Large Third-order Optical Nonlinearity
and Photonic Applications
Email: [email protected]; Fax: +86-10-62756567
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Contents
Motivation
Enhanced ultrafast 3rd nonlinearity
using composite materials
Photonic crystal and PC optical switch
Conclusion
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I. Motivation
1980- Third-order Optical Nonlinear Materials
Photonics Applications
Fast and large 3rd NLO response
fs NLO responselarge off-resonant (3)
All optical deviceOptical switching Optical computing
conjugated organic molecules and polymersSemiconductors
} fs measur.
Integrated photonic circuits
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Femtosecond OKE System
: 760 - 850nm: ~ 100fs I1:I2 = 10:1
Measurement on ultrafast 3rd nonlinearity
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E1
E2
Es
Is
I1I2
(3)
E2
E1Es
450
I
s = 211αd
αd2(3)44
020
22
s IIIeαd
e1χ
cnε
dωI
P
Typical OKE signal of CS2
OKE – four wave mixing process
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3rd optical nonlinearity of routine materials :
NLO materials n2(m2/W) t(s)
Organic polymers 10-16 -10-17 10-15
Semiconductor 10-17 10-13
☆ Large 3rd nonlinear susceptibility and ultrafast response
are difficult to achieve simultaneously
Liquid crystal 10-7 10-6
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Composite I: Coumarine 153 doped Polystyrene
* Inter-molecular excited-state electron transfer
II Enhanced ultrafast 3rd nonlinearity using composite materials
n2 ((3)) ~ 1/(0 – – i)
* Near resonant enhancement (enlarge the response time of excited state lifetime )
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800nm probe
Inter molecular electron transfer
C153 molecule
~ 1ps
Coumarine 153 doped Polystyrene
Polystyrene
400nm near-resonant excitation
Polymer composite material: C153:Polystyrene
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)3(m
2
hm
h
2
hm
h)3(h
)3(
2
3
2
331
pp
The effective third-order nonlinear optical susceptibility of the composite material can be written as
)3(
and are permittivity for host material and metal nanoparticlesh m
and are third-order optical susceptibility of host material and metal nanoparticles)3(
h )3(m
In the SPR peak 02 hm a very large nonlinear coefficient
p is the volume fraction of Ag nanoparticles
Composite Material II: Nano-Ag doped MEH-PPV
surface plasmonics enhanced 3rd optical nonlinearity
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Nano-Ag doped MEH-PPV
Ag nanoparticle
Energy transfer ~ ps
MEH-PPV
SPR resonant excitation
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★ Photonic crystal is a novel photonic material with a
One-dimensional Photonic crystal
Two-dimensional photonic crystal
Three-dimensional photonic crystal
★ Photonic crystal possesses photonic bandgap and
periodic dielectric distribution
can control the propagation states of photons
III. Photonic crystal and PC optical switch
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Defect Radius
Dielectric DefectFrequency
Air Defect
Air Band
Dielectric Band
Defect states
When a structure defect is introduced in the photonic crystal, the defect states will appear in the photonic bandgap
Photonic
Bnadgap
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Photonic Bandgap Shift
☆ Third-order optical nonlinear photonic crystal
Bandgap or Defect state shift ---------- change the refractive index
Probe LightPump Light
Wavelength
Transmittance Photonic Bandgap
Pump LightProbe Light
Transmittance
Wavelength
Defect StatePhotonicBandgap
Defect State Shift
Innn 20 Pump Beam Intensity
Light beam controlled Shift
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Concept for All-Optical Switching effect
Probe lightPump light
Using Photonic bandgap shift or defect state shift by Pump Beam
Photonic crystal optical switching
Probe light
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Schematic Structure of Polystyrene Molecule
Organic polymer: Polystyrene
n2= 1×10-13cm2/W
1) PC optical switch using pure polymer
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Film Thickness 300nm
Lattice Constant 320nm
Radius of Air Hole 130nm
Width of Line Defect 450nm
Two-dimensional Polystyrene Photonic Crystal Fabrication Process
A line defect in the center of a two-dimensional photonic crystal to form photonic crystal filter
Spin Coating + FIB etchingcylindrical air holes embodied in the polystyrene slab.
The patterned area is about 4 μm×100 μm
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Transmission spectra :
(a) Measured result
(b) Theoretical result of multiple scattering method
Photonic Crystal Devices:
Filter, Switch
760 780 800 8200
20
40
60
80
100
600 700 800 900 10000
20
40
60
80
100
(a)Tra
nsm
itta
nce (
%)
Wavelength (nm)
(b)
Tra
nsm
itta
nce (
%)
Wavelength (nm)
line defect
transmission mode
* Central Wavelength 791nm, Quality Factor 500, Line width 1.6nm
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Evanescent Field Coupling System
2) Coupling efficiency ~ 20%
1) Energy of the incident light is coupled into optical waveguide with the help of evanescent field
Cross Section Structure Electric-field Distribution
W
θp
Waveguide
Substrate
Air Gap
Substrate
Waveguide
Prism Mode
Guided Mode
Air Gap
X
Z
probe beam
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Experimental Setup
Ti:sapphire laser:
Pulse Duration 120fs
Pulse Repetition 76MHz
Wavelength 700nm -860nm
PMTComputer
Monochromator
Prism
LensAperture
Ti:sapphire Laser
Diode
Delay LineMicro Lens
Waveguide
100 μm×2.5 mm
The patterned area is about 4 μm×100 μm
800nm Pump beam
800nm
800nm
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Time Response ( as fast as the time-resolution of measurement system )
Conclusion:
An all-polymer tunable photonic
crystal filter, switch with
ultrafast time response is
realized.
* Transmittance Contrast 60%
* Time Response ~ 120fs
Pump Intensity as high as GW/cm2
800nm Pump beamSwitching Performance
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2) C153:Polystyrene PC optical switch
Lattice constant: 320nm
Air hole radius: 120nm
Film thichness: 300nm
Line defect width: 440nm
Polystyrene doped with 15% Coumarin 153
Absorption peak of Coumarin 153 is around 400nm
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Electric field distribution of defect mode
Electric field was mainly confined in the defect structure
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Measured result Simulated result
Transmittance spectra of the microcavity resonant mode as functions of the energy of the pump light
Tunability of the photonic bandgap microcavity
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Experimental setup
Ti:sapphire Laser
PMTComputer
Fiber Spectrophotometer
Prism
LensAperture
Delay LineMicro Lens
BBO Crystal
Filter
Near-resonant enhanced ----- 400nm Pump beam
☆ Near-resonant
enhanced nonlinearity
of polystyrene
400nm
800nm
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Response time: 1.2ps
All-optical switch effect
Switching efficiency: 80%
Pump power: 110 KW/cm2
(reduced by 4 orders)
Nature Photonics 2 (2008) 185-189
Chinese patent: 发明专利( ZL200710099383.2)“降低全光开关泵浦功率的方法、全光开关及其制备方法”
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Nature Photonics
A strongly nonlinear photonic crystal with a wavelength-tunable bandgap could provide the solution to realizing all-optical switches for signal processing‘
‘Controlling photons with light’
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IOP optics.org:
‘ Photonic crystals speed up all-optical switching’
A polystyrene photonic crystal that acts as an all-optical switch boasts picosecond response time and low power requirements. The picosecond switching time is impressive. 一种光子晶体开关以具备皮秒时间响应和低泵浦功率而值得自豪,皮秒的超快开关时间令人印象深刻。
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Nature Asia Materials:
Ultrafast Optical Switches: Now you see it, now you don’t
Researchers from Peking University, China, now demonstrate fast all-optical switching in a photonic crystal made from a composite material.
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Nature China: “Optical Switches: A New Low”
Qihuang Gong and co-workers at the Peking University in Beijing have devised a strategy for making ultrafast photonic-crystal-based optical switches that can operate under low-power pump light ) 。
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-40 -20 0 20 40 6020
40
60
80
100
Tra
nsm
itta
nce
(%
)Time Delay (ps)
Response time: 35ps
Switching efficiency: 65%
Pump power: 230 KW/cm2
Appl. Phys. Lett. 94, 031103 (2009)
SPP resonant-enhancement
3) Nano-Ag:MEH-PPV PC optical switch
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PhysOrg.com:
‘ Nanocomposite material provides photonic switching’ The development of
integrated photonic devices in
tomorrow’s technology is taking place today at Peking University in Beijing, China, where a group
of scientists has manufactured and
tested nanocomposite
material that could be used in integrated photonic devices
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Nanomaterials World :
“Seeing the light”Nanomaterials world 5 (2009,Mar. 17) 5
Photonic devices could aid developments in computing, following research in China.The team from Peking University is working on a nanocomposite that could be integrated into photonic devices.
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IV. Conclusion
☆ An ultrafast low-power photonic crystal all-optical
switch was realized by using the composite materials
☆ New composite materials are demonstrated to
develop the 3rd optical nonlinearity
☆ Large 3rd nonlinear susceptibility (4-orders enhanced )
and ultrafast response time ( of ps order ) were achieved
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Financial Supported by:
NNSFC, China
MOST, China
MOE, China,
Peking Uiversity
V. Acknowledgement
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THE END
Thank You!