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
Contents
Motivation
Enhanced ultrafast 3rd nonlinearity
using composite materials
Photonic crystal and PC optical switch
Conclusion
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
Femtosecond OKE System
: 760 - 850nm: ~ 100fs I1:I2 = 10:1
Measurement on ultrafast 3rd nonlinearity
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
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
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 )
800nm probe
Inter molecular electron transfer
C153 molecule
~ 1ps
Coumarine 153 doped Polystyrene
Polystyrene
400nm near-resonant excitation
Polymer composite material: C153:Polystyrene
)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
Nano-Ag doped MEH-PPV
Ag nanoparticle
Energy transfer ~ ps
MEH-PPV
SPR resonant excitation
★ 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
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
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
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
Schematic Structure of Polystyrene Molecule
Organic polymer: Polystyrene
n2= 1×10-13cm2/W
1) PC optical switch using pure polymer
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
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
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
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
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
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
Electric field distribution of defect mode
Electric field was mainly confined in the defect structure
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
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
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”
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’
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。
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.
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 ) 。
-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
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
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.
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
Financial Supported by:
NNSFC, China
MOST, China
MOE, China,
Peking Uiversity
V. Acknowledgement
THE END
Thank You!
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