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: qhgong@pku.edu.cn; 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!