1. 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: +86-10-62756567qhgong@pku.edu.cn

2. Contents  Motivation  Enhanced ultrafast 3rd nonlinearity using composite materials  Photonic crystal and PC optical switch  Conclusion

3. I.Motivation 1980- Third-order Optical Nonlinear Materials Photonics Applications Fast and large 3 rd NLO response fs NLO response large off-resonant  (3) All optical device Optical switching Optical computing  conjugated organic molecules and polymers Semiconductors } fs measur. Integrated photonic circuits

4. Femtosecond OKE System  : 760 - 850nm  : ～ 100fs I 1 :I 2 = 10:1 Measurement on ultrafast 3 rd nonlinearity

5. E1E1 E2E2 EsEs IsIs I1I1 I2I2  (3) E2E2 E1E1 EsEs 45 0 Is =Is = P Typical OKE signal of CS 2 OKE – four wave mixing process

6. 3 rd optical nonlinearity of routine materials ： NLO materials n 2 (m 2 /W) t(s) Organic polymers 10 -16 -10 -17 10 -15 Semiconductor 10 -17 10 -13 ☆ Large 3 rd nonlinear susceptibility and ultrafast response are difficult to achieve simultaneously Liquid crystal 10 -7 10 -6

7. Composite I: Coumarine 153 doped Polystyrene * Inter-molecular excited-state electron transfer II Enhanced ultrafast 3 rd nonlinearity using composite materials n 2 (  (3) ) ~ 1/(  0 –  – i  ) * Near resonant enhancement (enlarge the response time of excited state lifetime )

8. 800nm probe Inter molecular electron transfer C153 molecule ~ 1ps Coumarine 153 doped Polystyrene Polystyrene 400nm near-resonant excitation Polymer composite material: C153:Polystyrene

9. The effective third-order nonlinear optical susceptibility of the composite material can be written as and are permittivity for host material and metal nanoparticles and are third-order optical susceptibility of host material and metal nanoparticles In the SPR peak a very large nonlinear coefficient p is the volume fraction of Ag nanoparticles Composite Material II: Nano-Ag doped MEH-PPV surface plasmonics enhanced 3 rd optical nonlinearity

10. Nano-Ag doped MEH-PPV Ag nanoparticle Energy transfer ～ ps MEH-PPV SPR resonant excitation

11. ★ 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

12. Defect Radius Dielectric Defect Frequency 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

13. 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 State Photonic Bandgap Defect State Shift Pump Beam Intensity Light beam controlled Shift

14. Concept for All-Optical Switching effect Probe light Pump light Using Photonic bandgap shift or defect state shift by Pump Beam Photonic crystal optical switching Probe light

15. Schematic Structure of Polystyrene Molecule Organic polymer: Polystyrene n 2 = 1×10 -13 cm 2 /W 1) PC optical switch using pure polymer

16. 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 etching cylindrical air holes embodied in the polystyrene slab. The patterned area is about 4 μm×100 μm

17. Transmission spectra : (a) Measured result (b) Theoretical result of multiple scattering method Photonic Crystal Devices: Filter, Switch line defect transmission mode * Central Wavelength 791nm, Quality Factor 500, Line width 1.6nm

18. 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 StructureElectric-field Distribution W θpθp Waveguide Substrate Air Gap Substrate Waveguide Prism Mode Guided Mode Air Gap X Z probe beam

19. Experimental Setup Ti:sapphire laser: Pulse Duration 120fs Pulse Repetition 76MHz Wavelength 700nm － 860nm PMT Computer Monochromator Prism LensAperture Ti:sapphire Laser Diode Delay Line Micro Lens Waveguide 100 μm×2.5 mm The patterned area is about 4 μm×100 μm 800nm Pump beam 800nm

20. 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/cm 2 800nm Pump beam Switching Performance

21. 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

22. Electric field distribution of defect mode Electric field was mainly confined in the defect structure

23. 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

24. Experimental setup Ti:sapphire Laser PMT Computer Fiber Spectrophotometer Prism LensAperture Delay Line Micro Lens BBO Crystal Filter Near-resonant enhanced ----- 400nm Pump beam ☆ Near-resonant enhanced nonlinearity of polystyrene 400nm 800nm

25. Response time: 1.2ps All-optical switch effect Switching efficiency: 80% Pump power: 110 KW/cm 2 (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 ”

26. 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’

27. 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。

28. 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.

29. 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 ）。

30. Response time: 35ps Switching efficiency: 65% Pump power: 230 KW/cm 2 Appl. Phys. Lett. 94, 031103 (2009) SPP resonant-enhancement 3) Nano-Ag:MEH-PPV PC optical switch

31. 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

32. 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.

33. 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 3 rd nonlinear susceptibility (4-orders enhanced ) and ultrafast response time ( of ps order ) were achieved

34. Financial Supported by: NNSFC, China MOST, China MOE, China, Peking Uiversity V. Acknowledgement

35. THE END Thank You!