Nanocomposite photonic crystal devices

Transcription

1 Nanocomposite photonic crystal devices Xiaoyong Hu, Cuicui Lu, Yulan Fu, Yu Zhu, Yingbo Zhang, Hong Yang, Qihuang Gong Department of Physics, Peking University, Beijing, P. R. China

2 Contents Motivation Photonic crystal all-optical switching Photonic crystal all-optical diode Conclusion

3 Motivation Information carriers: photon and electron Information processing rate: photon ~ Tbit/s Electron ~ Gbit/s Ultrahigh-speed light information processing need: All-optical switching, all-optical diode, Material is the basis of device: for electron: semiconductors (electron bandgap) for photon:? (photonic bandgap material)

4 photonic crystal Possess periodic dielectric distribution in space Have photonic bandgap and passband Physics idea of research Using third-order nonlinear optical material to form photonic crystal Third-order optical nonlinearity All-optical tuning dielectric distribution Refractive index n = n + 0 n2i All-optical tuning photonic band structure Realize photonic device

5 photonic crystal all-optical switching Propagation states of signal light controlled by a pump light Realization method:photonic bandgap shift or defect mode shift ON : Signal light Photonic crystal T Defect mode Signal light V OFF : Signal light Pump light Photonic crystal Third-order nonlinear Kerr effect: T Pump light V Signal light n Pump = n n I intensity Large n 2 Low I

6 Key characteristics of all-optical switching: Low operating pump power High switching efficiency Ultrafast switching time Requirement for nonlinear materials: Large nonlinear susceptibility Ultrafast response time

7 Optical nonlinearity of conventional materials: NLO materials n 2 (m 2 /W) t(s) Liquid crystal Semiconductor Organic polymers Large nonlinear susceptibility and ultrafast response are difficult to achieve simultaneously

8 Typical silicon photonic crystal optical switching Pump intensity: 10 GW/cm 2 Response time: 50 ps Switching efficiency: 90% Appl. Phys. Lett. 87, (2005) Typical Organic photonic crystal optical switching Pump intensity: 9 GW/cm 2 Response time: 120fs Switching efficiency: 70% Transmittance (%) Time Delay (fs) Appl. Phys. Lett. 87, (2005);

9 Questions exist for all-optical switching: High pump power ~ GW/cm 2 order; Ultrafast response and low-power is difficult to reach simultaneously; resolutions: Construct material with large and ultrafast nonlinearity

10 How about nanocomposite material? P3HT PCBM (1) Nano-Ag:MEH-PPV 800nm probe MEH-PPV Energy transfer ~35ps Ag nanopartical SPR resonant excitation (2) Nano-Ag:(PCBM:P3HT) SPR enhanced charge transfer and exciton-exciton annihilation ~ps Ag nanopartical SPR resonant excitation 800nm probe

11 2D nanocomposite photonic crystal sample Fabrication: spin coating + FIB etching Photonic crystal microcavity 2D photonic crystal Film thichness: 450nm Lattice constant: 320nm Air hole radius: 120nm Line defect width: 440nm Film thichness: 450nm Lattice constant: 260nm Air hole radius: 100nm

12 Experimental setup Ti:sapphire Laser Femtosecond pumpprobe method was used 400nm pump 800 nm probe BBO Crystal Filter Aperture Prism Lens Ti:sapphire laser Paluse width: 120fs Pulse repetition: 76MHz Tunable range: 700nm- 860nm Delay Line Fiber Spectrophotometer Micro Lens PMT Computer

13 Nanocomposite material Nano-Ag:MEH-PPV Physics idea: SPR enhancing nonlinearity + Energy transfer (3) The effective third-order nonlinear susceptibility χ : Metal contribution In the SPR peak ε + ε 0 m 2 h a very large nonlinear susceptibility

14 Absorption spectrum 400nm pump laser drop in the absorption band of MEH-PPV and near the SPR peak of Ag nanoparticles SPR resonant excitation Average diameter of Ag nanoparticles is 15nm Absorption (a.u.) 4 (MEH-PPV)+Ag film MEH-PPV film Ag colloid Doping concentration is 30% Wavelength (nm)

15 All-optical switch effect Pump power: 230 KW/cm 2 Response time: 35ps Switching efficiency: 65% Transmittance (%) Time Delay (ps) Appl. Phys. Lett. 94, (2009)

16 Multi-component nanocomposite Physics idea: nano-ag:(pcbm:p3ht) SPR enhancing nonlinearity + local-field enhancing nonlinearity Dielectric contribution Metal contribution Nonuniform field distribution of laser between different components local-field enhancing nonlinearity In the SPR peak ε + ε 0 m 2 h SPR enhancing nonlinearity

17 Absorption spectrum 400nm pump laser drop in the absorption band of P3HT, PCBM, and near the SPR peak of Ag nanoparticles SPR resonant excitation

18 All-optical switching effect Pump intensity: 70 kw/cm 2 (reduced by 5 order) Response time: 30 ps Switching efficiency: 60% Appl. Phys. Lett. 99, (2011)

19 Expand to optical communication range 1D metal-dielectric photonic crystal Physics idea: Bragg resonance enhancing nonlinearity quantum confinement enhancing nonlinearity effective third-order nonlinear susceptibility : Dielectric material contribution: Enhanced by quantum confinement effect metal contribution: Enhanced by Bragg resonance effect Very large

20 Gold/polycrystal lithium niobate photonic crystal: Fabrication: pulsed laser deposition(pld) Gold layer thickness: 10 nm LiNbO3 layer thickness: 150 nm Bragg resonance enhancing nonlinearity: LiNbO3 Au LiNbO3 Au Spatially periodic dielectric structure Strong Bragg resonance Strong field distribution in Au layer LiNbO3 Enhancing nonlinearity Au SiO2 AFM image of LiNbO3 layer surface roughness < 4.5 nm Formed by small crystal grains Quantum confinement enhancing nonlinearity AFM image for gold layer Surface roughness < 2 nm

21 Experimental setup Fs pump and probe method Pump beam: 1300nm Probe beam : 1300nm Pulse Duration Pulse Repetition 35fs 1kHz Ti:sapphire Laser 1300nm Aperture 1300nm Lens Delay Line Computer PMT Monochromator

22 Measured all-optical switching effect Operating wavelength: 1300nm Pump power: 9 MW/cm 2 (reduced by 3 order) Response time: 24 ps Switching efficiency: 80% Ultrafast relaxation of nonequilibrium electrons in gold ensure ultrafast response Adv. Mater. 23, 4295 (2011)

23 Reported by PhysOrg.com:

24 Nanomaterials world 5 (2009,Mar. 17) 5 Reported by Nanomaterials World:

25 Photonic crystal all-optical diodes nonreciprocal transmission properties: Transmitting light only in one direction signal light Photonic crystal Blocking light in the reverse direction Photonic crystal signal light

26 Realization method: Strong optical nonlinearity and asymmetric structure to break time-reversion symmetry Questions for all-optical diode: High operating power ~ GW/cm 2 order Low transmission contrast < 90 ( transmission contrast between two direction )

27 Asymmetric nanocomposite photonic crystal microcavity Physics idea: SPR enhancing nonlinearity + dynamic coupling of asymmetrical microcavity modes Thickness: 450 nm Nano-Au:MEH-PPV Lattice constant: 210 nm Air hole diameter: 138 nm Rightward Leftward A width: 312 nm B width: 485 nm A B

28 Measured transmission spectrum 0.5 nm wavelength detune of A and B mode Transmittance (%) Incident light B A Wavelength (nm) Rightward incidence case: Much incident light couple to mode A leftward incidence case: small incident light couple to mode A Rightward A B Leftward Origination of nonreciprocal transmission : Energy coupled to mode A is different Shift of mode A and coupling of modes A and B are different Transmission is different

29 All-optical diode effect Transmittance (%) Rightward Leftward 6.3 Photon Intensity (MW/cm 2 ) 8.4 Threshold operating intensity: 2.1 MW/cm 2 (reduced by 5 orders) Transmission contrast: (enlarged by 3 orders) Adv. Funct. Mater. 21, 1803 (2011)

30 Reported by Renewable Energy:

31 Conclusion Large nonlinear susceptibility and ultrafast response time of ps order were achieved An ultrafast low-power photonic crystal all-optical switch was realized by use of composite materials An low-power all-optical diode is realized

32 Thank you