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
Contents Motivation Photonic crystal all-optical switching Photonic crystal all-optical diode Conclusion
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)
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
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 0 + 2 Pump = n n I intensity Large n 2 Low I
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
Optical nonlinearity of conventional materials: NLO materials n 2 (m 2 /W) t(s) Liquid crystal 10-7 10-6 Semiconductor 10-17 10-15 Organic polymers 10-16 10-15 Large nonlinear susceptibility and ultrafast response are difficult to achieve simultaneously
Typical silicon photonic crystal optical switching Pump intensity: 10 GW/cm 2 Response time: 50 ps Switching efficiency: 90% Appl. Phys. Lett. 87, 151112 (2005) Typical Organic photonic crystal optical switching Pump intensity: 9 GW/cm 2 Response time: 120fs Switching efficiency: 70% Transmittance (%) 100 90 80 70 60 50 40 30-2000 -1000 0 1000 2000 Time Delay (fs) Appl. Phys. Lett. 87, 231111 (2005);
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
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
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
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
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
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 3 2 1 Doping concentration is 30% 0 200 400 600 800 1000 1200 Wavelength (nm)
All-optical switch effect Pump power: 230 KW/cm 2 Response time: 35ps Switching efficiency: 65% Transmittance (%) 100 80 60 40 20-40 -20 0 20 40 60 Time Delay (ps) Appl. Phys. Lett. 94, 031103 (2009)
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
Absorption spectrum 400nm pump laser drop in the absorption band of P3HT, PCBM, and near the SPR peak of Ag nanoparticles SPR resonant excitation
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, 141113 (2011)
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
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
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
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)
Reported by PhysOrg.com:
Nanomaterials world 5 (2009,Mar. 17) 5 Reported by Nanomaterials World:
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
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 )
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
Measured transmission spectrum 0.5 nm wavelength detune of A and B mode Transmittance (%) 100 80 60 40 20 Incident light B 0 635 640 645 650 655 660 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
All-optical diode effect Transmittance (%) 100 80 60 40 20 0 0 2.1 4.2 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: 11875 (enlarged by 3 orders) Adv. Funct. Mater. 21, 1803 (2011)
Reported by Renewable Energy:
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
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