Nanophotonic Devices for Classical and Quantum Information Processing

Transcription

1 Nanophotonic Devices for Classical and Quantum Information Processing Yiyang Gong, Dirk Englund, Bryan Ellis, Andrei Faraon, Jesse Lu Maria Makarova, Arka Majumdar, Kelley Rivoire, Gary Shambat, and Jelena Vučković Stanford University Nano-tech/Bio workshop, Stanford, CA, Feb. 2010

2 Nanoscale and quantum photonics group Quantum dots (QDs), Nanophotonic structures: research Q-wells,nanocrystals: Nanoscale localization and manipulation of light Light emitters + 4xMQW InGaAsP 200nm quantum photonics Optical communications and interconnects classical info. processing 0.2nm (devices for quantum info. processing, single QD modulators & switches) (High speed, low threshold lasers, optical switches, modulators - Silicon CMOS compatible) High-density nanophotonic and quantum circuits

3 Photonic crystals/plasmonic gratings Photonic crystal cavity Plasmonic structure Confinement by: distributed Bragg reflection (in plane) Total internal reflection (out of plane) localize light into extremely small volumes V< (λ/n)3 high quality factors Q (long photon storage times) Confinement by Collective charge oscillation at metaldielectric interface Confinement into V<<(λ/n)3, breaks diffraction limit moderate quality factors Q (ohmic losses) 3

4 Outline Er-doped silicon nitride photonic crystal and plasmonic light sources at telecom wavelengths (~1550nm) Germanium-Silicon electrically injected LED at 1550nm Photonic crystal lasers and electro-optic modulators Photonic crystal cavities at visible wavelengths 4

5 Enhancement of Er-doped amorphous Silicon nitride by photonic crystal and plasmonic structures Stanford University

6 Er-doped silicon photonic crystal cavities a = 410nm Theory: Q=32,000, V=0.85(λ/n) 3 Experiment: Q>15,000 Hybrid membrane: 110 nm Er:SiN x 250nm Si L. Dal Negro et al, IJSTQE 12, 6, 1628 (2006) Er doped Silicon rich nitride PL@10K PL@300K M. Makarova*, Y. Gong*, et. al. IEEE J. Sel. Top. Quant. Electronics Vol 16, pp (2010)

7 Linewidth narrowing in Er-doped silicon photonic crystal cavities Cavity Q increases with pump power at low temperature (from to 9,000 to 13,300)! Estimate: ~30% of Er atoms inverted Note: effect not visible in larger microring cavities Saturation of cavity emission observed for high pump powers Can reduce material losses by removing Si from cavity design Y. Gong, M. Makarova et al, Optics Express 18, 2601 (2010)

8 Purcell effect in Er-doped silicon photonic crystal cavities Purcell factor at room T: 2.4 Purcell factor at low T: Y. Gong, M. Makarova et al, Optics Express 18, 2601 (2010)

9 Plasmonic Er-Si light sources Co-sputterting Er:SiN x B Material easily incorporated in metal-insulator-metal (MIM) structure Growing nitride or oxide layer on metal is much easier than liftoff needed to make III-V structures based MIM Our case: 52nm thickness of Erdoped amorphous silicon rich nitride in MIM E 2 2 µm Y. Gong, S. Yerci, R. Li, L. Dal Negro and J. Vuckovic, Optics Express, Vol 17, pp (2009)

10 Plasmonic Er-Si light sources Intensity (a.u.) SPP polarization Integrated PL emission enhancement relative to structure without metal grating on top: - 4x in 1D grating - 12x in 2D grating - strongly polarized output in 1D - plasmonic resonance scanned by varying grating period Y. Gong et al, Optics Express 17, pp (2009)

11 Fiber coupled Er-Si light source Er-Si photonic crystal cavity photoluminescence extracted via fiber taper (2.5x improvement relative to free space; 53% taper collection efficiency) G. Shambat et al, submitted to Optics Express (arxiv: )

12 Finite Difference Time Domain (FDTD) Computation Enhancement Cavities were simulated with implementation of FDTD algorithm on GPU/Tesla system Parallel processing of Maxwell s equations on arrays of graphics processing cores More than 10x decrease in computation time Quickly scan parameter space of cavity designs Arrays of GPUs allows further parallelization Potential to be applied to general computation problems GPU GPU Nvidia (donated) Tesla system

13 Inverse Design of Nanophotonic Structures Brute force search to get desired field H (change structure, i.e. ε, a little, simulate structure, get field repeat many times). Takes days, sometimes months! Use complementary optimization, guess optimal cavity field and cavity structure Direct Problem Inverse Problem in in in out out out Using this complementary optimization method in 2D we can quickly (< 10 mins) design resonators with arbitrary field profile J. Lu and J. Vuckovic, Optics Express Vol 18, pp (2010)

14 Other opportunities: Ge-Si light sources in the infrared Stanford University

15 Pseudo-Direct Gap Germanium Heavy n-doping fills the indirect valley Additional carriers can recombine radiatively through direct transition (wavelength = 1550 nm) Tensile strain arises from lattice mismatch during growth on Si Optics Express 17, pp (2009) Collaboration with Yoshio Nishi and Krishna Saraswat, Stanford Proposed by Kimmerling and Michel, Optics Express 15, Issue 18, pp (2007) Also investigated by Kimmerling and Michel, Opt. Lett. 34, (2009) (but in a different structure & no temp. dependence)

16 Germanium Electroluminescence Germanium pn diode fabricated with CMOS compatible process Luminescence observed from direct transition Room temperature 1.6 um electroluminescence from Ge light emitting diode on Si substrate, Szu-Lin Cheng, Jesse Lu, Gary Shambat, Hyun-Yong Yu, Krishna Saraswat, Jelena Vuckovic, Yoshio Nishi, Optics Express, Vol 17, pp (2009) Featured in Stanford News, Laser Focus World, Slashdot

17 Photoluminescence and electroluminescence versus dopant concentration and temperature PL and EL increase with dopant concentration and temperature SL Cheng et al, Optics Express 17, pp (2009)

18 Photonic crystal lasers Stanford University

19 Ultrafast photonic crystal laser Above lasing threshold: τ decay ~ Q τ delay ~ V/Q Need small V and moderate Q τ single ~ 2.13ps τ delay ~1.5ps PhC laser pump 66 GHz 100 GHz For both single cavity and cavity array: f modulation >100 GHz Coupled to quantum wells H. Altug, D. Englund, and J. Vuckovic, Nature Physics 2, pp (2006)

20 Photonic crystal nanocavity array laser Relative to a single cavity laser: P out x100 (>12 µw peak) P threshold x10 ( with β ) f modulation >100GHz Relative to VCSEL: f mod, P thresh, efficiency ~0.2nm H. Altug and J. Vuckovic, Optics Express, vol. 13, pp (2005) IEEE LEOS Newsletter Apr. 2006, Laser Focus World, Phot. Spectra Jan. 2006

21 Photonic crystal electro-optic modulators Stanford University

22 Photonic crystal quantum dots electro-optic modulator D. Englund, B. Ellis, E. Edwards, T. Sarmiento, J. S. Harris, D. A. B. Miller and J. Vuckovic Optics Express, Vol 17, pp (2009), At the moment: InAs/GaAs based, ~1.3µm, room T operation Measured RC~3ns, but could be improved

23 Electro-optic switching with a quantum dot strongly coupled to a nanocavity <fj/operation (0.1aJ possible) ~10GHz speed (currently 150MHz because of RC constant) A. Faraon, A. Majumdar, H. Kim, P. Petroff & J. Vuckovic, PRL vol. 104, (2010) 23

24 Photonic crystal light sources in the visible Stanford University

25 GaP photonic crystal cavities in the visible Sources: LEDs and lasers, especially green Couple to visible emitters previously inaccessible to PCs, including NV centers and (bio)molecules Ultrasmall volume sensors Conversion of light between visible and IR 500 nm Q=10,000 DNQDI PL GaP material: Fariba Hatami, Humboldt University, Berlin Molecules: W.E. Moerner, Stanford University K. Rivoire et al, Appl. Phys. Lett 93, article (2008) 25

26 SHG in GaP photonic crystal cavities Second harmonic L 2, Q= µm slope=2.02 Several orders of magnitude higher efficiency than in prior SHG work in GaAs, InP K. Rivoire et al, Optics Express. Vol 17, pp (2009)

27 1D PC cavities in SiO nm Cavities made in SiO 2 (n=1.46), with CMOS compatible process High theoretical Q (> 15,000), as 1D nano beam cavities have high degree of confinement in transverse directions Experimental Q > 5,000, spanning red portion of visible wavelength range Q > 5,000 Y. Gong and J. Vuckovic, APL 96, (2010) 27

28 Conclusions Si CMOS compatible light sources: Er-Si photonic crystal light emitters at 1540nm Er-Si plasmonic light emitters at 1540nm SiGe electroluminescent LED at 1550nm PC lasers and electro-optic modulators: Integrated PC cavity-waveguide modulator (w/qds) Electroluminescence from PC cavity with lateral junction Single QD-PC cavity modulator with sub-fj control Stanford University PC cavities in the visible: Efficient probing of molecule fluorescence Efficient second harmonic generation Inexpensive, can be made in low index materials

29 Acknowledgements Students Yiyang Bryan Nicolas Maria Kelley Hatice Altug (-> BU) Dirk Englund (->Columbia) Andrei Faraon (->HP) Nicolas Manquest Arka Majumdar Maria Makarova Andrei Jesse Arka Gary Yiyang Gong Jesse Lu Collaborators: Kelley Rivoire Gary Shambat Boston University: Luca Dal Negro, Selcuk Yerci, Rui Li Stanford: Yoshio Nishi, Szu-Lin Cheng, Krishna Saraswat, H-Y Yu, T. Sarmiento, J. S. Harris, D. A.B. Miller UCSB: Hyochul Kim, Pierre Petroff NIST: Sae Woo Nam, Marty Stevens, Burm Baek Humboldt U, Berlin: Fariba Hatami e e