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Stanford University
Nanophotonic Devices for Classical and Quantum Information Processing
Nano-tech/Bio workshop, Stanford, CA, Feb. 2010
Yiyang Gong, Dirk Englund, Bryan Ellis, Andrei Faraon, Jesse Lu Maria Makarova, Arka Majumdar, Kelley Rivoire, Gary Shambat,
and Jelena Vučković
J. Vuckovic, Stanford University
(devices for quantum info. processing, single QD modulators & switches)
quantum photonics
Nanoscale and quantum photonics group research Nanophotonic structures:
Nanoscale localization and manipulation of light
Quantum dots (QDs), Q-wells,nanocrystals:
4xMQW InGaAsP
Light emitters
0.2nm
(High speed, low threshold lasers, optical switches, modulators - Silicon CMOS compatible)
Optical communications and interconnects
classical info. processing High-density nanophotonic and quantum circuits
200nm
+
J. Vuckovic, Stanford University 3
Photonic crystals/Plasmonic gratings Photonic crystal cavity • 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)
Plasmonic structure • Confinement by
– Collective charge oscillation at metal-dielectric interface
• Confinement into V<<(λ/n)3, breaks diffraction limit
• moderate quality factors Q (ohmic losses)
J. Vuckovic, Stanford University
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
Stanford University
Enhancement of Er-doped amorphous Silicon nitride by photonic crystal
and plasmonic structures
J. Vuckovic, Stanford University
Er-doped silicon photonic crystal cavities Theory: Q=32,000, V=0.85(λ/n)3
Experiment: Q>15,000
M. Makarova*, Y. Gong*, et. al. IEEE J. Sel. Top. Quant. Electronics Vol 16, pp. 132-140 (2010)
Hybrid membrane: 110 nm Er:SiNx
250nm Si
a = 410nm
Er doped Silicon rich nitride
L. Dal Negro et al, IJSTQE 12, 6, 1628 (2006)
PL@10K PL@300K
J. Vuckovic, Stanford University
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)
J. Vuckovic, Stanford University
Purcell effect in Er-doped silicon photonic crystal cavities
• Purcell factor at room T: 2.4 • Purcell factor at low T: 11-17
Y. Gong, M. Makarova et al, Optics Express 18, 2601 (2010)
J. Vuckovic, Stanford University
Plasmonic Er-Si light sources • 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 Er-doped amorphous silicon rich nitride in MIM
2 µm Y. Gong, S. Yerci, R. Li, L. Dal Negro and J. Vuckovic, Optics Express, Vol 17, pp 18651-18658 (2009)
B
|E|2
Co-sputterting
Er:SiNx
J. Vuckovic, Stanford University
Plasmonic Er-Si light sources
Y. Gong et al, Optics Express 17, pp 18651-18658 (2009)
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
Inte
nsity
(a.u
.)
SPP polarization
J. Vuckovic, Stanford University
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:1001.0430)
J. Vuckovic, Stanford University
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
J. Vuckovic, Stanford University
• 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
• Using this complementary optimization method in 2D we can quickly (< 10 mins) design resonators with arbitrary field profile
Inverse Design of Nanophotonic Structures
in in
out out
in
out
Direct Problem Inverse Problem
J. Lu and J. Vuckovic, Optics Express Vol 18, pp. 3793-3804 (2010)
Stanford University
Other opportunities: Ge-Si light sources in the infrared
J. Vuckovic, Stanford University
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. 10019-10024 (2009)
Collaboration with Yoshio Nishi and Krishna Saraswat, Stanford
• Proposed by Kimmerling and Michel, Optics Express 15, Issue 18, pp. 11272-11277 (2007) • Also investigated by Kimmerling and Michel, Opt. Lett. 34, 1198-1200 (2009) (but in a different structure & no temp. dependence)
J. Vuckovic, Stanford University
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 10019-10024 (2009) Featured in Stanford News, Laser Focus World, Slashdot
J. Vuckovic, Stanford University
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 10019 10024 (2009)
Stanford University
Photonic crystal lasers
J. Vuckovic, Stanford University
Ultrafast photonic crystal laser
τsingle ~ 2.13ps
Above lasing threshold: τdecay ~ Q τdelay ~ V/Q
H. Altug, D. Englund, and J. Vuckovic, Nature Physics 2, pp. 484-488 (2006)
Need small V and moderate Q
100 GHz
66 GHz
fmodulation>100 GHz
For both single cavity and cavity array:
pump
PhC laser
τdelay ~1.5ps
Coupled to quantum wells
J. Vuckovic, Stanford University
~0.2nm
Photonic crystal nanocavity array laser Relative to a single cavity laser: • Pout x100 (>12 µW peak) • Pthreshold x10 (↓ with β ↑) • fmodulation >100GHz Relative to VCSEL: • fmod↑, Pthresh↓, efficiency↑
• H. Altug and J. Vuckovic, Optics Express, vol. 13, pp. 8819-8828 (2005) • IEEE LEOS Newsletter Apr. 2006, Laser Focus World, Phot. Spectra Jan. 2006
Stanford University
Photonic crystal electro-optic modulators
J. Vuckovic, Stanford University
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 15409-15419 (2009),
At the moment: • InAs/GaAs based, • ~1.3µm, room T operation • Measured RC~3ns, but could be improved
J. Vuckovic, Stanford University
Electro-optic switching with a quantum dot strongly coupled to a nanocavity
23
A. Faraon, A. Majumdar, H. Kim, P. Petroff & J. Vuckovic, PRL vol. 104, 047402 (2010)
• <fJ/operation (0.1aJ possible) • ~10GHz speed (currently 150MHz because of RC constant)
Stanford University
Photonic crystal light sources in the visible
J. Vuckovic, Stanford University
GaP photonic crystal cavities in the visible
25
• 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
GaP material: Fariba Hatami, Humboldt University, Berlin Molecules: W.E. Moerner, Stanford University
K. Rivoire et al, Appl. Phys. Lett 93, article 063103 (2008)
Q=10,000
DNQDI PL
500 nm
J. Vuckovic, Stanford University
SHG in GaP photonic crystal cavities
Second harmonic
L2, Q=6000
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 22609-22615 (2009)
1 µm
J. Vuckovic, Stanford University
1D PC cavities in SiO2
27
Q > 5,000
Y. Gong and J. Vuckovic, APL 96, 031107 (2010)
• Cavities made in SiO2 (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
400 nm
Stanford University
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
PC cavities in the visible: • Efficient probing of molecule fluorescence • Efficient second harmonic generation • Inexpensive, can be made in low index materials
J. Vuckovic, Stanford University http://www.stanford.edu/group/nqp
Students
Collaborators: 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
Acknowledgements
Jesse
Gary
Maria Yiyang
e¯
e¯
Bryan Kelley
Andrei
Arka
Nicolas
Hatice Altug (-> BU) Nicolas Manquest
Dirk Englund (->Columbia) Arka Majumdar
Andrei Faraon (->HP) Maria Makarova
Yiyang Gong Kelley Rivoire
Jesse Lu Gary Shambat