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