NIRT: Photon and Plasmon Engineering in Active Optical Devices based on Synthesized Nanostructures

1

NIRT Photon and Plasmon Engineering in Active
Optical Devices based on Synthesized
Nanostructures Marko Loncar1, Mikhail Lukin2 and
Hongkun Park3 1Harvard Electrical Engineering,
2Harvard Physics, 3Harvard Chemistry

• Program Goals
• Understanding and engineering of fundamental
  properties of light generation and control in
  active optical nanostructures
• Development of robust and practical devices and
  systems for optical and quantum optical
  communication and information processing (e.g.
  single photon sources, low-power/single-photon
  switches, nano-lasers).
• Answer important questions that pertain to
  hybrid nanostructures integration of different
  fabrication techniques, integration across
  different length-scales, efficient information
  exchange between nano-structures and macro-world,
  light-matter interaction on a nanoscale.

• Approach
• Combination of bottom-up synthesized nanoscale
  light emitters and metallic (Ag, Au) nanowires
  with top-down nanofabricated advanced structures
  for light localization, such as nano-scale
  surface plasmons and photonic crystals.
• Bottom-up synthesized nanocrystal quantum dots
  (QDs) offer number of advantages over
  conventional epitaxially grown QDs, including
  better uniformity, ease of fabrication and
  integration with passive optical platforms, and
  multi-wavelength operation.
• Synthesized metallic nanowires can be
  crystalline, and are superior to top-down
  fabricated metallic waveguides (lower loss)
• Photonic crystal cavities can enhance radiation
  from QDs due to large Purcell factor enabled by
  their large quality factor and small mode volume.

Anti-bunching single photon source Second-order
self-correlation function G(2)(t ) of QD
fluorescence. The number of coincidences at t 0
goes almost to zero, confirming that the QD is a
single-photon source. The width of the dip
depends on the total decay rate Gtotal and the
pumping rate R. Second-order cross-correlation
function between fluorescence of the QD and
scattering from the NW end. This data was taken
by looking at coincidences between photon
emission from the QD (red circle) and NW end
(blue circle). A.Akimov et al, Nature, 450, 402
(2007)
Purcell factor as a function of wire diameter.
?630nm
Schematic of hybrid quantum plasmonic device that
combines bottom-up synthesis and top-down
nanofabrication.

• Normalized energy flux for an emitter
• positioned (from top to bottom) at distances k0d
  0002, 0.2, and 0.7 from the nanowire.
• The first plot is mostly dark and indicates that
  the emitter decays primarily nonradiatively.
• The middle plot demonstrates efficient
  excitation of guided plasmons at the final radius
  R.
• The last plot exhibits the typical lobe pattern
  associated with radiative decay.
• D. E. Chang et al., PRL, 97, 053002 (2006)

Effective mode-index (neff) of Ag nanowires
(?630nm) vs NW radius (r). Insets mode profile
for r50nm and r150nm. In contrast to dielectric
waveguides, Ag NW supports guided mode even when
rltlt ?. This ultra-confined plasmon mode is ideal
for optical wiring of nanoscale quantum
emitters.
Optimized efficiency of single-photon generation
vs R, including coupling to the dielectric
waveguide. Solid line theoretical efficiency
using a nanowire. Dotted line theoretical
efficiency using a nanotip.

• Broader Impact
• Powerful and unique educational opportunities
  for students
• interdisciplinary nature of our NIRT exposes
  students to theoretical work, nanostructure
  synthesis, device physics and engineering,
  nanofabrication and optical characterization.
• team members co-advise students and hold
  bi-weekly joint group meetings
• undergraduate students and minorities
  participate in the efforts of our NIRT through
  the NSF supported Research Experience for
  Undergraduates program.
• The team members give public lectures and
  organize science projects at local public
  schools, mentor high school students and work
  with high school teachers (NSF RET)
• The team members participate in ongoing Harvard
  outreach programs, as well as engage the
  business-oriented public (e.g. Harvard
  Nanotechnology Business Forum, Harvard
  Industrial Outreach Program).
• The knowledge and techniques developed in this
  program will find application in other fields,
  including life sciences (e.g. surface-plasmon
  enhanced sensing techniques), advanced
  photolithography, particle manipulation
  (tweezing), etc.

Future Directions
Schematic diagram of transistor operation
involving a three-level emitter. In the storage
step, a gate pulse consisting of zero or one
photon is split equally in counter-propagating
directions and coherently stored using an
impedance-matched control field (t ). The storage
results in a spin flip conditioned on the photon
number. A subsequent incident signal field is
either transmitted or reflected depending on the
photon number of the gate pulse, owing to the
sensitivity of the propagation to the internal
state of the emitter. D. E. Chang et al., Nature
Physics, 3, 807 (2007)
Hybrid photonic crystal /semiconductor
nanocrystal single photon source, ultra low-power
switch, and quantum/ optoelectronics networks.

1. Schematic of single photon source based on
   nitrogen-vacancy (NV) color center in diamond
2. High-Q (Qgt20,000) optical cavity design for
   diamond nanophotonics.
3. Ultra-compact optical cavity fabricated in
   single-crystal diamond.