Transcript NIRT: Photon and Plasmon Engineering in Active Optical

NIRT: Photon and Plasmon Engineering in Active Optical Devices
Based on Synthesized Nanostructures
1
Lončar ,
Marko
Mikhail
and Hongkun
1Harvard Electrical Engineering, 2Harvard Physics, 3Harvard Chemistry
Program Goals
2
Lukin
3
Park
Approach
Quantum Plasmonics
• 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.
new approach to light-matter interface based on sub-wavelength
localization and guiding of optical radiation on metallic nanowires
• 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.
Hybrid Nanophotonic-Plasmonic Platform for Efficient
Generation and Extraction of Photons
(Tapered) Optical fiber
Coupler
Electrical Detection of Plasmons
The detection of plasmons is achieved by generation of electron-hole pairs within a semiconductor (Ge
or InAs) nanowires followed by charge separation induced by a local electric field.
SiNx waveguide
Ag nanowire
Ag nanowire
plasmon waveguide
SiO2 bottom cladding
Quantum
dot
Coupling of CdSe quantum dots to surface plasmons supported on Ag NW. The red circle
corresponds to the position of the QD coupled to nanowire. Ch III: excitation laser was
focused on the circled QD. The largest bright spot corresponds to the QD fluorescence,
while two smaller spots correspond to SPs scattered from the NW ends. Blue circle indicate
farthest end of the wire, used for photon cross-correlation measurements.
A.Akimov et al., Nature, 450, 402 (2007)
SiNx waveguide
Emission from QDs coupled to nanowire,
collected through an optical fiber
Anti-bunching & single photon emission
Second-order self-correlation function G(2)(τ ) of
QD fluorescence. The number of coincidences at τ
= 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 Γtotal and the pumping rate R.
Aligned Ag nanowire
Waveguide couplers
SiNx waveguide
Tapered fiber
Contacts
Ge nanowire
(detector)
Composite image: SEM micrograph and detected current
when laser beam is scanned across the structure. Red
spots on Ag nanowire ends correspond to 20pA current
signal when laser is focused on Ag nanowire ends.
Falk, Koppens et al. (2008)
Reflection
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).
• Zero-bias efficiency :1~10% (i.e. 0.01 ~ 0.1
•
electrons/plasmon)
Bias: efficiency ~10 electrons/plasmon. The intrinsic
gain mechanism is due to transiently trapped charges
modulating the conductivity of the Ge nanowire.
Fluorescence
Ag NW
Ge NW
Photocurrent
Ag nanowire ends
Single-plasmon detector: The Ge-nanowire can detect a signal from CdSe
quantum dots coupled to the Ag nanowire.
Future Directions
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.
Single-photon transistor.
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)
Strong-coupling in SiNx nanocavities embedded
with diamond nanocrystals: We designed a photonic
Ultra-high Q cavities based on semiconductor
nanowires: By defining one-dimensional
crystal nanocavity with a quality factor Q>106, a mode
volume of Vmod=0.78(λ/n)3, and an operating wavelength
of λ=637 nm in SiNx (n=2). Strong coupling between a
nanocrystal with an embedded nitrogen-vacancy colorcenter and the cavity mode is achievable for a range of
cavity dimensions.
M. W. McCutcheon & M. Loncar, Optics Express (in press)
photonic crystal at nanowire ends cavities with Q~106 and
Vmode <0.2(λ/n)3 have been designed. Our cavities are wellsuited for the realization of nanowire-based low-threshold
lasers, single-photon sources and quantum optical devices that
operate in the strong-coupling limit.
Y. Zhang & M. Loncar, Optics Express, 16, 17401 (2008)