816 research outputs found
Pliable Polaritons: Wannier Exciton Plasmon Coupling in Metal Semiconductor Structures
Plasmonic structures are known to support the modes with subwavelength
volumes in which the field matter interactions are greatly enhanced. Coupling
between the molecular excitations and plasmons leading to formation of
plexcitons has been investigated for a number of organic molecules. However,
plasmon-exciton coupling in metal semiconductor structures have not experienced
the same degree of attention. In this work we show that the very strong
coupling regime in which the Rabi energy exceeds the exciton binding energy is
attainable in semiconductor cladded plasmonic nanoparticles and leads to
formation of Wannier Exciton Plasmon Polariton (WEPP) that is bound to the
metal nanoparticle and characterized by dramatically smaller (by factor of few)
excitonic radius and correspondingly higher ionization energy. This higher
ionization energy exceeding approaching 100meV for the CdS/Ag structures may
make room temperature Bose Einstein condensation and polariton lasing in
plasmonic/semiconductor structures possibl
Fast and slow light in zig-zag microring resonator chains
We analyze fast and slow light transmission in a zig-zag microring resonator
chain. This novel device permits the operation in both regimes. In the
superluminal case, a new ubiquitous light transmission effect is found whereby
the input optical pulse is reproduced in an almost simultaneous manner at the
various system outputs. When the input carrier is tuned to a different
frequency, the system permits to slow down the propagating optical signal.
Between these two extreme cases, the relative delay can be tuned within a broad
range
Optimal design and quantum limit for second harmonic generation in semiconductor heterostructures
The optimal design for infrared second harmonic generation (SHG) is
determined for a GaAs-based quantum device using a recently developed genetic
approach. Both compositional parameters and electric field are simultaneously
optimized, and the quantum limit for SHG, set by the trade-off between large
dipole moments (favouring electron delocalization) and large overlaps
(favouring electron localization), is determined. Optimal devices are generally
obtained with an asymmetric double quantum well shape with narrow barriers and
a graded region sideways to the largest well. An electric field is not found to
lead to improved SHG if compositional parameters are optimized.Comment: 5 pages, 2 figures embedded. To apper in J. App. Phys. (Jan 2nd,
2001
Photonic Time Crystals and Parametric Amplification: similarity and distinction
Photonic Time crystals (PTC) arise in time-modulated media when the frequency
of modulation of permittivity is on the order of twice the frequency of light
and are manifested by the generation and amplification of so-called time
reversed waves propagating in the direction opposite to the incoming light.
Superficially, the observed phenomenon bears resemblance to the widely known
phenomena of optical parametric generation (OPG) and amplification (OPA) using
second or third order optical nonlinearities. I show that while indeed the same
physical mechanism underpins both PTC and OPA , the difference arises from the
boundary conditions. Thus , while dispersion for both PTC and OPA exhibit the
same bandgap in momentum space, only in the case of PTC can one have
propagation in that bandgap with exponential amplification. I also show that
PTC can be engineered with both second and third order nonlinearities, and that
rather unexpectedly, modulating permittivity on the ultrafast (few fs) rate is
not a necessity, and that one can emulate all the PTC features using materials
with a few picoseconds response time commensurate with the propagation time
through the medium
- …